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					Java
Understanding the “Java”
environments
Java is more than a language
  Language is C-like
     Same control constructs
     Similar Syntax
     Things do what you think they would.
  Java “packages” allow you to manage
  related classes as a unit.
  JVM can run almost anywhere.
Java environments
  Applications
     Command Line
     Local GUI
  Applets- run in browser
  Servelets – run in server
  Java Server pages – servelets that start as
  java embedded into HTML.
  Security issues
Concept Review
  Java environments designed for the
  Web.
  Java works everywhere imaginable
  Only real competition is Microsoft .NET
  Similar Architectures.
Applications: CLI and GUI

     JVM directly      Application:
    on Desktop OS      Class file on
                       local Disk
     Desktop Machine
Applets: Java in the Browser

     JVM directly         Application
    on Desktop OS

     Desktop Machine                      Server

     Browser
                                           Web
                          Applet: Class   Server
     JVM Inside Browser   file on Web
                          Server
Java on the Server


                   JVM runs     Tomcat
                   Web Server
Desktop
Machine                Server

Browser
                 JVM    Web
                       Server   Nescape
          HTML
Java on the Server


                   8080
                      Tomcat JVM              Class file
                              Java Servelet   on Server
Desktop
Machine                   Server

Browser
                    PHP
                 Interpreter Apache

          HTML                80
Java on the Server



Desktop
Machine                   Server
                                            Class file
Browser                     Java Servelet   on Server
                 8080
                        Tomcat JVM

          HTML              80
Packages, Collections,
Containers, and Environments
  JAR
  Foundation classes
  JavaBeans
  Collections
  JINI
  IDL– ORBs
  JDBC
Applications and Applets
  Getting the Java environment to work.
     www.Java.sun.com
     Test Application
     Test Applet
     System Architecture
Getting the Java Environment
  Free to use
  Not bad tools
  Several IDE’s
  It took me about 4 hours to get things
  all sorted out and take the “Getting
  Started” tutorials.
Test Application: Hello World!
  HelloWorldApp.java
  Compile to bytecodes
  Execute on virtual machine
     Command line stuff is easier to
      understand.
     GUI is a bit more difficult
Command Line:
 public class HelloWorldApp {
       public static void main(String[] args) {
       System.out.println("Hello World!");
       }
 }
Compile, Run
 >javac HelloWorldApp.java
 >java HelloWorldApp
 Hello World!
 >
GUI Window:
 import java.awt.*;
 public class HelloGUI extends Frame {
  private static Font f;
Fonts and positioning
 private void drawCenteredString (Graphics g, String s){
    Dimension d = getSize();
    FontMetrics fm=getFontMetrics(f);
    int x=(d.width-fm.stringWidth(s))/2;
    int y=(d.height-((d.height-fm.getHeight())/2);
    g.drawString(s,x,y);
  }
Paint method:
 public void paint(Graphics g) {
   g.setFont(f);
   g.setColor(Color.red);
   drawCenteredString(g,”Hello in a window!”);
 }
Main program:
 public static void main(String[] args) {
     Frame theFrame = new HelloGUI();
     theFrame.setTitle (“Java Hello World!”);
     theFrame.setSize (250,100);
     f=new Font(“Helvetica”,Font.BOLD, 24);
     theFrame.show();
 }
Applet:
 import java.applet.Applet;
 import java.awt.Graphics;
 public class HelloAppet extends Applet {
     public void paint (Graphics theGraphics); {
      theGraphics.drawString(“Hello in Applet!”,0,50);
     }
 }
HTML to invoke Applet:
<HTML>
<BODY>
<APPLET CODE=“HelloApplet.class” WIDTH=“200”
HEIGHT=“200”>
</APPLET>
</BODY>
</HTML>
Tomcat Demo          http://localhost:8080



  Browser                   Desktop
                            Machine:
                            localhost


                                             X.jsp
                          JSP Compiler
                                             X.java
                          Java Compiler
              8080   Tomcat JVM              X.class


              HTML      Java Servelet

				
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posted:12/5/2011
language:English
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