J ava P rogramming: From Problem Analysis to Program Design, From Problem Analysis to Program Design, D.S. Malik D.S. Malik

Java Programming: From Problem Analysis to Program Design, Second Edition 2 Chapter 1: An Overview of Computers and Programming Languages Chapter 1: An Overview of Computers and Programming Languages

Chapter 1: Overview  Components of a computer system  The language of a computer  Evolution of programming languages.  Processing a Java program  Problem-solving technique  Structured and object-oriented design methodologies Java Programming: From Problem Analysis to Program Design, Second Edition3

Introduction  Computers have greatly affected our daily lives—  helping us complete many tasks.  Computer programs (software) are designed specifically for each task.  Software is created with programming languages.  Java is an example of a programming language. Java Programming: From Problem Analysis to Program Design, Second Edition4

An Overview of the  History of Computers  1950s: Very large devices available to a select few.  1960s: Large corporations owned computers.  1970s: Computers got smaller and cheaper.  1990s: Computers got cheaper and faster and were found in most homes. Java Programming: From Problem Analysis to Program Design, Second Edition5

Elements of a Computer System  A computer has two components:  Hardware  Software Java Programming: From Problem Analysis to Program Design, Second Edition6

Hardware Components of a Computer  Central processing unit (CPU)  Main memory Java Programming: From Problem Analysis to Program Design, Second Edition7

Central Processing Unit  Control unit (CU)  Arithmetic logic unit (ALU)  Program counter (PC)  Instruction register (IR) Java Programming: From Problem Analysis to Program Design, Second Edition8

Main Memory  Ordered sequence of cells (memory cells).  Directly connected to CPU.  All programs must be brought into main memory before execution.  When power is turned off, everything in main memory is lost. Java Programming: From Problem Analysis to Program Design, Second Edition9

Secondary Storage  Provides permanent storage for information.  Examples of secondary storage:  Hard disks  Floppy disks  Zip disks  CD-ROMs  Tapes Java Programming: From Problem Analysis to Program Design, Second Edition10

Software  Software consists of programs written to perform specific tasks.  Two types of programs:  System programs  Application programs Java Programming: From Problem Analysis to Program Design, Second Edition11

System Programs  System programs control the computer.  The operating system (OS) is first to load when you turn on a computer.  The OS monitors the overall activity of the computer and provides services.  Example services provided by the OS:  Memory management  Input/output  Activities  Storage management Java Programing: From Problem Analysis to Program Design, Second Edition12

Application Programs  Written using programming languages.  Perform a specific task.  Run by the OS.  Example programs:  Word processors  Spreadsheets  Games Java Programming: From Problem Analysis to Program Design, Second Edition13

Language of a Computer  Machine language is the most basic language of a computer.  A sequence of 0s and 1s.  Every computer directly understands its own machine language.  A bit is a binary digit, 0 or 1.  A byte is a sequence of eight bits. Java Programming: From Problem Analysis to Program Design, Second Edition14

Language of a Computer Java Programming: From Problem Analysis to Program Design, Second Edition15

Evolution of Programming Languages  Early computers programmed in machine language.  Assembly languages were developed to make programmer’s job easier.  In assembly language, an instruction is an easy-to remember form called a mnemonic.  Assembler: Translates assembly language instructions into machine language. Java Programming: From Problem Analysis to Program Design, Second Edition16

Instructions in Assembly and Machine Languages Java Programming: From Problem Analysis to Program Design, Second Edition17

Java Programming: From Problem Analysis to Program Design, Second Edition18 Evolution of Programming Languages  High-level languages make programming easier.  Closer to spoken languages.  Examples:  Basic  FORTRAN  COBOL  C/C++  Java

Java Programming: From Problem Analysis to Program Design, Second Edition19 History Of Java  Developed by Sun Microsystems – a company known for its workstations.  Java is well known for developing internet applications. it is used to :  Create web pages with dynamic and interactive content.  Develop large –scale enterprise applications.  Enhance the functionality of WWW servers.  Provide applications for customer devices ( ex. Cell phones).  Java programs can run from a web browser.

Java Programming: From Problem Analysis to Program Design, Second Edition20 Basics of Java Environment  The environment  The language  Java applications programming Interface API  Various class libraries

Java Programming: From Problem Analysis to Program Design, Second Edition21 Processing a Java Program A Java program undergoes several stages : 1.Editing : use java code and save in a text file named className.java ( source program ). 2. Compiling : the compiler checks the source program for any syntax errors then translates the program into code understood by interpreter called bytecode saved in a file named className.class 3. Loading : the.class file is loaded into computer main memory for execution, and connected to all classes. 4. Verifying : to validate and secure against damage. 5. Interpreting : the Interpreter reads and translates each bytecode instruction into machine language and then executes it, one instrucion at a time.

Java Programming: From Problem Analysis to Program Design, Second Edition22 Processing a Java Program

 Compiler: A program that translates a program written in a high-level language into the equivalent machine language. (In the case of Java, this machine language is the bytecode.)  Source program: Written in a high-level language.  Loader: Transfers the compiled code (bytecode) into main memory.  Interpreter: Reads and translates each bytecode instruction into machine language and then executes it. Java Programming: From Problem Analysis to Program Design, Second Edition23

Java Programming: From Problem Analysis to Program Design, Second Edition24 Processing a Java Program  Java Virtual Machine (JVM): A hypothetical computer developed to make Java programs machine independent ( i.e run on many different types of computer platforms ).  Bytecode is the machine language for the JVM.

Java Programming: From Problem Analysis to Program Design, Second Edition25 Processing a Java Program Two types of Java programs:  applications : standalone programs stored and executed on a local computer.  applets : small programs stored on remote computers that users connect to via a WWW browser. Applets are loaded into the browser, executed then discarded.

Java Programming: From Problem Analysis to Program Design, Second Edition26 Example of a Java Program  A simple java application: an application executes using the java interpreter. Example : // This prints a line of text public class Welcome { public static void main (String args[] ) { System.out.println(“ welcome to java”) ; }

Java Programming: From Problem Analysis to Program Design, Second Edition27 Example of a Java Program  // single line comment  /* */ multiple line comment  Every java program must have at least one class.  Each class begins with a class declaration that defines data and methods for the class.  The class name here is Welcome, and contains a method main ()  Welcome is an identifier.

Java Programming: From Problem Analysis to Program Design, Second Edition28 Java Identifiers  Names of things. Such as methods, class names..  Consists of:  Letters  Digits  The underscore character ( _ )  The dollar sign ( $ )  Must begin with a letter, underscore, or the dollar sign. (i.e does not begin with a digit )  Java is case sensitive. A and a are different.

Java Programming: From Problem Analysis to Program Design, Second Edition29 Java Program- class definiton  Always begin a class name with a capital letter.  The class definition should be saved in a file that contains the class name.( i.e Welcome.java )  A file cannot contain two public classes.  public static void main (String args[]) is a part of every java application program.

Java Programming: From Problem Analysis to Program Design, Second Edition30 Java Program- class definiton  Java applications automatically begin executing at main ().  The parentheses () after main indicate that main is a method.  Class definitions normally contain one ore more methods.  One of those methods must be called main.  The void before main () means that main will not return any info.

Java Programming: From Problem Analysis to Program Design, Second Edition31 A Java Program public class ASimpleJavaProgram { public static void main(String[] args) { System.out.println("My first Java program."); System.out.println("The sum of 2 and 3 = " + 5); System.out.println("7 + 8 = " + (7 + 8)); } Class name Java o/p stmts Body of class Heading of method main

Java Programming: From Problem Analysis to Program Design, Second Edition32 A Java Program  A java output statement causes the program to evaluate whatever is in the parentheses and display the result on screen.  Anything in double quotation marks, called string, evaluates to itself.  + is used to concatenate the strings. The system automatically converts the number 5 into a string,joins that string with the first string,and displays it.

Java Programming: From Problem Analysis to Program Design, Second Edition33 A Java Program  The parentheses around 7+8 causes the system to add the numbers 7 and 8,resulting in 15.  The number 15 is then converted to string 15 and joined with string “7+8”= “. Sample Run: My first Java program. The sum of 2 and 3 = = 15

Java Programming: From Problem Analysis to Program Design, Second Edition34 A Java Program  The basic unit of a java program is a class.  Every class consists of one or more methods.  A method is a set of statements that accomplish something.  A java class must contain one main method if it is an application.  Execution always begins with method main in java application program.

Java Programming: From Problem Analysis to Program Design, Second Edition35 Internet,WWW and Java  Internet : is an interconnection of networks that allows computers around the world to communicate with each other.  In 197o’s, the US DOD developed techniques to interlink networks, i.e communication protocols so that networked computers could communicate  Internet  WWW uses s/w programs that enable users to view documents on any computer over the internet

Java Programming: From Problem Analysis to Program Design, Second Edition36 Internet,WWW and Java  The primary language of web is HTML, a simple language for laying out and linking documents.  HTML is not capable of interacting with users except to collect info via simple forms.  Java applets make the web responsive and interactive

Java Programming: From Problem Analysis to Program Design, Second Edition37 Programming Methodologies Two basic approaches to programming design:  Structured design  Object-oriented design

Java Programming: From Problem Analysis to Program Design, Second Edition38 Structured Design 1.A problem is divided into smaller sub-problems. 2.Each sub-problem is analyzed, solved and a solution for this sub-problem is obtained. 3.The solutions of all sub-problems are combined to solve the overall problem. 4.Is called structured programming, top-down design approach, or modular programming.

Java Programming: From Problem Analysis to Program Design, Second Edition39 Object-Oriented Design (OOD)  In OOD, a program is a collection of interacting objects.  An object consists of data and operations.  Steps in OOD: 1.Identify the objects which form the basis of the solution, then determine how these objects interact with each other. Example : write a program that automates the video rental process for a video store. The two main objects are : 1- video 2- customer

Java Programming: From Problem Analysis to Program Design, Second Edition40 Object-Oriented Design (OOD)  Steps in OOD: 2. Specify the relevant data for each object and the possible operations to be performed on that data. Example : for the video object o the data might be : movie name,Starring actors,and Number of copies in stock. oThe operations on video object might include : checking the name of the movie, reducing the # of copies in stock by 1 after renting a copy.

Java Programming: From Problem Analysis to Program Design, Second Edition41 Object-Oriented Design (OOD)  Each object consists of data and operations on those data  The final program is a collection of interacting objects.

Java Programming: From Problem Analysis to Program Design, Second Edition42 Problem-Analysis-Coding- Execution Cycle  Algorithm: A step-by-step, problem-solving process in which a solution is arrived at in a finite amount of time.

Java Programming: From Problem Analysis to Program Design, Second Edition43 Problem-Solving Process 1.Analyze the problem: Outline solution requirements and design an algorithm. 2.Implement the algorithm in a programming language (Java) and verify that the algorithm works. 3.Maintain the program: Use and modify if the problem domain changes.

Java Programming: From Problem Analysis to Program Design, Second Edition44 Problem-Analysis-Coding-Execution Cycle

example1  Design an algorithm to find the perimeter and area of a rectangle. Java Programming: From Problem Analysis to Program Design, Second Edition45

algorithm 1. get the length of the rectangle. 2. get the width of the rectangle. 3. Find the perimeter using the equation: perimeter = 2*(length + width) 4. Find the area using the equation: area = length* width Java Programming: From Problem Analysis to Program Design, Second Edition46

Example 2  Design an algorithm that calculates the average of 3 numbers. Java Programming: From Problem Analysis to Program Design, Second Edition47

algorithm 1. Get the three numbers A, B, C 2. Calculate the average average = (A+B+C) /3 3. print the average Java Programming: From Problem Analysis to Program Design, Second Edition48