Java

1
Java
2
Java Characteristics

• Object-Oriented
• Distributed
• Platform Independent

3
Program Execution
Java Source Code
Java Compiler
Java byte-code
Byte-code interpreter
Byte-code compiler
Java chip
JVM
JVM
4
JVM

• Uses multiple 32-bit registers.
• program counter
• reference to operand stack
• reference to local variables
• reference to activation frames
• Garbage collected heap for storage of run-time
  objects.

5
Java Programs

• Applets
• Embedded in web pages, invoked when web page is
  loaded.
• Apps
• Application which can be run by the user on a
  given machine (requires JRE).

6
Applet Security

• Shielded Memory Addresses
• Verification of Byte-code
• Run-time security manager

7
Applet

• /
• Trivial applet that displays a string - 4/96 PNL
• /
• import java.awt.
• import java.applet.Applet
• public class TrivialApplet extends Applet
• public void init()
• repaint()
• public void paint( Graphics g )
• g.drawString( "Hello World!", 30, 30 )

8
App

• /
• Trivial application that displays a string -
  4/96 PNL
• /
• public class TrivialApplication
• public static void main(String args)
• System.out.println( "Hello World!" )