jaeki song isqs6337 java lecture 03 introduction to java -the first java application-
TRANSCRIPT
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
ISQS6337 JAVA
Jaeki Song
JBuilder: Interface
Main menuProjecttoolbar
Projectpane
Structurepane
ContentpaneFile tab
File view tab
ISQS6337 JAVA
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
ISQS6337 JAVA
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