Rule
http://www.janeg.ca/scjp/threads/overview.html
- on an operating system a running program is known as a process 
- a single process can have seperate runnable tasks called threads 
- a thread is a single sequential flow of control within a process 
- a thread is also referred to as a lightweight process 
- with a single-processor CPU, only one thread is executing at any given time 
- the CPU quickly switches between active threads giving the illusion that they are all executing at the same time (logical concurrency) 
- on multi-processor systems several threads are actually executing at the same time (physical concurrency) 
- multi-programming occurs when multiple programs or processes are executed 
- multi-threading occurs when concurrency exists amoung threads running in a single process (also referred to as multi-tasking) 
- Java provides support for multi-threading as a part of the language 
- support centers on the: 

- java.lang.Thread class 

- java.lang.Runnable interface 

- java.lang.Object methods wait(), notify(), and notifyAll 

- synchronized keyword 
- every Java program has at least one thread which is executed when main() is invoked 
- all user-level threads are explicitly constructed and started from the main thread or by a thread originally started from main() 
- when the last user thread completes any daemon threads are stopped and the application stops 
- a thread's default daemon status is the same as that of thread creating it 
- you can check the daemon status using isDaemon() 
- you can set the daemon status using setDaemon(). 

public class slownum1 {
public static void main(String a[]) { 
  int cnt = 0;
  while (true) {
    try {
      Thread.currentThread().sleep(1000);
      cnt++;
    } catch (InterruptedException e) { }
    System.out.println(cnt);
  }
} 
}

import java.io.*;
public class slownum2 {
  public static void main(String a[]) throws InterruptedException {
  int cnt = 0;
  while (true) {
    Thread.currentThread().sleep(1000);
    cnt++;
    System.out.println(cnt);
  }
} 
}

/* 
DOS>javac numrun.java
DOS>appletviewer numrun.java
<applet code="numrun.class" width=99 height=200></applet> 
*/
import java.awt.*;
import java.applet.*;
public class numrun extends Applet implements Runnable {
  Thread timer;
  int cnt;         
  public void paint(Graphics g) { 
    g.setColor(Color.white);
    g.drawString(Integer.toString(cnt),1,cnt); 
  }
  public void start() {
    setBackground(Color.black);
    timer = new Thread(this);
    timer.start();
  }
  public void run() {
    Thread me = Thread.currentThread();
    while (timer == me) {
      try {
        Thread.currentThread().sleep(100);
        cnt++;
      } catch (InterruptedException e) { }
      repaint();
    }
  } 
}