Introduction to JAVA threads part 1

Simple java thread example retrieved from IBM developerWorks

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public class TwoThreads {
public static class Thread1 extends Thread {
public void run() {
System.out.println("A");
System.out.println("B");
}
}

public static class Thread2 extends Thread {
public void run() {
System.out.println("1");
System.out.println("2");
}
}

public static void main(String[] args) {
new Thread1().start();
new Thread2().start();
}
}

We have no idea in what order the lines will execute, except that “1″ will be printed before “2″ and “A” before “B.” The output could be any one of the following:

1 2 A B
1 A 2 B
1 A B 2
A 1 2 B
A 1 B 2
A B 1 2

Not only may the results vary from machine to machine, but running the same program multiple times on the same machine may produce different results. Never assume one thread will do something before another thread does, unless you’ve used synchronization to force a specific ordering of execution.

to be continued….