java multi-threading thread demo

Multi threading is to spin up multiple threads to do stuff concurrently, each tread contains one running task. In java, there is a Thread class you can extend from and override its run method to do your custom task. The example below demonstrates the basic usage of extending the Tread class.
[code language=”java”]
public class ThreadDemo{
public static class Counter extends Thread {
private int SIZE;
private int counter = 0;
private String name;
public Counter(int size, String name) {
this.SIZE = size;
this.name = name;
}
@Override
public void run() {
while(this.counter < SIZE) {
this.counter++;
}
System.out.println("done counting," + this.name + "=" + this.counter);
}
}

public static void main(String args[]) {
int size = 1000000;
Counter counterA = new Counter(size, "CounterA");
Counter counterB = new Counter(size, "CounterB");
new Thread(counterA).start();
new Thread(counterB).start();
}
}
[/code]

Outout.Notice the CounterB finishes first even though it was started later. It’s becuase A and B are running concurrently, in this case, it just happens that B finished first. When you run the program again, A might finishes first, or it could be B finishes first again.
[code language=”text”]
done counting,CounterB=1000000
done counting,CounterA=1000000
[/code]