Computer programing and solving

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Chapter 6 Arrays and ArrayLists
Java Arrays:
1. Definition: An array in Java is a fixed-size, ordered collection of elements of the same data type.
It is a contiguous block of memory that can store multiple values of the same type.
2. Declaration: Arrays are declared using square brackets ([]) after the data type. For example, int[]
numbers; declares an integer array.
3. Initialization: Arrays can be initialized using the new keyword, like numbers = new int[5];, which
creates an integer array with space for five elements.
4. Accessing Elements: Array elements are accessed using square brackets and zero-based indices.
For example, to access the first element: int firstElement = numbers[0];
5. Length: The length of an array is fixed and can be obtained using the length property, e.g., int
arrayLength = numbers.length;
6. Iterating Through Arrays: Arrays can be traversed using loops like for or foreach to access and
manipulate each element.
7. Arrays of Objects: Arrays can hold objects of any class, allowing you to create arrays of custom
objects.
8. Arrays of Primitives: Arrays can also hold primitive data types like int, char, boolean, etc.
ArrayLists (java.util.ArrayList):
1. Definition: ArrayList is a part of the Java Collections Framework and is a dynamic array-like data
structure that can resize itself automatically. It allows you to store and manipulate a collection of
objects.
2. Import Statement: To use ArrayList, you need to import it: import java.util.ArrayList;
3. Declaration and Initialization: An ArrayList can be declared and initialized like this:
Code example
ArrayList numberList = new ArrayList();
1. Adding Elements: You can add elements to an ArrayList using the add() method, e.g.,
numberList.add(42);
2. Accessing Elements: Elements in an ArrayList are accessed using the get() method, e.g., int value
= numberList.get(0);
3. Size: Unlike arrays, ArrayLists can dynamically change in size. You can get the current size using
the size() method.
4. Removing Elements: Elements can be removed using methods like remove(int index) or
remove(Object obj).
5. Iterating Through ArrayLists: You can use an enhanced for loop or an Iterator to traverse
through the ArrayList.
6. Generics: ArrayLists are generic, which means you can specify the type of objects they will hold.
This helps ensure type safety.
7. Auto-Resizing: ArrayLists automatically resize themselves when they reach their capacity,
making them more flexible than arrays.
8. Performance: ArrayLists are generally slower for random access than arrays but more efficient
for dynamic resizing and inserting/removing elements.
9. Search and Manipulation: ArrayLists provide methods for searching (contains(), indexOf()) and
manipulation (add(), remove(), set()).
In summary, Java arrays provide a fixed-size, low-level way to store elements of the same type, while
ArrayLists offer dynamic resizing and additional features for working with collections of objects. The
choice between the two depends on the specific requirements of your program.
Copying Array
To copy arrays in Java, you have several options, depending on your requirements. Here are a few
common methods:
Using a Loop: You can manually copy the elements from one array to another using a loop. Here’s an
example for copying an integer array:
Code example
int[] sourceArray = {1, 2, 3, 4, 5};
int[] destinationArray = new int[sourceArray.length];
for (int i = 0; i < sourceArray.length; i++) { destinationArray[i] = sourceArray[i]; } Using System.arraycopy(): Java provides a built-in method System.arraycopy() for efficiently copying elements between arrays. Here's how you can use it: Code example int[] sourceArray = {1, 2, 3, 4, 5}; int[] destinationArray = new int[sourceArray.length]; System.arraycopy(sourceArray, 0, destinationArray, 0, sourceArray.length); The method signature is: System.arraycopy(Object src, int srcPos, Object dest, int destPos, int length) System.arraycopy(Object src, int srcPos, Object dest, int destPos, int length) int[] sourceArray = {1, 2, 3, 4, 5}; int[] destinationArray = Arrays.copyOf(sourceArray, sourceArray.length); Using Arrays.copyOfRange(): If you want to copy a specific range of elements from an array, you can use Arrays.copyOfRange(). These methods allow you to copy the contents of one array to another, whether it's a complete copy or a subset of the source array. Choose the method that best fits your specific copying requirements. Passing Arrays to Methods In Java, you can pass arrays to methods just like you pass any other variable. When you pass an array to a method, you are essentially passing a reference to the array, not a copy of the array itself. This means that any changes made to the array inside the method will affect the original array outside the method. Here's how you can pass arrays to methods: public class ArrayExample { public static void main(String[] args) { int[] numbers = {1, 2, 3, 4, 5}; // Calling a method and passing the array modifyArray(numbers); // The original array has been modified for (int num : numbers) { System.out.print(num + " "); } } public static void modifyArray(int[] arr) { // Modify the array within the method for (int i = 0; i < arr.length; i++) { arr[i] *= 2; } } } In the example above, we define a method modifyArray that takes an integer array as a parameter. Inside the method, we double the values of each element in the array. When we call this method with the numbers array, the original array is modified, and those modifications are reflected outside the method. Keep in mind the following points when passing arrays to methods: 1. Changes made to the elements of the array inside the method will affect the original array since you're working with a reference to the same array. 2. If you want to prevent a method from modifying the original array, you can create a copy of the array within the method and work with the copy. 3. You can return arrays from methods in Java just like any other data type, allowing you to encapsulate array creation and manipulation within methods. Here's an example of returning an array from a method: public class ArrayExample { public static void main(String[] args) { int[] numbers = createArray(5); for (int num : numbers) { System.out.print(num + " "); } } public static int[] createArray(int size) { int[] newArray = new int[size]; for (int i = 0; i < size; i++) { newArray[i] = i + 1; } return newArray; } } In this example, the createArray method creates and initializes an array of a specified size and returns it to the calling code. Two-dimensional Arrays A two-dimensional array in Java is an array of arrays, where each element of the array is itself an array. It can be thought of as a table or grid of elements, where rows and columns define the dimensions of the array. Two-dimensional arrays are often used to represent matrices, tables, or grids of data. Here's how to declare, initialize, and work with two-dimensional arrays in Java: Declaration and Initialization: You can declare a two-dimensional array using square brackets for both dimensions. For example, to declare a 3x4 integer array: int[][] twoDArray = new int[3][4]; This creates a 3x4 array filled with default values (0 for integers). You can also initialize a two-dimensional array with specific values: int[][] twoDArray = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } }; Accessing Elements: Elements in a two-dimensional array are accessed using two indices: the row index and the column index. Both indices start from 0. For example, to access the element in the second row and third column: int element = twoDArray[1][2]; // Row 2 (index 1), Column 3 (index 2) Iterating Through a 2D Array: You can use nested loops to iterate through all the elements of a two-dimensional array. Here's an example that prints all elements of the array: for (int i = 0; i < twoDArray.length; i++) { for (int j = 0; j < twoDArray[i].length; j++) { System.out.print(twoDArray[i][j] + " "); } System.out.println(); // Move to the next row } Multidimensional Arrays: Java allows you to create arrays of more than two dimensions, often referred to as multidimensional arrays. For example, a three-dimensional array can be declared and initialized like this: int[][][] threeDArray = new int[3][4][5]; In practice, you can have as many dimensions as needed, but readability and understanding become more challenging as the number of dimensions increases. Two-dimensional arrays are versatile and are commonly used in various programming tasks, such as representing game boards, spreadsheet-like data structures, and storing matrices for mathematical operations. Array Algorithms Here are some common array algorithms that you might encounter in programming: 1. Linear Search: Search for a specific element in an array by sequentially checking each element until a match is found or the end of the array is reached. Linear search has a time complexity of O(n) for an array of n elements. 2. Binary Search: Search for a specific element in a sorted array by repeatedly dividing the search interval in half. Binary search has a time complexity of O(log n) for a sorted array. 3. Sorting Algorithms: • Bubble Sort: Repeatedly swap adjacent elements if they are in the wrong order until the entire array is sorted. Bubble sort has a time complexity of O(n^2). • Selection Sort: Find the minimum element from the unsorted portion and move it to the beginning of the sorted portion of the array. Selection sort also has a time complexity of O(n^2). • Insertion Sort: Build a sorted array by repeatedly taking elements from the unsorted portion and inserting them into their correct position in the sorted portion. It has a time complexity of O(n^2). • Merge Sort: Divide the array into smaller sub-arrays, sort them, and then merge them back together in a sorted manner. Merge sort has a time complexity of O(n log n). • Quick Sort: Choose a "pivot" element and partition the array into two sub-arrays: one with elements less than the pivot and another with elements greater than the pivot. Recursively sort the sub-arrays. Quick sort also has an average time complexity of O(n log n). 4. Maximum and Minimum Element: Find the maximum and minimum elements in an array by iterating through the array and keeping track of the current maximum and minimum values. 5. Reverse Array: Reverse the elements of an array, effectively flipping the order of the elements. 6. Duplicates Detection: Detect duplicate elements in an array by using a data structure like a HashSet or by sorting the array and checking adjacent elements. 7. Counting Occurrences: Count the number of occurrences of a specific element in an array by iterating through the array and keeping a count. 8. Finding Missing Element: Find a missing element in an array of consecutive integers. This can be done efficiently using mathematical formulas. 9. Rotate Array: Rotate the elements of an array by a specified number of positions, either left or right. 10.Kth Largest/Smallest Element: Find the Kth largest or Kth smallest element in an array using techniques like quickselect or a priority queue. 11.Subarray Sum: Find a subarray (contiguous sequence of elements) with a specific sum, often using techniques like the sliding window or prefix sum. 12.Intersection and Union of Arrays: Compute the intersection and union of two arrays, which can be useful for various set operations. These algorithms provide a foundation for working with arrays in various programming tasks and are essential to solving a wide range of problems efficiently. Depending on the specific problem, you may need to choose the most suitable algorithm to achieve the desired outcome while considering factors like time complexity and space complexity. The ArrayList ArrayList is a dynamic data structure provided by the Java Collections Framework that is built on top of arrays. It offers many useful features and methods for working with lists of objects. Here are some additional details and operations you can perform with ArrayLists: 1. Dynamic Sizing: ArrayLists can automatically resize themselves when elements are added or removed, making them convenient for situations where the number of elements is not known in advance. 2. Capacity: An ArrayList has a capacity, which is the maximum number of elements it can hold without resizing. When the capacity is exceeded, the ArrayList automatically grows by creating a larger underlying array and copying the elements. 3. Initialization with Capacity: You can specify an initial capacity when creating an ArrayList to optimize performance if you know the approximate size of the list in advance. For example: ArrayList list = new ArrayList(10); // Initial capacity of 10 1. Adding Elements: • add(E element): Adds an element to the end of the ArrayList. • add(int index, E element): Inserts an element at the specified index, shifting existing elements to the right. 2. Removing Elements: • remove(int index): Removes the element at the specified index. • remove(Object obj): Removes the first occurrence of the specified object. • clear(): Removes all elements from the ArrayList. 3. Checking for Elements: • contains(Object obj): Checks if the ArrayList contains a specific object. • isEmpty(): Checks if the ArrayList is empty. 4. Accessing Elements: • get(int index): Retrieves the element at the specified index. • set(int index, E element): Replaces the element at the specified index with a new element. 5. Size and Capacity: • size(): Returns the current number of elements in the ArrayList. • ensureCapacity(int minCapacity): Increases the capacity of the ArrayList to at least the specified minimum capacity. 6. Iterating Through ArrayList: • You can use for-each loops, iterators, or streams to iterate through the elements of an ArrayList. 7. Conversion: • You can convert an ArrayList to an array using toArray(), and vice versa, using Arrays.asList(). 8. Sorting: • You can sort an ArrayList using the Collections.sort() method if the elements are comparable. 9. Sublist: • You can create a sublist of an ArrayList using the subList(int fromIndex, int toIndex) method. 10.ArrayList vs. LinkedList: • ArrayList is backed by an array and is efficient for random access but less efficient for frequent insertions and removals in the middle. LinkedList, on the other hand, is more efficient for frequent insertions and removals but less efficient for random access. 11.Synchronization: • ArrayList is not synchronized, which means it is not thread-safe. If you need thread safety, you can use Collections.synchronizedList() to create a synchronized ArrayList. 12.Performance Considerations: • The time complexity of various operations on an ArrayList, such as adding and accessing elements, is important to consider when choosing it for a specific use case. ArrayLists are widely used in Java for managing collections of objects due to their flexibility, ease of use, and dynamic sizing capabilities. They are suitable for many list-based data storage and manipulation tasks in Java programs. Regenerate Introduction to Java Computer Programming and Problem Solving Second Edition Chris Simber Assistant Professor, Computer Science Rowan College at Burlington County Cataloging Data Names: Simber, Chris, author. Title: Introduction to Java: Computer Programming and Problem Solving Subjects: Java (Computer Programming Language) Chris Simber Assistant Professor of Computer Science Rowan College at Burlington County Author contact: csimber@RCBC.edu Introduction to Java: Computer Programming and Problem Solving by Christopher Simber is licensed under a Creative Commons Attribution – NonCommercial-ShareAlike 4.0 International License, except where otherwise noted. Images may not be distributed individually. All screenshots included on the basis of Fair Use. Creative Commons — Attribution-NonCommercial-ShareAlike 4.0 International — CC BYNC-SA 4.0 Under the following terms: Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. creativecommons.org Introduction This book is intended for use in an introductory course in programming using the Java programming language, and includes content for students who are not familiar with programming. The book introduces general computer information and basic computer operations, as well as software engineering principles and processes used in industry to implement computer-based solutions. Algorithm development and problem-solving techniques are introduced as well. The Eclipse integrated development environment (IDE) is utilized and instructions to obtain, install, and “Getting Started in Eclipse” are provided in the appendices. The goal is to provide students with an overview of computers, software engineering tools and techniques, and to introduce them to computer programming in Java quickly for hands-on instruction. The examples and exercises reinforce the material being introduced while building on previous material covered, and follow the programming standards for Java publicized by the World Wide Web Consortium (W3C) and set forth in the Java Coding Guidelines created by Joe McManus MGR at Carnegie Mellon University, Software Engineering Institute. Appendix G provides an adequate abridgement of programming standards. The in-chapter exercises are numbered for clarity using a shaded box, and can be used as in-class exercises or as assignments. The Java version in use at the time of this writing is Version 8. The Integrated Development Environment (IDE) selected is Eclipse which is free to download and use. The Eclipse interface has the common look and feel associated with most integrated development environments and is used extensively in industry. Instructions for obtaining and installing Eclipse are provided in Appendix B, including resolving the most common JRE and JDK issues. Getting started in Eclipse is provided in Appendix C with a sample start-up program. Links to the Eclipse web site, Java Tutorials, and the Java Coding Guidelines are included in Appendix F which also includes a link to the Java Tutorial at the W3Schools website. There are end-of-chapter assignments, and an answer key, exams, and accompanying lecture slides are available. Acknowledgements: Rowan College at Burlington County Student Feedback Revision History: First Edition: August 2022 Second Edition: January 2023 Changes to the Second Edition include minor rewording, corrections to typographical errors, and an additional assignment (#2B) in chapter 2. Contents Chapter 1 Computers and Programming 1 Chapter 2 Java Language Basics 19 Chapter 3 Decision Structures and Boolean Logic 53 Chapter 4 Loops and Repetition Structures 81 Chapter 5 Methods, Modules, and Basic Graphics 111 Chapter 6 Arrays and ArrayLists 139 Chapter 7 File Operations and Exceptions 167 Chapter 8 Classes and Objects 191 Chapter 9 Inheritance and Interfaces 227 Chapter 10 Graphical User Interfaces 253 Chapter 11 GUI Programs 289 Chapter 12 Technology and Society 318 Appendix A ASCII Character Set (partial list) Appendix B Obtaining and Installing Eclipse Appendix C Getting Started with Eclipse Appendix D Modular Programming Appendix E Creating and Input Data File Appendix F Helpful Links to Information Appendix G Java Programming Style and Standards Appendix H Multiple Panels and Layout Managers Example “Five minutes of design time, will save hours of programming” – Chris Simber 1 Chapter 1 Computers and Programming Computers are simply data processing devices. They are machines that receive input, process it in some way, and produce output. Computer programs are made up of a series of statements that tell a computer what to do and in what order to do it. These programs provide a sequence of small steps for the computer to execute and produce the desired result. Millions or even billions of these small steps are being executed by the computer as we run programs. This may seem odd to the casual computer user, but these small steps combine to provide what appear to be seamless operations as we interact with the computer. Computer programs are referred to as software and they are needed to make the computer useful. People who design, write, and test software are commonly referred to as software engineers, software developers, or computer programmers. To better understand the computing process and programming in general, a familiarity with the parts that make up a computer is necessary. The Central Processing Unit (CPU) Any part of the computer that we can physically touch (including inside the casing) is referred to as hardware. One important piece of hardware is the Central Processing Unit CPU which is the “Brains” of the computer. The CPU performs millions of basic instructions per second and controls computer operations. The CPU has two parts. The Arithmetic Logic Unit (ALU) handles Chapter 1 Computers and Programming 2 basic arithmetic and comparisons of data such as less than, greater than, equivalent, and not equivalent. The Control Unit retrieves and decodes program instructions and coordinates activities within the computer. Brown and Green Computer Processor Pixabay is licensed under CC0 Figure 1.1 - Central Processing Unit (CPU) The CPU (shown upside down above) has pins that plug into a socket located on a circuit board called the motherboard. Main Memory RAM stands for Random Access Memory and is often referred to as main memory. RAM is a series of memory chips on a circuit board installed in the computer on the motherboard along with the CPU. The memory in these chips contains a series of memory addresses that enable the computer to store and locate information. These memory addresses are volatile and when the computer is turned off, RAM does not retain information. It is erased. When a program is launched, the program is copied into RAM for the CPU to use. RAM by Headup222 is licensed under Pixabay License Figure 1.2 - Laptop Main Memory (RAM) The CPU can access instructions and data from RAM very quickly, and RAM is located close to the CPU on the motherboard. The RAM circuit card for a laptop Chapter 1 Computers and Programming 3 computer is shown above. The large rectangles are the memory chips, the notches are an aid for inserting the RAM into position on the motherboard, and the gold edge makes the connections for data access. Since RAM is erased when the computer is turned off, secondary storage is used to retain information. Read Only Memory or ROM contains the startup instructions for the computer including the BIOS or Basic Input Output System. It is non-volatile and retains information between sessions. Secondary Storage Secondary storage devices are non-volatile and the information stored is not erased when the power is off. Secondary storage devices include the hard drive inside the computer, external drives connected to the computer, and flash drives. The hard drive inside the computer may be a disk drive which houses a rotating disk and data access arm (shown below), or a solid-state drive which has no moving parts and operates faster than a traditional disk drive. Laptop-hard-drive-exposed by Evan Amos is licensed under CC BY-SA 3.0 Figure 1.3 - Hard Drive (cover removed) External drives are typically solid-state and connect to the computer through a cable plugged into a USB (Universal Serial Bus) connector, or plug directly into the USB port of the computer as in the case of flash drives. Flash drives use flash memory, and do not have a disk drive. Chapter 1 Computers and Programming 4 Input and Output Devices Input devices are anything that provides input or data for a computer. Common input devices are the keyboard, mouse, microphone, and camera. Output devices include anything that accepts computer output such as monitors, speakers, and printers. Since data files located on storage devices can be used for reading data into a computer or writing output from a computer, they could be considered both input and output devices. Software Computers are machines that follow an input, processing, output sequence of operations and need to be told what to do and in what order to do it. This is accomplished through sets of instructions called software. There are essentially two types of software: system software (Operating Systems), and application programs (all other software). The operating system (OS) provides an interface for us to use computers more easily. Initially command line interfaces were used, followed by menu driven interfaces, and then the Graphical User Interface (GUI) was introduced and has been used since. Most operating systems provide a Graphical User Interface that is now commonly used to interact with the computer. It acts like an orchestra conductor by controlling computer hardware, managing devices connected to the computer, and interacting with programs that are running. Operating systems commonly in use today are Windows, macOS, and Linux. Application software includes the computer programs that we commonly use to accomplish work such as word processors, spreadsheet programs, collaboration tools, and audio/video editing tools, as well as gaming software. The Language of Computers The language of computers is a binary language consisting of ones and zeros. This is the beauty and simplicity of the computer. At the basic level, everything is a 1 or a 0, is either On or Off, Yes or No, True or False. The bit, or binary digit Chapter 1 Computers and Programming 5 used in computing represents a logical state that can be 0 or 1. It is the smallest information representation in a computer. A Byte is 8 bits consisting of a combination of 0s and 1s, and in computers, each letter, number, and special character consists of a binary representation. For example, a lower case “f” is represented in binary as 01100110 in accordance with the ASCII standard (pronounced askee). ASCII stands for the American Standard Code for Information Interchange which was developed as a character encoding standard. The ASCII table consists of 256 binary representations for the 26 uppercase and 26 lowercase letters, and the 9 digits, as well as special characters, punctuation marks, and other symbols and keyboard keys. Appendix A provides a partial list of the binary and decimal representations for the upper and lowercase letters, digits, and punctuation. A portion is shown here with the decimal equivalent. ASCII Table (excerpt) The Unicode standard incorporates the 256 item ASCII standard and expands to include the binary representations for symbols and characters for most of the world’s languages. Unicode 13.0 contains representations for 143,859 characters. Instructions for the computer must be in its’ language including numbers that are stored or used in computations. Numeric integers (whole numbers) are represented in computers using the positions of the bits and powers of 2 starting from right and working left. Binary Number Bit Representations Chapter 1 Computers and Programming 6 As an example, the number 90 would be represented in binary as 01011010. Each bit is either 0 or 1 and is multiplied by the power of 2 at its position. The results are then added together. 0 0 x 27 1 0 1 + 1 x 26 + 0 x 25 + 1 0 1 0 1 x 24 + 1 x 23 + 0 x 22 + 1 x 21 + 0 X 20 (0 x 128) + (1 x 64) + (0 x 32) + (1 x 16) + (1 x 8) + (0 x 4) + (0 x 2) + (0 x 1) 0 + 64 + 0 + 16 + 8 + 0 + 2 + 0 = 90 Binary Number Conversion The limit to the numbers that can be stored using 8 bits is 255 with all 8 bits being 1’s. To store larger numbers, two Bytes would be used with a combination of sixteen 1’s and 0’s. That would allow storing numbers as large as 65535. To store larger numbers, more Bytes could be used. To store negative numbers and floating-point numbers (numbers with a decimal or fractional part), other numbering schemes are used such as the two’s complement and floating-point notation. Images (which are made up of pixels) are stored by converting each pixel to a numeric value which is then stored in binary. Sound is stored using samples that are converted to the nearest numeric value. Programming Languages Although the computers’ language, referred to as machine language, is a binary language, it would be tedious for us to write instructions for computers in Binary. Machine language is one of the two languages commonly referred to as low-level languages for computers, the other being Assembly language. Assembly language consists of very basic instructions like move a value into memory, add another value to that one, and store the result in memory. An assembler is used to convert Assembly language programs into executable machine code. Both of these low-level languages mirror the operations of the CPU in simplicity and basic operations. Chapter 1 Computers and Programming 7 The CPU goes through what is called a machine cycle in which it performs the same series of simple steps: fetch, decode, execute, and store. The instructions executed during a machine cycle are very simple, but billions of instructions can be processed per second. CPU Machine Cycle 1. fetch the required piece of data or instruction from memory 2. decode the instruction 3. execute the instruction 4. store the result of the instruction CPU Machine Cycle The processing power of a CPU is dependent upon the number of instructions that the CPU can execute per second, and is measured in hertz (cycles-persecond). This is often referred to as the CPU clock-speed. This does not refer to a wall clock, but the computer’s clock or the internal timing of the computer. A one-gigahertz (1 GHz) CPU can execute one billion cycles (instructions) per second, and the clock-speed would be one-gigahertz. Writing software (programming) in a low-level language is possible, but high- level languages provide a much easier way. As more software was written, high-level languages were introduced to make programming easier and more efficient. In high-level languages, multiple instructions are combined into a single statement. There are hundreds of high-level languages (700+) that have been developed. Today there are approximately 250 high-level programming languages in use by programmers. Some of these are used extensively, others not so much. Each language was created for a purpose and has benefits and limitations as well as a following, proponents, and detractors. The following is a short list of some popular high-level languages and their intended uses. Chapter 1 Computers and Programming 8 BASIC Beginners All-purpose Symbolic Instruction Code C, C++ powerful general-purpose programming COBOL Common Business-Oriented Language - business programs FORTRAN FORmula TRANslator for math and science Pascal teaching programming Java applications running over the internet JavaScript Web site operations (not related to Java) PHP web server applications and dynamic web pages Python general-purpose applications and data handling Popular High-level Programming Languages Writing software in any of these languages is much easier than the low-level languages of Machine and Assembly, but the computer is still only interested in machine language. To translate programs written in a high-level language to the machine language for the computer, compilers and interpreters are used. A compiler translates the high-level language into a separate machine language program. Software engineers refer to this as compiling or “building” the program. A “Build” is a compiled version of the software and the program can then be run whenever needed because it is a stand-alone executable program. Java uses a compiler. An interpreter on the other hand, reads, translates, and executes the program one line at a time. As an instruction in the program is read by the interpreter, it converts the instruction into machine language and then executes that one instruction. The Python programming language is an interpretive language and uses an interpreter to execute the instructions. The instructions (programs) written by programmers are referred to as source code, which is written using a text editor in an Integrated Development Environment (IDE). IDEs are software applications that include integrated tools for software developers to write, execute, and test software. There are many IDEs available, but they are very similar in the way that they look, are used, and operate. Chapter 1 Computers and Programming 9 Developing Software There are specific phases in the process of developing software that provide for the development of accurate, maintainable, and scalable software, that meets project or program requirements. These phases include design, development, test and integration, and delivery and maintenance. But before any work can begin, a complete understanding of what the program is supposed to do is required. This is derived from the project or program requirements. Requirements The requirements for a computer program detail what the program is supposed perform. How it will do what it is supposed to do will be determined as the design phase is completed during the software development phase (SDP). Requirements Decomposition is the act of discovering in detail from the requirements what the program is required to accomplish. As requirements are reviewed, additional information may be needed and questions may arise. It is important to determine the specifics before moving forward. This process also assists in decomposing the project into manageable “chunks” in terms of the schedule and team assignments for development. Once the requirements are thoroughly understood, the software development lifecycle begins. Software Development Life Cycle (SDLC) The Software Development Life Cycle includes the steps necessary to design, develop, deliver, and maintain the computer program. The phases follow one another and are often accomplished by different team members with collaboration as questions and issues arise. As an example, a software developer may meet with a design engineer to clarify information in the design, or a Test Team member may contact a software developer regarding test results. Software Development Lifecycle Chapter 1 Computers and Programming 10 Design As the requirements are decomposed and documented, the design phase begins, and the break-down of required tasks and logical steps in the program are developed. Design is a very important part of the software development life cycle due to the increased costs of making changes or fixing errors later in the process (errors in code are referred to as bugs). The sooner an issue is resolved, the less rework and testing of the code are needed. This is highlighted in the chart below from the IBM Systems Sciences Institute. Cost of Fixing Errors by Phase Software engineering tools that assist in the design (and development stage as well) include pseudocode (sort of code). Pseudocode is a short-hand version of the order of operations for a program. Consider a requirement for a program that obtains age and salary information from a user, computes Recommended Net Worth, and displays the result. The pseudocode for the solution might be: Step 1 Start the program Step 2 Obtain the age and salary information Step 3 Compute the RNW (age x salary divided / 10) Step 4 Display the output Step 5 End the program Pseudocode Chapter 1 Computers and Programming 11 A flowchart often provides a clearer representation of the algorithm (logical steps to the solution). Various geometric shapes are used to indicate different operations (shapes may vary depending on industry). The order of operations is typically top down, and lines with arrows are used to indicate the order or flow of control. Flowcharts can ensure that steps in the process haven’t been overlooked and that there is a complete understanding of the operational flow of the program. They can also be used to assist programmers when developing a complex part of a program. Example Flowchart A flowchart can be a simple sketch or developed using a flowcharting application such as LucidChart or SmartDraw. Flowcharts are often required to be delivered to a development team or subcontractor together with specific requirements for the code, and are often required in customer documentation. Many software engineers use a combination of tools. Pseudocode may be used for a high-level description of the program or a program area, and a flowchart might be used for more complex sections. Either way, the goal is to have a comprehensive understanding of the requirements at every level to ensure that the final product meets the requirements and is as error-free as possible. Chapter 1 Computers and Programming 12 Development Once a design is complete (or nearly complete since some aspects of the solution may not be knowable during design), the development phase begins. The development phase includes writing the code that will be executed to produce the desired result and meet the requirements. Most often, the development of a program is divided among multiple programmers and requires collaboration and regular discussion to ensure a cohesive solution. To manage software development projects and enable multiple people to work on the same program at the same time, a Configuration Management System (CMS) is used with a source code repository that stores and maintains all of the program files. Software Development Collaboration Programmers access this repository to obtain a copy of a file containing the source code to add functionality or make modifications. The code is written in the copy of the file, and this changed file is tested with the other files in the source code repository. After testing, the modified file is placed into the repository and is used by all of the other programmers in place of the original file. The original file is retained by the configuration management tool as a version control mechanism. If a new file needs to be created, it is created in the configuration management tool and added to the source code repository. CMS tools facilitate collaborative Chapter 1 Computers and Programming 13 development, and version control of the files and the overall project. Many industries and customers require their use. Many configuration management systems have integrated suites that include: scheduling and tracking, task assignment, defect reporting, and issue tracking systems. In addition, tools for software teams and software project managers are commonly used in industry to plan and measure project progress, and to provide visibility into the design, schedule status, cost, and quality of the code. Software Development Processes For the software development phase, the Agile Development Process is a popular method in use today. Agile processes go by various names (a few listed below), but all are iterative and incremental software methodologies. This process of developing portions of the software and adding them to the overall project incrementally is commonly referred to as Iterative Enhancement. Common Agile Methodologies • Scrum – regular meetings, with periodic cycles called sprints • Crystal - methodology, techniques, and policies • Dynamic Systems Development Method (DSDM) • Extreme Programming (XP) • Lean Development • Feature-Driven Development (FDD) Agile Software Development Methodologies A key component of the Agile Development Process is the sprint (the development period between status meetings). Sprint status meetings (scrums) are review and planning events that occur regularly. Tasks completed from the previous sprint plan are reviewed, and completed work is demonstrated to stakeholders for feedback and approval. The tasks that were not completed from the previous sprint plan are reviewed with a course of action (re-plan) for the next development cycle. The scope of new work that will be completed during the next sprint cycle is planned, and engineers are assigned to the tasks. Chapter 1 Computers and Programming 14 The phases in the Agile Development Process include: Plan, Design, Develop, Test, and Evaluate, and are repeated during each sprint. Once delivered, the project would be in the maintenance phase. Agile Development Process Phases Another software development methodology is the Waterfall model which uses similar phases, but they are sequential, and are non-repeating. Each phase depends on the completion of the previous phase, although there may be some overlap. The Waterfall model was used extensively in the past, and is still common in some industries today. The maintenance phase follows the delivery of the software and includes updates. Waterfall Development Process Phases Chapter 1 Computers and Programming 15 Test and Integration As development is completed, the next phase in the software development life cycle is test and integration. In the initial test phase, the programmer runs the program to ensure that there are no errors in the code, and that it performs correctly (meets the requirements). In large organizations, a test team or test engineer will also run the program and report any errors found to the developer for correction. On large-scale programs, a formal Test and Integration Team would be responsible for this phase and would run a variety of tests including: Unit Tests on the modules (portions of code being added or modified), and an Integration Test which verifies that the parts of the program work well together when the new code is integrated into the overall project. Adding the new or modified code into the program may introduce new errors which must be corrected. Regression testing compares new test results with previous results and ensures that the program functions correctly. Types of Errors The three types of errors that are looked for during the test phase are syntax errors, logic errors, and runtime errors. Syntax errors have to do with violating language specific rules like indentation and punctuation and are found by the compiler or interpreter and the code will not execute. The programmer must correct these and most IDEs will highlight them as an aid in development. Logic errors are errors in the algorithm or the way that the algorithm was written by the programmer. For example, if the requirement is that the program multiply a number by two only if it is greater than ten, and the programmer writes the code so that a number is multiplied by two if it is less than ten, that would be a logic error. The program compiles and runs, but it produces incorrect results. Runtime errors are logic errors that cause the program to stop executing. An example would be a part of the program attempting to divide a number by zero. Most IDEs will provide a Traceback of the sequence causing the error. Runtime errors can be avoided by thoroughly designing and testing the algorithm. Chapter 1 Computers and Programming 16 Delivery and Maintenance The final phase of the software development life cycle is the delivery and maintenance phase. In this phase, the program is delivered to the client or customer and a period of maintaining the program begins. Maintenance of a program would include updates that fix errors or security issues found after initial delivery, or upgrades that provide additional functionality or capability. Updates to software programs are commonplace today. Ergonomics The set-up or arrangement of the computer and furniture to minimize the risk of injury or discomfort is a field of engineering called ergonomics. It includes the study of the physical effects of repetitive motion and working in a stationary position for an extended period. As more people spent their days working at computers, a variety of health issues surfaced. Some guidelines include: • Monitor position – with respect to eye level (dry eyes) • • Adjustable chair – arm posture (tennis elbow) • • Elbows should be at 90-degree angles Proper posture – back posture (lumbar issues) • • Eyes should be looking slightly downward Lumbar support and back straight Taking periodic breaks – eye strain, posture, repetitive motion • 20-20-20 rule says every 20 minutes look 20 feet way for 20 seconds • • Standing or walking away for few minutes Adequate lighting – eye strain • Dark areas and dark backgrounds cause eye strain Ergonomic Guidelines Chapter 1 Computers and Programming 17 Chapter 1 Review Questions 1. Computers are simply _________ __________ devices. 2. The physical parts of the computer are referred to as _____________. 3. The CPU is considered the ___________ of the computer. 4. The CPU performs basic ____________ and controls computer _________. 5. Main memory (RAM) is ________ and is erased when a computer is turned off. 6. __________ Storage device memory is non-volatile and is retained when the power is turned off. 7. A computer keyboard, mouse, and camera are examples of _________ devices. 8. Computer monitors, speakers, and printers are examples of __________devices. 9. Sets of programmed instructions for a computer are referred to as __________. 10. _____________ and _____________ are the two basic types of software. 11. The language of computers is a _________ language. 12. The smallest information representation in computing is a _____ or binary digit. 13. A binary digit can have a logical state of _____ or _____. 14. A Byte is a combination of ________ bits that are either one or zero. 15. The number represented by 0110 1001 is _______. 16. The binary representation of the number 255 is ___________. 17. The names of the two low-level languages are __________ and __________. 18. A Machine cycle consists of ________, ________, ________, and ________. 19. A 2 GHz (gigahertz) processor can execute __________ instructions per second. 20. High-level languages make programming a computer _____ and more _______. 21. Java is a _______ -level language. 22. A (n) ___________ translates a high-level language into a separate machine language program. 23. A (n) ___________ reads, translates, and executes a program one line at a time. 24. The four steps in the Software Development Life Cycle are ________, ____________, _______________, and _________________. 25. The costs associated with fixing errors in code are __________ when caught early in the process. Chapter 1 Computers and Programming 18 26. A written shorthand version of the steps to complete a task in a computer program is called _______________. 27. The act of discerning in detail from the requirements what the program is to accomplish is called ___________________ ____________________. 28. A set of logical steps taken to complete a task is called a(n) _____________. 29. Plan, design, develop, test, and evaluate are the five steps in the ___________ development process. 30. The three types of programming errors are _________, __________ and ____________ errors. Chapter 1 Short Answer Exercises 31. Explain the major difference between main memory and secondary storage. 32. List at least three (3) input devices. 33. List at least three (3) output devices. 34. List the two (2) types of software. 35. Write the word Java using the binary representations of the letters. 36. Write the binary representation for the number 176. 37. List the two low-level languages. 38. What is the purpose of a source code repository? 39. List the five phases of the Agile Development cycle. 40. Explain the difference between logic and syntax errors. Chapter 1 Programming Exercises 41. Write the pseudocode for the steps required to determine the total price for some number of items entered by the user priced at $9.00 each with a 7% sales tax. 42. Draw a flowchart of the steps in Programming Exercise 1 above. 43. Ensure that you have access to a copy of Eclipse (ref. Appendix B). Chapter 1 Computers and Programming 19 Chapter 2 Java Language Basics The Java programming language was initiated as a project in 1991 by James Gosling, Mike Sheridan, and Patrick Naughton, and was originally designed for embedded systems. With the introduction of web browsers, and the reduction in prices and speed increases for computers in the 1990’s, Java developed into a general-purpose programming language with the release of version 1.2 (Java 2) in 1998. The current version is Java SE13 released in September 2019. Java is a class-based, object-oriented language that is compiled to bytecode and runs on any virtual machine. JVM - The Java Virtual Machine (JVM) enables computers to run Java programs. The JVM converts Java bytecode into machine language, manages memory, and is part of the JRE. It allows Java programs to run on most devices and operating systems. JDK - The Java Development Tool-kit (JDK) is a development environment for creating Java programs and applets that includes the JRE, an interpreter, compiler, archiver, and documentation generator. There are a variety of JDK’s for different operating systems and environments available. JRE - The Java Runtime Environment (JRE) is an implementation of the Java Virtual Machine that executes Java programs. Chapter 2 Java Language Basics 20 The Eclipse IDE The Eclipse IDE provides all of the Java development tools necessary to develop programs in Java. It is the most widely used IDE for Java programming, is used by many companies, and is suitable for starting out in Java as well as advanced programming and collaboration. It is free to download and use, and is similar to most IDEs in look-and-feel and capability. The Eclipse version used in this text is 2019-06. Obtaining a copy is covered in Appendix B and Getting started in Eclipse is covered in Appendix C and should be completed before continuing. The Eclipse IDE Parts of a Java Program The “Hello World” program from the appendix is repeated below with line numbers for explanations of the parts. On line 1 is the package or project name. The package in Java is used to group related classes and files. On line 3 is the class name for the program. Every Java program has at least one class. The word public is an access specifier indicating that the class is publicly accessible for use. Other access specifiers will be covered later. Chapter 2 Java Language Basics 21 The brace following the class name on line 3 begins a block of code for the class. The closing brace for the class is at the margin on line 10 and aligns vertically with the word public preceding the class. Aligning braces with the block of code that they close is important for readability and the IDE will automatically align and indent them. Line 5 is the header for the main method for the program. This is where execution of the program begins when it runs. Note the brace at the end of the line which begins another block of code. The closing brace is on line 8 and is aligned with the indented header for the main method (the word public). The parts of the main method header are: • public – specifying that it is accessible outside the class • static – designation that it is a class method and not associated with any object • void – indicating that it has no return value • (String[ ] args) – a provision for command line arguments Line 6 is a comment added by Eclipse indicating that the main method was automatically created as a result of the checkbox when the class was created. Line 7 is an output statement executed by the program. This line ends with a semicolon which is the end-of-line marker in Java. To the compiler, a semicolon indicates the end to a statement just as a closing brace indicates the end of a block of code. Chapter 2 Java Language Basics 22 Syntax and Grammar Each programming language has some characteristics and rules that must be followed when writing programs in that language. Two of these are the syntax and grammar of the language. The syntax of a language refers to the rules for properly combining symbols, operators, and punctuation, as well as the proper use of operators. The grammar of a programming language determines the structure of the sentences containing the symbols, operators, and punctuation that make up the instructions for the computer. Another characteristic of programming languages is the use of keywords or reserved words. Keywords are reserved by the language for a specific use and cannot be used for another purpose. Eclipse will display them in a color font to highlight them as shown below (package, public and class). The following is a list of some of the Java keywords. boolean catch char class double else extends final finally for if implements import int new package private public return static String throw try void while Java Keywords (partial list) Note: True, false, and null are literals and are reserved in Java as well. Comments In addition to the tools mentioned in Chapter 1 for designing and developing software, comments within the code can be helpful and are often required. Chapter 2 Java Language Basics 23 Comments in programs are lines of code that are not executed, and are ignored by the compiler. They are provided for human readers, and are used to clarify values or sections, or explain complex operations. This is important because most software is maintained, updated, and expanded. Code is written once, but is read many times, and the person who wrote the code may not be the person making the modifications, or the person who wrote the code may not remember why a section was written a certain way or why a specific value was used. Adding comments to code while it is being written can save hours of reading through the lines later when the code is being changed. Comments can also be used as a development tool. Pseudocode can be written in the edit window as a comment to act as a place-holder or reminder that will be replaced later by actual code. Single line comments in Java begin with two forward slashes. The Eclipse IDE used in this text will color code comments in green font as the default. For multiline comments, a forward slash with an asterisk “/*” begins the paragraph and an asterisk forward slash “*/” ends the paragraph. For the Javadoc documentation generator, which creates HTML documents from Java source code, the opening paragraph indicator is a forward slash and two asterisks “/**” and it ends the same as the multi-line comment. // a single line comment in Java /* a multiline comment in Java */ /** A Javadoc comment for the document generator */ Java Comment Types Variables Variables are elements in programs that are used to allocate memory and store information that the program will use. They are called variables because what is stored in them can vary as the program runs. A variable is declared and named Chapter 2 Java Language Basics 24 by the programmer to allocate memory for use by the program. The computer remembers the memory address of where it is stored, and the programmer refers to it in the program by the name that was used to declare it. In the Hello world program, a literal string (sequence of characters) was passed to the output statement. A variable could also be used as shown in Ex. 2.1 below. In the example, a String variable is declared on line 7 and is assigned the value “initially”. This is referred to as initializing the variable. The equal sign is the assignment operator in Java and is used to assign a value to a variable. The computer allocates memory for a String named myWord and stores the value “initially” there. On line 8, the variable is passed to the output statement. The variable is then assigned “currently” on line 10 which replaces the value that was previously stored and line 11 displays it again. The Eclipse console output is shown below the program. The use of println() instead of print on lines 8 and 11 causes the output to be on separate lines. Ex. 2.1 – String Variable Declaration, Initialization, and Modification Variable Declaration and Utilization Notice in the example that when the variable myWord is assigned a new value, it is not preceded by the word String. String is the data type (covered next) of the variable which is only used when a variable is being declared. Chapter 2 Java Language Basics 25 Data Types The example in Ex. 2.1 declared a String variable and assigned it a value that was a literal string (a series of characters within double quotes). When a variable is used to store a number, a different data type is declared. The data types in Java include int for integers (whole numbers), and float and double for floating-point numbers (numbers with a decimal). The data type tells the computer how much memory to reserve for the variable. To store an integer, or float, 4 bytes are allocated. To store a double, 8 bytes are allocated to accommodate more precise numbers (the double data type is recommended for fractional numbers). The numeric ranges for integers and doubles in Java are sufficient for most program requirements and are used for whole and fractional numbers in this text. Table 2.1 below lists some of the basic data types used in Java. Table 2.1 - Java Primitive (simple) Data Types The next example declares two integer variables and uses them in three different output statements to highlight some additional considerations when working with numbers in Java. Each of the output statements uses println() which adds a line feed after the output is displayed. The first output statement adds the two Chapter 2 Java Language Basics 26 values of the variables, but the second does not. The difference is the occurrence of the literal string that precedes the expression. This causes Java to interpret the plus sign as adding textual output and not numbers. Note that num1 could not be mathematically added to the literal string. The value stored in num2 could be added to num1, but the individual values are displayed. The third output statement forces the addition of the values using parenthesis. Ex. 2.2 – Numeric Variable Declaration, Initialization, and Output Program Output Variable Names The variable naming convention most used in Java is called uppercasing. A single word variable is all lower case, and a two-word variable has the first word in lower case and the first letter of the second word in uppercase. This aligns with W3C (World Wide Web Consortium) as well as other Guides and Standards for the language. When naming variables, there are a few rules that need to be followed: • none of the Java keywords can be used as a variable name • there cannot be any spaces in the name • the first character must be a letter (or an underscore) • uppercase and lowercase letters are distinct Chapter 2 Java Language Basics 27 In addition, the name of a variable should describe the data that it stores. Software engineering principles and programming standards require descriptive variable names to enhance readability. A longer name is usually better. Using variable names like var or pd are ambiguous and make removing errors (debugging) and maintaining the code more difficult. If a comment is needed to describe a variable, then the name of the variable is inadequate. Table 2.2 below lists some examples of good and bad variable names. Table 2.2 - Variable Naming Error Notifications Java is case sensitive and common programming errors include case errors and misspelling a previously declared variable name. These types of errors will be highlighted in most IDEs as they are introduced so they can be corrected immediately. If errors exist in the code and an attempt is made to run the program, it will cause a compiler error and will not run. In the error example below, the variable number is declared with all lowercase letters, but an uppercase letter is used in the output statement. The IDE underlines the variable name with red and places an error indicator at the margin on the line containing the error. Hovering over the indicator provides a description of the error. Chapter 2 Java Language Basics 28 When an attempt is made to run the program, a compiler error is output to the console area of Eclipse with a description and line number containing the error. Error Example Variable Assignments When a variable is declared, it is typically assigned an initial value. This is referred to as initialization. A single equal sign is the assignment operator, and the variable being assigned is on the left side of the operator. The right side of the assignment operator can be a value or an expression. In this statement, a variable userAge is declared as an integer, and is assigned the value 29. int userAge = 29; // userAge is assigned 29 As shown previously, a variable can be changed while the program is running. The new value assigned to a variable overwrites the old value in memory where the variable is stored. Ex. 2.3 – Changing the Value Stored by a Variable Chapter 2 Java Language Basics 29 In Ex. 2.3, a variable is declared and initialized. The variable is then changed using the old value in the expression to assign a new value. Note that a variable can be on both sides of the assignment operator. The right side is evaluated first by the computer and the result is assigned to the left side. Constant Variables (Named Constants) A constant is a variable that cannot be changed by the program, must be initialized when declared, and cannot be assigned a new value. There are several situations when this is preferred. One is to eliminate the use of unidentified numbers in programs, and another is to ensure that a specific value is used throughout the program. An unidentified number in programming is referred to as a magic number. They are literal numbers in a program without an obvious meaning. When a program is being modified and an expression uses a magic number, it may be difficult to determine what the number means even by the original programmer. As an example, the following line appears in a program that declares a double as diameter, but the meaning of 3963.2 is unknown. Since the equation results in a diameter, it appears to be a radius. It isn’t clear. By using a named constant in the code, the meaning is clear. The constant is declared and initialized and then used in place of the literal number wherever it is needed in the program. Constants are declared using the final keyword followed by the data type, name, and initialization. The standard for naming constants is all uppercase letters with underscores between words. Named constants are also used to ensure that the same value is used throughout the program and by all programmers. If multiple programmers are working on a program that calls for them to use the radius of the earth in various equations, they can use a named constant to ensure that the same value is used. The earth is not a sphere and there are multiple values for its radius. Chapter 2 Java Language Basics 30 Named constants also prevent typographical errors when the same value is being used multiple times. In addition, when a new value is needed for the constant, the change is made in a single place in the code. As an example, a scientist overseeing a program using EARTH_RADIUS may decide that the equatorial radius being used in the program should be changed to the pole radius of 3950.0. It will only need to be changed to the new value in one place in the code. This eliminates the possibility of typographical errors or missing an occurrence when updating all of the equations that use the value. Global Variables A global variable is a variable that is declared outside all methods including the main method. This makes them accessible to all parts of the program. Most programming standards do not permit their use except when they are global constants, because they could be changed arbitrarily by any part of the program making debugging very difficult. Since a constant cannot be changed, a global constant provides for using a consistent value across all of the code in a program. Java doesn’t explicitly have global variables since every variable must belong to a class, but once declared, they can be accessed using the class name. Mathematical Operators and Expressions The operators for mathematical expressions in Java include: addition (+), subtraction (-), multiplication (*), division (/), and the modulus operator (%). Table 2.3 - Arithmetic Operators Chapter 2 Java Language Basics 31 The mathematical operators combine with variables and expressions in programs to perform operations. The lines of code in Ex. 2.4 declare three integers and use them in various equations. Recall that the computer evaluates the right-hand side of the assignment operator, and then assigns the result to the left-hand side. Ex. 2.4 – Mathematical Operators The results from division in Java are different for different data types and data type combinations. If one of the values is a floating-point number (number with a decimal), the result is a floating-point number. If both numbers are integers as in the first example below, the result is truncated to an integer and the decimal portion is discarded. One way to remember this is “int divided by int is an int”. However, an integer divided by an integer will result in a double if the variable it is assigned to is declared as a double. The modulus operator produces the remainder after division (sometimes referred to as modulo divide). The operand on the left of the operator is divided by the operand on the right and the result is the remainder after division. Chapter 2 Java Language Basics 32 Precedence in Java is parenthetical expressions first, followed by multiplication, division, modulo division, and lastly addition and subtraction. Operators with the same precedence are handled left to right, and precedence can be forced using parenthesis. The use of parenthesis is often preferred even when they align with precedence. This enhances the readability of the expression and helps to eliminate errors. The equations in the table below are the same, but the results are quite different. Table 2.4 - Precedence and Parentheses Mixed-type expressions are promoted to the higher data type in use. In an expression with an integer and a double, the integer is temporarily converted to a double, and the expression is promoted resulting in a double. The same rule applies to an expression with an integer and float. When using floating-point (fractional) numbers, the double data type is recommended over float for variables since it is more precise as the results below illustrate. Chapter 2 Java Language Basics 33 Programming Algebraic Expressions When converting mathematical expressions into Java code, the translation may require adding operators and parentheses to ensure the correct result. As an example, the expression 3xy in algebra would produce a syntax error. The multiplication operator must be inserted as in 3 * x * y. When an expression contains fractions, precedence requires careful consideration to ensure that operations occur in the correct order. With extremely complex equations, breaking the expression into parts may be the best course of action. Conversion examples: Converting Algebraic Expressions Math Methods The Java Math library contains constants like PI and methods for exponentiation, rounding numbers, and other common operations. To use these operations, the method is preceded by the library name “Math” as shown below. The functions are passed arguments which are values passed to methods and functions for their use. As an example, for rounding numbers, Java has a Math.round() function. The line of code below passes the number 9.4 as an argument to the round function. The function executes and the result is assigned to the variable. Chapter 2 Java Language Basics 34 For operations with exponents, the Math.pow() function is used. In this case, two arguments are required. The first argument is the number to be raised, and the second is the exponent. In addition to the round() and pow() functions, the java.lang.Math library contains functions for performing other mathematical operations including: abs(x), acos(x), asin(x), atan(x), cos(x), hypot(x), log(x), sin(x), sqrt(x), and tan(x) among others. Below is an example that uses the square root function. Converting Data Types Converting from one data type to another in code is referred to as casting. The round method in the example below returns a double, which is then cast to an integer so that it can be assigned to the integer variable roundInt. The data type that the value is being cast to is in parenthesis. Obtaining Keyboard Input To obtain input from the keyboard in Java requires a Scanner. To use a Scanner, the class java.util.Scanner must be imported. Import statements are located between the project package and the class, and provide access to Java libraries. Ex. 2.5 – Keyboard Input Chapter 2 Java Language Basics 35 The line of code below declares a Scanner named in (can be any appropriate name) and assigns it a Scanner using “new” and “System.in” which is the standard system input source (the keyboard). When a program needs to obtain keyboard input, a prompt is used to describe the input being requested. Once the requested data is entered, the user will press the Enter key. To obtain the input, a variation of the next() method is used. In the example below, the prompt requests a number and nextInt() is used which reads an integer. Note that nextInt() is preceded by the name of the scanner and the dot operator to access the method. When the program runs, the prompt is displayed and the program waits. Once a value is entered in the console area of Eclipse and the Enter key is pressed, nextInt() will obtain the value and it will be assigned to the variable. After the output statement, the Scanner is closed (a recommended practice). Obtaining Keyboard Input The Scanner has methods to obtain input for various data types. During the design phase of the program, different approaches and methods should be considered depending upon how the data will be used. different versions of the method are shown below. Chapter 2 Java Language Basics Examples using the 36 Scanner Methods for Obtaining Input Design Consideration The next() method will read input until whitespace is encountered. Whitespace can be a space, tab, or line feed. Consider a program that requires the user to enter the name of a city. If the city name entered is Denver, then next() will read the full name. If the name of the city is New Brunswick, then next() would only read the word New. In this situation, using nextLine() would ensure that the entire city name would be read. Formatting Output The print() function that was used in previous examples to display output has two other versions. One version, println() adds a line feed after the output is displayed. Ex. 2.6 – Line Feed Output Program Output Chapter 2 Java Language Basics 37 The other version for output is printf() which is used when formatting output. A format specifier is used to indicate the formatting to be applied. Arguments are passed to the function: the format specification(s) in quotes, and the value(s) or string(s) to be formatted. The specifier begins with “%”, is followed by the formatting, and ends with the type: “f” (float), “d” (integer), and “s” (string). An integer is placed after a decimal in the specifier for the number of decimal places. In Ex. 2.7 below, three different decimal specifiers are used. Note that using printf() eliminates the ability to use println(), so line feeds are added as separate output statements in the example. Ex. 2.7 – Formatted Output Program Output Previously the “+” operator was used in output statements that combined text with numeric values. With format specifiers, a comma separates the specifier and the variable as shown in Ex 2.7. A decimal place specifier that is fewer than the number to be formatted will cause rounding as shown in the example. Chapter 2 Java Language Basics 38 When a literal String is part of the output, the format specifier can be located within the same quotes as shown here. When more than one variable is included in the output, the specifiers are included in the string portion in the order in which they are to be used in the output. The actual variables are included afterward as shown here. Notice that the numbers in the output were rounded due to specifying two decimal places. To add commas for large numbers, a comma is included in the specifier after the percent sign. Other formatting techniques and methods will be covered later in the text. This line of code adds the dollar sign to the output. Chapter 2 Java Language Basics 39 Numeric data is often output in columns and right-aligned. To designate a specific amount of space to use for output, the number of spaces is added to the format specifier before the decimal or designator if no decimal is used. A negative sign before the spacing value is used for left alignment of the output. In Ex 2.8, the descriptions are left-aligned and the prices are right-aligned. Ex. 2.8 – Specifying Alignment and Output Spacing Program Output In Ex. 2.8, the word “Beverage” used all of the allocated space. If a String or value does not fit in the specified space, the item will still be displayed entirely but without any spaces. Escape Sequences To insert certain characters and formatting within literal strings, escape characters are used. The escape sequences include: new line “\n”, tab “\t”, Chapter 2 Java Language Basics 40 double quote \”, and back slash “\\”. The sequence is surrounded by quotes unless it is within a literal string. When println can’t be used because printf is being used, a line feed can be inserted as “\n” anywhere a line feed is needed. Table 2.5 - Escape Characters Ex. 2.9 – Escape Sequences Strings A string is a sequence of characters. When a literal string is written in the code, it is surrounded by double quotes and is referred to as a string literal. A String variable is the String object in Java and can contain a large amount of text Chapter 2 Java Language Basics 41 (2,147,483,647 characters). A character is a data type that can store a single character. It is declared using char and is assigned using single quotes. A String can contain a single character, but is always surrounded by double quotes. Characters are stored using their ASCII numeric values, so the assignment statement above would actually store 65 as the value for “A” (see Appendix A). The computer knows that the data type is char and handles the translation. The characters contained in a String are in positions called indexes beginning with index zero. In the String below, the “e” is at index 3 although it is the 4th letter in the word. To obtain a character from a String the charAt() method is used and is passed the index of the character to obtain. Note that the method is preceded by the String variable’s name and the dot operator (or dot notation). In the code below, the character “e” would be assigned to the char variable letter. To obtain a portion of a String, the substring() method is used. When two arguments are passed to substring(), the first argument is the index of the starting point of the substring to obtain, and the second argument is one index beyond the portion to obtain. As an example, the following statements assign “friend” to the String variable portion. Chapter 2 Java Language Basics 42 When one argument is passed to substring(), the argument is the index of the starting point of the substring to obtain, and the ending point is the end of the String. The following statements assign “car” to the String variable ending. Strings also have a method for obtaining their length. The length() method returns the number of characters in a String including any spaces. In the code below, 8 would be assigned to the variable len. Remember that the indexes for the characters are 0 through 7, one less than the length. Combining two or more Strings is referred to as concatenation. operator is used to concatenate Strings. The “+” The operators will not add spaces between the Strings. They are simply joined together as shown in Ex. 2.10 below. Ex. 2.10 – String Concatenation To add a space between the Strings, it can be added to either of the Strings being combined or separately as shown here. Chapter 2 Java Language Basics 43 The lines of code in Ex. 2.11 below prompt for a first and last name, and use the next() method to obtain the input. The inputs are stored in Strings, and concatenation is used in the output statement to add a space between the names and to add a period at the end. Ex. 2.11 – String Concatenation The ability to manipulate Strings is an important skill in programming. Most interfaces receive input as Strings and perform error checking and conversion of numeric values. Some of these techniques are covered in the next chapter. Methods, Functions, and Dot Notation In this chapter, the examples used methods and functions to perform operations. Although the terms tend to be interchangeable, for clarification, a method typically refers to functionality associated with an object of a class, and a function is not. As an example, the String variables declared in this chapter are declared using an upper case “S” whereas the integer and double data types are not capitalized. Classes are capitalized in accordance with programming standards, and the String is a class. The String class has other methods available including toLower() and toUpper() for converting. To use them, the variable name Chapter 2 Java Language Basics 44 for the String is followed by the dot notation and the method name. In the statements below, a String is declared called word. The variable is actually an object of the String class and inherits the methods of that class. The methods are accessed using the dot operator as shown on the line below that uses length(). The Scanner is also a class that provides methods some of which were used in this chapter. Again, after declaring a Scanner, dot notation was used to utilize the methods. The Math functions that were used did not require declaring a Math object before using them, but did use dot notation. The Package (Library) name Math, the dot operator, and the function name were used as shown here. Classes and Objects are covered in a later chapter. Programming Style and Standards Proper programming style and format of the code make a program easier to read and maintain, and help to prevent errors from being introduced. The cost to fix errors increases dramatically as the software development cycle progresses. Anything that decreases the chances of introducing bugs is welcome and utilized. For these reasons, Programming Standards have been developed to provide uniformity and enhance the readability and maintainability of code. They include proper spacing and indentation among others. An entire program could be written on a single line and the computer would have no problem with it, but someone trying to debug the code or add functionality would have a very difficult time. Appendix G contains a set of Programming Standards for Java. Programming Standards and Style Guides are used in industry to ensure the readability and maintainability of programs due to the time and cost associated with poorly written and ambiguous code. Chapter 2 Java Language Basics 45 Chapter 2 Review Questions 1. The characteristics and rules that must be followed when writing programs in a high-level language are ___________ and ___________. 2. Words that are reserved in a programming language are called ____________. 3. Words added to programs to explain complex areas or to add clarity and are not executed when the program runs are _______________. 4. __________ are used in computer programs to store values in memory. 5. The __________ data type is used to store whole numbers. 6. Numbers with a decimal should be stored in the _________ data type. 7. The equal sign is used to ______________ a value to a variable. 8. The ______ side of the assignment operator is assigned to the ______ side. 9. A variable must be __________ before it can be used by the program. 10. Variable names (can or cannot) _______ begin with a number. 11. A ___________ should be used in place of a magic number. 12. A value passed to a method is called a(n) ___________ . 13. The __________ escape character is used to produce a tab. 14. Converting an item to a different data type is known as ___________. 15. Errors in programing are typically referred to as __________. 16. Which of the following variable names follow proper naming conventions? a. b. c. d. e. average 8pieces netPay$ grossPay hourlyRate 17. The first character in a String occupies index ________ in the String. 18. The _________ data type can store one character. 19. Concatenation refers to _____________ two or more Strings. 20. Programming _____________ provide uniformity and enhance the readability and maintainability of code. Chapter 2 Java Language Basics 46 Chapter 2 Short Answer Exercises 21. What type of variable is defined in this expression? final double INTEREST_RATE = 0.07; 22. What do the following lines of code display? double ouncesPerCan = 8.0; System.out.print(ouncesPerCan); 23. What is the resulting output when the following lines of code are executed? int number = 23; number = 52; System.out.print(number); 24. What do the following lines of code display? int number = 12; number = number + 8; System.out.print(number); 25. What value is assigned to num3 in the lines below? int num1 = 32, num2 = 6; int num3 = num1 + num2; 26. What do the following lines of code output? double num1 = 2.5; int num2 = 5; num1 = num1/num2; System.out.print(num1); 27. In these expressions, what value will be assigned to the variable result? a. result = 5 / 2.0; b. result = 7 / 2; c. result = 4 * 3 / 2; d. result = 5 % 2; Chapter 2 Java Language Basics 47 28. Express the following equations using Java expressions. e. 4xy f. z = 2ab g. y = b2-4ac 𝑎+𝑏 h. 𝑡 = 𝑥 − 𝑦 29. In the expressions below, what will be the value assigned to the variable num1? a. num1 = Math.round(2.3); b. num1 = Math.pow(4,2); c. num1 = Math.sqrt(25); d. num1 = Math.sqrt(Math.sqrt(81)); 30. In following statement, what does the number “8” specify? System.out.printf(“%8.2f”, number); 31. After the lines below execute, what will be the output? double number = 123.453; System.out.printf(“%.2f”, number); 32. What is the output from the following statement? System.out.print(“She said \”hello\”.”); 33. After the lines below execute, what will be stored in the variable name? String first = “Angela”; String init = “P.”; String last = “Harad”; String name = first + “ “ + init + “ “ + last; 34. After the lines below execute, what will be stored in the variable letter? String name = “Sheila”; char letter = name.charAt(1); Chapter 2 Java Language Basics 48 35. After the lines below execute, what will be stored in the variable part? String word = “cartoon”; String part = word.substring(0, 4); 36. After the lines below execute, what will be stored in the variable portion? String word = “classroom”; String portion = word.substring(5); 37. After the lines below execute, what will be stored in the variable len? String cafe = “Angelo’s”; int len = café.length(); 38. Which of the following should be used to read a line of text including spaces to store in the variable phrase? a. phrase = in.nextInt( ); b. phrase = in.nextDouble( ); c. phrase = in.nextLine( ); d. phrase = in.next( ); Chapter 2 Programming Exercises 39. Complete the “Hello World” exercise in Appendix C and provide a screen capture of the IDE with the output. 40. Write a line of code that displays the following text. Java is a high-level language. 41. Write a line of code that displays the following text with the quotes. The waiter said “The special is good!” 42. Write a program that prompts the user to enter their name, stores the input in a String variable, and then displays ‘Hello ‘, and the name that was entered. Chapter 2 Java Language Basics 49 43. Write a program with three integer variables: first, second, and third. Assign the values 5, 6, and 7 to the variables and display each on a separate line using the variable names. 44. Write a program that declares the constant below and displays “The interest rate is “ followed by the constant and a percent sign. INTEREST_RATE = 7 45. Write a program that assigns the variable tickets the value 125 and then displays “The tickets sold today were “ followed by the variable. 46. Write a program that defines three String variables named word1, word2, and word3. Assign abc to word1, def to word2, and then assign word1 and word2 combined to word3 using concatenation. Then display word3. 47. Write a program that uses a double that is assigned 12345.678 and use a format specifier to display the number with commas and two decimal places. 12,345.68 48. Write a program using variables to display the numbers below on separate lines, with two (2) decimal places, and in fields that are eight (8) characters wide. 123.45 1452.56 56.80 49. Write a program that uses three (3) print statements to display the words No, lines, and between all on one line with spaces between the words. 50. Write a program that prompts the user to enter their age, stores the age in a variable named age, and then displays “Your age is “ and the age that was entered. 51. Write a program that prompts the user to enter a number, and then a second number. The program will add the numbers, store the result in a variable and display “The sum of the numbers is: “ and the result. 52. Write a program that computes the total cost of a meal based on the meal price entered by the user, plus a 20% tip, and 5% sales tax. The output should be displayed as shown below and include a dollar sign and two (2) decimal places. Chapter 2 Java Language Basics 50 53. Expand number 14 to include output of the tip, and tax amounts, before the total price. The output should include a blank line between the input prompt and the output, dollar signs, two (2) decimals, and amounts aligned right. 54. Write a program that prompts the user to enter a Fahrenheit temperature, computes the Celsius temperature, and displays ”The Celsius temperature is: “ and the result. The equation for the conversion is: C = (F – 32) / 1.8 Test data: When F = 23, C = -5 55. Write a program that prompts the user to enter the lengths of the two sides of a rectangle. The program will compute the area and perimeter, and assign the values to two variables. Then display the computed values with their titles as shown in the example below. 56. Write the pseudocode for a program for a Yogurt vendor that computes the total sales and profit for a day’s sales based on the number sold at $6.50 each, and the cost of the Yogurt to the vendor which is $4.25 each. The profit is the total sales minus the total cost. 57. Write the program for the Yogurt vendor in #56 above. The program will display the output as shown in the example below. Note the dollar signs and alignment. Chapter 2 Java Language Basics 51 58. Write a program that prompts the user for two integers (x and y) and computes a result using the equation below. Note the output when y is entered as 1. 𝑎𝑛𝑠𝑤𝑒𝑟 = 𝑥+2 𝑦−1 59. Part #1: The surface area of a sphere is given by the equation below. Write a program that prompts the user for the radius of a sphere as a double and the units of measure (feet, miles, etc.), computes the surface area, and displays the result with the square units. Use Math.pow() in the solution, and format the output to 3 decimal places. Use 3.14159 as the value for PI. Surface area = 4 π r2 Part #2: The volume of a sphere is given by the equation below. Write a program that prompts the user for the radius of a sphere as a double and the units of measure (feet, miles, etc.), computes the volume, and displays the result with the units. Use 3.14159 as the value for PI. 𝑉𝑜𝑙𝑢𝑚𝑒 = 4𝜋 𝑟3 3 Part #3: Combine parts 1 and 2 into a single program and add the computation and output for the circumference. The program will prompt the user for a radius as a double and the units of measure. Two examples are provided using 3.14159 as the value for PI, for testing to validate the output. 𝐶𝑖𝑟𝑐𝑢𝑚𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 2𝜋𝑟 Volley Ball radius: approx. 4.1 inches The Earth’s moon radius: approx. 1,080 miles (note the commas in the output) Chapter 2 Java Language Basics 52 Chapter 2 Programming Challenge Loan Calculator Design and develop a program for a car dealer that computes the monthly payment, total payback amount, and total interest paid for a car loan based upon the loan amount, interest rate, and loan duration in months. The equation for determining the monthly payment for a loan is: Monthly Loan Payment Formula: MP = L * ( r / (1 - (1 + r)-N)). o MP = monthly payment amount o L = principal, meaning the amount of money borrowed o r = effective interest rate. Note that this is usually not the annual interest rate (see below). o N = total number of payments Calculate the effective interest rate (r) - Most loan terms use the "nominal annual interest rate", but that is an annual rate. Divide the annual interest rate by 100 to put it in decimal form, and then divide it by the number of payments per year (12) to get the effective interest rate. Note that the user enters the interest rate as a percentage (4 for 4%). o Example, if the annual interest rate is 5%, and payments are made monthly (12 times per year), calculate 5/100 to get 0.05, then calculate the rate: Effective rate = 0.05 / 12 = 0.004167. Sample output: Chapter 2 Java Language Basics 53 Chapter 3 Decision Structures and Boolean Logic Decision structures determine the statements that execute based upon a conditional expression that is used to determine whether or not a line or lines of code execute. Decision structures provide multiple paths through a program based on the status of a true or false condition. If the condition is true, then a statement or statements are executed, otherwise they are not executed. The if Condition As an example, assume that a Theater has seating for 400 customers. Once the Theater has sold 400 tickets, the show has been sold out. When this occurs, the Theater displays a “Sold Out” sign at the box office. The decision to display the sign is made based upon whether or not 400 tickets have been sold. The decision structure is implemented using the if statement. Ex. 3.1 – Conditional Statement Pseudocode If 400 tickets have been sold - Display the “Sold Out” sign The condition tests if 400 tickets have been sold, and if it is true, the “Sold Out” sign is displayed. If the condition is false and 400 tickets have not been sold, then the sign will not be displayed. Chapter 3 Decision Structures and Boolean Logic 54 Conditional expressions are represented in flowcharts as diamonds. The different paths that the program can take are shown using lines from the corners of the diamond, arrows indicate the direction, and text indicates the result. These paths in the program are often referred to as the Flow of Control or the Order of Operations. In the example, if the condition is true then the flow of control follows the path to display the sign. Otherwise (if the condition is false), the program continues without displaying the sign. Conditional Expression Flowchart When programming a conditional expression in Java, the syntax includes parenthesis around the conditional expression, and braces to enclose the statement(s) executed when the condition is true. The statements to be executed are indented for readability (most IDEs automatically indent these lines). The general format is shown below with the opening brace on the line with the condition. Some programmers place the opening brace on the line following the expression, however most Java Style Guides prefer the format shown here. Ex. 3.2 – Theater Ticket Sales “if” Condition (note the use of two equal signs) Chapter 3 Decision Structures and Boolean Logic 55 When multiple statements are associated with a condition, they form a block of code. A block of code is a group of associated statements. In this case, they are associated with the conditional expression. If the condition is true, all of the statements within the braces (the block of code) will be executed. If the condition is false, all of the statements within the braces will be skipped over. Continuing the Theater example, assume that when the show is sold out, the box office is closed in addition to the sold-out sign being displayed. A standard practice is to indent the pseudocode the same way that the lines would be indented in the actual code. If 400 tickets have been sold - Display the “Sold Out” sign - Close the box office The flowchart for the Theater example has been modified to include closing the box office if the condition is true. Note how clearly the pseudocode and flowchart indicate the path taken if the condition is true. The modified code is shown in Ex. 3.3 below. Chapter 3 Decision Structures and Boolean Logic 56 Ex. 3.3 – Theater Ticket Sales “if” Condition Expanded Boolean Expressions Conditional expressions are either true or false, and are referred to as Boolean Expressions named after the mathematician George Boole (1815-1864). Boolean expressions are implemented using Relational Operators that resolve to either true or false by testing relationships. The result of the expression determines the next step or path for the program. For example, one value can be greater than another, or less than another, or equal to another. One of these three cases must be true, and the others would be false. Table 3.1 lists the Boolean operators available in Java. Note that two equal signs are used to test for equivalence (a single equal sign is the assignment operator). Table 3.1 – Relational Operators Some examples follow. Chapter 3 Decision Structures and Boolean Logic 57 For the examples below: x = 5, y = 8, z = 5 x>y
5>8
False
5 is not greater than 8
x= 5
True
5 is equivalent to 5
x