ISQS6337 JAVA

Jaeki Song

Lecture 03Introduction to Java

-The First Java Application-

ISQS6337 JAVA

Jaeki Song

Outline

• Object Oriented Programming

• Class

• Object

• Important Concepts

• Java Application

ISQS6337 JAVA

Jaeki Song

What is Java?

• Designed in the early of 1990s by Sun Microsystems

• Provide animation and interactivity on the World Wide Web– Web browsers have provided the

opportunities to run Java applets

• The fastest growing language

ISQS6337 JAVA

Jaeki Song

Java Language

• Standard language used for programming, creating applets, servlets, JavaBeans, and enterprise components

• Java is simple

• Java is object-oriented language

• Java is distributed

ISQS6337 JAVA

Jaeki Song

Java Language

• Java is interpreted– Need an interpreter to

run Java program– The program are

compiled into Java Virtual Machine (JVM) code called bytecode

Java Source Code

Java compiler

Java Bytecode Code

Java Interpreter

CPU

JVM

ISQS6337 JAVA

Jaeki Song

Java Language

• Java is robust– Reliabile

• Detect many problems

• Java is secure• Java is platform-independent• Java is portable

– Can be run on any platform without being recompiled

• Java is multithreaded

ISQS6337 JAVA

Jaeki Song

Java Virtual Machine (JVM)

• Interpreter for the Java programming language– a simple platform that all Java applications

run on.

• Comes with Java Development Kit (JDK)– Contains JVM and run-time system– Java 2 SDK

• www.sun.com

ISQS6337 JAVA

Jaeki Song

Java Environment

• Editor– Integrated Development Environment (IDE)

• Jbuilder, J++, Forte, Visual Cafe

• Compiler– Translate into bytecode

• For Sun Microsystems- javac (included in SDK)• Class loader produces .class file

• Loading– Applications

• loaded and executed using Java Interpreter java example.class

– Applet• loaded in the browser and could be viewed by applet viewer using the html

file in which the applet is placed.

ISQS6337 JAVA

Jaeki Song

Creating First Application

• The Java 2 Platform, Standard Edition

• JBuilder4 or 5

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Jaeki Song

JBuilder: Interface

Main menuProjecttoolbar

Projectpane

Structurepane

ContentpaneFile tab

File view tab

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Jaeki Song

Example

/* Assignment 1 Printing on the screen Programmer: Jaeki Song Student ID : 999-99-9999 Date : September 2001 Program Name: Address */

public class Address{

public static void main(String[] args) //method header{ System.out.println(“ Jaeki Song”); System.out.println(“ 1234 89th Street”);

System.out.println(“ Lubbock, TX, 79413”); }

}

ISQS6337 JAVA

Jaeki Song

Documentation

• Comments– Block comment

/* ….. */

– Line comment: //– e.g.

/* Assignment 1 Printing on the screen Programmer: Jaeki Song Student ID : 999-99-9999

Date : September 2001 Program Name: Address */

ISQS6337 JAVA

Jaeki Song

Java Class

• Java program consists of pieces called classes– Existing classes in Java Class Libraries

• Known as Java APIs (Applications Programming Interfaces)

• Classes consists of pieces called methods– Perform tasks and return information

ISQS6337 JAVA

Jaeki Song

Java Class

• A single class resides in a single Java source file with extension .java

• public class Address { …. }• The source code is Address.java.

– The name of the class is the name of the file

• Class name and file name must match

ISQS6337 JAVA

Jaeki Song

Main Method

• The class which contains the main() method is the class that starts running the program

• Every Java application (not applet) has a main class

public class Address{ public static void main(String[] args) { … }}

ISQS6337 JAVA

Jaeki Song

Access Modifier

• Specifies the circumstances in which the class can be accessed– E.g.: public class Address

{

…….

}

• Public indicates that this code can be access by all objects and can be extended or used as a basis for another class

• The contents of the class must be enclosed in braces { }

ISQS6337 JAVA

Jaeki Song

Methods and Method Header

public static void main(String[] args) //method header{

……

}

The methodas accessible to all classes

This method is for class

Three parts• return value

• method name

• arguments lists

Void means that this methoddoes not return a value when it is called

Method name is main. Mainmethod is the usual starting point for all stand-alone Java program

Piece of data. args is an identifier for any string or character argument

ISQS6337 JAVA

Jaeki Song

Body Code

{ System.out.println(“ Jaeki Song”); System.out.println(“ 1234 89th Street”); System.out.println(“ Lubbock, TX, 79413”); }

Out is the object that represents the default display

System is the name of the class (program-defined class)

Println is the name of a method thattakes a string argument. It returns its value to theSystem.out device

ISQS6337 JAVA

Jaeki Song

Using Java Swing Class

• Refers to the new library of GUI– A component set that makes up all the objects of GUI

• Displays output using windows or dialog boxes– Input Dialog and Output Dialog

• Use packages– Predefined classes grouped into categories of related

classes called packages (sometimes called java class libraries or java applications programming interface (API))

– JOptionPane• Defined in a package called javax.swing

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Jaeki Song

Output Dialog

• showMessageDialog ( null, “string”);– A method of class JOptionPane– Two arguments

• Syntax

JOptionPane.showMessageDialog(null, “string”);

ISQS6337 JAVA

Jaeki Song

Example: Output Dialog

import javax.swing.JOptionPane; //import class JOptionPane

public class Address{

public static void main(String[] args) //method header{ JOptionPane.showMessageDialog(

null, " Jaeki Song\n1234 89th Street\n Lubbock, TX, 79413"); System.exit(0); //terminate program }}

ISQS6337 JAVA

Jaeki Song

Output

ISQS6337 JAVA

Jaeki Song

Input Dialog

• Uses predefined dialog box from class JOptionPane called input dialog– Allows the user to input a value for use in the

program– Syntax

JOptionPane.showInputDialog(“ Enter first integer”);

ISQS6337 JAVA

Jaeki Song

Example: Add Integer

import javax.swing.JoptionPane;

public class AddInt{ public static void main (String args[]) {

String number1, number2; //first and second string entered by user int numInt1, numInt2, sum; number1 = JOptionPane.showInputDialog(“Enter first number”); number2 = JOptionPane.showInputDialog(“Enter second number”); numInt1 = Integer.parseInt(number1); numInt2 = Integer.parseInt(number2); sum = numInt1 + numInt2; JOptionPane.showMessageDialog(null, “The sum is “ + sum, “Results”,

JOptionPane.PLAIN_MESSAGE); System.exit(0); }}

ISQS6337 JAVA

Jaeki Song

Output