1 Chapter INTRODUCTION TO COMPUTERS AND JAVA
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COMPUTERS
A computer is a programmable electronic device that stores, retrieves, and processes a large quantity of data both quickly and accurately. A computer system consists of both hardware and software.
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COMPUTER HARDWARE
The physical components of the computer system are the hardware.
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COMPUTER HARDWARE The Central Processing Unit
The part of the computer that follows the instructions of a program is called the central processing unit (CPU). The CPU has two components, the control unit and the arithmetic logic unit. The control unit fetches the instructions of the executing program and sequences and controls the operations of other hardware components by sending them the appropriate signals. The arithmetic logic unit (ALU) performs arithmetic and logic operations including: addition, negation, multiplication, comparison, etc.
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COMPUTER HARDWARE The Central Processing Unit
When a computer program is executing the CPU performs a series of steps--the fetch/decode/execute cycle:
1. The control unit fetches the next coded instruction from memory. 2. The control unit translates the instruction into control signals. 3. The control signals are applied to tell the appropriate unit (ALU, memory, input device, output device, etc.) to perform some operation. 4. The sequence repeats from step 1 until the complete program is executed.
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COMPUTER HARDWARE Main Memory
The main memory of a computer is a device that stores both the instructions of executing programs and their data.
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COMPUTER HARDWARE Main Memory
A memory is an ordered sequence of storage locations or cells. Each cell has a distinct address, which is used in storing and retrieving information from the cell.
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COMPUTER HARDWARE Main Memory
The information in a computer is stored and manipulated in binary form, strings of 1's and 0's. A single 1 or 0 is called a binary digit or bit. A group of 8 bits is called a byte. Each addressable cell of the main memory is large enough to store an 8 bit (1 byte) code.
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COMPUTER HARDWARE Main Memory
The main memory is typically a type of memory known as random access memory (RAM). This is a volatile type of memory that can store information as long as the power is maintained. The information is lost if the computer is turned off or loses power. Programs and data that need to be saved long term are usually saved on some type of secondary storage device that is nonvolatile and are loaded into main memory to be used.
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COMPUTER HARDWARE
Secondary Storage
Secondary storage devices hold data and programs long term (even when the program is not running or the computer is turned off). These are loaded into main memory as they are needed. Typical secondary storage devices include:
hard drives floppy drives compact flash cards Read only CDs R/W CDs DVDs
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COMPUTER HARDWARE Input Devices
Input is data the computer gets from the outside world. We get data into the computer using some type of input device. Typical input devices include: keyboard mouse scanner digital camera
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COMPUTER HARDWARE Output Devices
Output is data the computer sends to the outside world. This data is sent using some type of output device. Typical output devices are: monitors printers speakers
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SOFTWARE
Computers can only do what they are programmed to do. A computer program is a set of instructions a computer follows to perform a task. The set of computer programs that run on a computer are called software.
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SOFTWARE
There are two general categories of software: Operating systems Application software
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SOFTWARE Operating Systems
An operating system has two functions: Manage and control the system resources Provide the user with a means of interaction with the computer Most operating systems today are multi-tasking. A multitasking operating system is capable of running multiple programs at once. (Windows, UNIX, Linux, and Mac OS X are multi-tasking operating systems).
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SOFTWARE
Application software
Application software includes the programs we use to do our jobs and to make our lives easier and more enjoyable. Commonly used types of application software word processors spreadsheets database systems email systems compilers photo editors video games
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PROGRAMMING LANGUAGES
A computer program is a set of instructions a computer follows to perform a task. These instructions form an algorithm for performing the task. An algorithm is a finite sequence of steps for solving a problem. (Think of an algorithm as an ordered list of steps for solving a problem).
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PROGRAMMING LANGUAGES Machine Language
In order to be understood by the computer, the algorithm must be written in the language of the computer processor. Each computer processor has its own distinct machine language. A machine language is a numeric language consisting of binary codes.
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PROGRAMMING LANGUAGES Machine Language
A machine language instruction might look something like the following:
1100000000100000000011000100
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PROGRAMMING LANGUAGES
The first computer programs were written in machine language. This was a very tedious and error prone process. To make the job of programming a computer easier, programmers eventually developed high-level programming languages, that use words instead of binary codes, and programs that can translate these languages to the underlying machine language of the computer processor.
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PROGRAMMING LANGUAGES High-Level Languages
Some commonly used high-level programming languages include: BASIC C C++ C# Perl Java
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PROGRAMMING LANGUAGES High-Level Languages
In this class we are going to learn Java, which is a popular high-level programming language that can be used to create large stand-alone application programs or small programs called applets that are used to enhance web pages.
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PROGRAMMING LANGUAGES Language Elements
There are certain elements that are common to high-level programming languages. These include: Key words Operators Punctuation Programmer defined identifiers Strict syntactic rules
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PROGRAMMING LANGUAGES Language Elements Key Words
Key words (reserved words) are special words reserved by the programming language to implement various features. These words cannot be used for anything other than their intended purpose. All Java key words contain only lowercase letters (Note: Java is case sensitive).
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PROGRAMMING LANGUAGES Language Elements Key Words
abstract assert boolean break byte case catch char class const continue default do double else enum extends false final finally float for goto if implements import instanceof int interface long native new null package private protected public return short static strictfp super switch synchronized this throw throws transient true try void volatile while
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PROGRAMMING LANGUAGES Language Elements Operators
Operators are symbols or words used to specify some manipulation of data. The symbols +, , *, /, and = are Java operators. See the inside cover of the text and Appendix C for additional Java operators.
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PROGRAMMING LANGUAGES Language Elements Punctuation
Punctuation includes symbols that delineate statements or separate items in a list. In Java, commas are used to separate items in a list. A semicolon marks the end of a Java statement.
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PROGRAMMING LANGUAGES Language Elements Statements vs. Lines
A statement is a complete instruction that causes the computer to perform some action. A statement may be spread over multiple lines of a program.
The following Java statement spans two lines:
System.out.println( "Hello students.\n");
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PROGRAMMING LANGUAGES Language Elements Programmer-Defined Identifiers
Programmer-defined identifiers are names created by the programmer for variables, methods, and other entities in programs. Variables are symbolic names for memory locations where data values may be stored.
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PROGRAMMING LANGUAGES Language Elements Syntax
Syntax is a set of rules that must be followed to construct programs in the language. Syntax rules include such things as how key words and operators may be used and where punctuation symbols are needed.
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// Source filename: RectangleArea.java // Written by: L. Thompson
Created using: jGRASP
// A program to calculate and display the area of a rectangle with side lengths entered by the user. import java.util.Scanner; public class RectangleArea { public static void main(String[ ] args) { double length, width; double area;
// The length and width of the rectangle // The area calculated for the rectangle
// Create a Scanner object to read input from the keyboard Scanner keyboard = new Scanner(System.in); // Get the dimensions of the rectangle from the user System.out.print("Enter the length of the rectangle: "); length = keyboard.nextDouble( ); System.out.print("Enter the width of the rectangle: "); width = keyboard.nextDouble( ); // Calculate the area of the rectangle area = length * width; // Display the results of the calculation System.out.print("\nA rectangle with length " + length + "\nand width "); System.out.println(width + " has an area of " area);
System.exit(0);
} + }
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THE COMPILER AND THE JAVA VIRTUAL MACHINE
When you write a Java program, you type it into a computer using a program called a text editor. The statements written by a programmer in a high-level programming language are called source code and they are saved in a file called a source file. Java source files have the .java extension.
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THE COMPILER AND THE JAVA VIRTUAL MACHINE
After your Java source code has been saved in the source file, you are ready to run the Java compiler. A compiler is a program that translates a program into an executable form. During the translation process, the compiler will find errors in the usage of the Java language, otherwise known as syntax errors. You will have to find these, correct them, and then resave and recompile your source code. When your program is free of syntax errors, the compiler will create another file that holds the translated instructions.
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THE COMPILER AND THE JAVA VIRTUAL MACHINE
Many programming languages like C and C++ are translated directly into files that contain machine language instructions. The Java compiler translates the source file into a file that contains byte code instructions. The byte code translation is stored in a file that has the .class extension. Byte code instructions are not in machine language, hence the CPU cannot directly execute them. The byte code is executed by the Java Virtual Machine.
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THE COMPILER AND THE JAVA VIRTUAL MACHINE
The Java Virtual Machine (JVM) is an interpreter (another program) that reads and executes the byte code instructions one after the other. The Java byte code is the same for all computers. This fact makes Java programs highly portable. By portable we mean that a program written and compiled on one type of computer processor can be executed/run on another type of computer. A compiled Java program can be run on any computer with a Java Virtual Machine. Each processor will have its own Java Virtual Machine.
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THE COMPILER AND THE JAVA VIRTUAL MACHINE
Note: Compilers only find syntax errors. Just because your program compiles that does not mean it is error free. Logical errors, errors in your design, may still be present.
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CREATING, COMPILING, AND RUNNING A JAVA PROGRAM USING jGRASP
jGRASP is an integrated development environment (IDE) that includes a text editor, compiler, debugger, and other utilities useful for creating programs.
*** See the document usingJGRASP.doc, which is available on webct.
Exercise: Find a small program in the text, like the one in Code Listing 1-1, create the source file and compile and run the program using jGRASP.
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THE PROGRAMMING PROCESS
The programming process includes: analysis, design, coding, testing, debugging, and maintenance activities.
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THE PROGRAMMING PROCESS Analysis
Analysis involves reviewing the program requirements and determining the purpose of the program, the data input to the program, the processing necessary, and the data/outputs that must be produced by the program. We want to ensure that we understand what we are being asked to do. We might sketch the computer screen(s) with sample input(s) and output(s) so we can visualize what the program user will see.
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THE PROGRAMMING PROCESS Analysis
For a simple program to calculate the area of a rectangle given the side lengths entered by the user at the keyboard, the following is probably sufficient: Purpose To calculate and display the area of a rectangle with side lengths entered by the user The length and width of the rectangle Multiply the length by the width of the rectangle to find the area of the rectangle Display an annotated message with the area of the rectangle
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Inputs Processing Output
PROGRAMMING PROCESS Analysis
Sample window for a program to calculate the area of a rectangle:
Enter the length of the rectangle: 4 Enter the width of the rectangle: 5 The area of the rectangle is: 20 square units
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THE PROGRAMMING PROCESS Design
After a thorough analysis of the problem you want to design a solution to the problem. We must decide how data is to be stored and develop algorithm(s) for calculations to be performed or processing to be done.
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THE PROGRAMMING PROCESS Design
Programmers often utilize modeling tools in the design process. You might use pseudocode, flow charts, UML diagrams during the design process.
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THE PROGRAMMING PROCESS Design Pseudocode
Pseudocode is a cross between human language and programming language that is often used by programmers to create an algorithm.
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THE PROGRAMMING PROCESS Design Pseudocode
Sample pseudocode for the program to calculate the area of a rectangle:
Ask the user to enter the length of the rectangle Store the value entered in length Ask the user to enter the width of the rectangle Store the value entered in width Multiply the length by the width and store the result in the area variable Display the area of the rectangle
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THE PROGRAMMING PROCESS Design Pseudocode
For this course, your pseudocode must be detailed enough that it names all the variables and describes all mathematical calculations either in words or formulas.
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THE PROGRAMMING PROCESS Design Test Plan
It is in the design phase of the programming process that the majority of the test plan development should be done. The development of a test plan involves the creation of many input combinations on which the completed program is to be tested along with the expected results for each input combination. Sample input that is likely to cause problems should be included. Try the maximum and minimum values in the expected input range. These are called boundary conditions. Values just outside the range of possible values should also be tested.
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Sample test plan for the program to calculate the area of a rectangle:
Inputs length = 3 width = 5 length = 10 width = 500 length = 9.75 width = 2 length = 0.3 width = 10.2 length = 0 width = 5 length = 4 width = 0 length = -1 width = 5.2 length = 5 width = -1.2 Expected Output Value
area =15
area = 5000
area = 19.5
area = 3.06
Error, length should not be 0
Error, width should not be 0
Error, length should not be negative
Error, width should not be negative
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THE PROGRAMMING PROCESS Design Test Plan
The algorithm/models should themselves be checked before proceeding to write code. You can do this by going through the model by hand, using a small number of the test cases.
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THE PROGRAMMING PROCESS Coding
Coding involves writing the program in the programming language and entering it in the source file.
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THE PROGRAMMING PROCESS Testing and Debugging
Testing a program means determining if it satisfies all the requirements of the specification and performs as expected. Testing involves running the test cases in the test plan, recording the actual output, and comparing the actual output with the expected output you projected when the test cases were designed. Programmers call errors in their programs bugs and the process of locating errors and correcting the errors debugging.
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THE PROGRAMMING PROCESS Testing and Debugging
If an error is found, you will have to go back to either the analysis or the design phase. From this point, you must go through all of the subsequent phases in order: redo your model, recode, retest, and debug.
************************************************* If you change your code in any way, you must retest your program on all the test cases, even those that previously produced correct output. *************************************************
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THE PROGRAMMING PROCESS Maintenance
Once the program is completed, it enters the maintenance phase. During the maintenance phase, the program is used for its intended purpose, errors found during use are corrected (don't forget to rerun all the test cases), and the program is sometimes modified to meet changing requirements.
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THE PROGRAMMING PROCESS SOFTWARE ENGINEERING
The job of developing computer programs involves so much more than just writing code/programming. The process of crafting software is called software engineering and the professionals that engage in the process are called software engineers.
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PROCEDURAL AND OBJECT-ORIENTED PROGRAMMING
Procedural and object-oriented programming are two methodologies used for developing software.
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PROCEDURAL AND OBJECT-ORIENTED PROGRAMMING
Procedural programming is action oriented. The programmer divides the statements of the program into procedures called methods that perform some specific task. Methods contain their own variables, but often they share variables with other procedures.
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PROCEDURAL AND OBJECT-ORIENTED PROGRAMMING
In object-oriented programming, the program is divided into entities called objects. An object has fields of data called attributes and a set of functions, called methods, which are the only means to manipulate the data in the object. Operations are carried out by sending an object a message requesting that it perform some operation (execute a method) on its attributes.
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PROCEDURAL AND OBJECT-ORIENTED PROGRAMMING
Java was designed for object-oriented programming, but supports both object-oriented and procedural programming.
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