Creating Multiple Threads

Creating Multiple Threads

So far, you have been using only two threads: the main thread and one child thread. However, your program can spawn as many threads as it needs.

 

For example, the following program creates three child threads:

 

// Create multiple threads.

class NewThread implements Runnable {

String name; // name of thread

Thread t;

NewThread(String threadname) {

name = threadname;

t = new Thread(this, name);

System.out.println("New thread: " + t);

t.start(); // Start the thread

}

// This is the entry point for thread.

public void run() {

try {

for(int i = 5; i > 0; i--) {

System.out.println(name + ": " + i);

Thread.sleep(1000);

}

} catch (InterruptedException e) {

System.out.println(name + "Interrupted");

}

System.out.println(name + " exiting.");

}

}

class MultiThreadDemo {

public static void main(String args[]) {

new NewThread("One"); // start threads

new NewThread("Two");

new NewThread("Three");

try {

// wait for other threads to end

Thread.sleep(10000);

} catch (InterruptedException e) {

System.out.println("Main thread Interrupted");

}

System.out.println("Main thread exiting.");

}

}

 

The output from this program is shown here:

New thread: Thread[One,5,main]

New thread: Thread[Two,5,main]

New thread: Thread[Three,5,main]

One: 5

Two: 5

Three: 5

One: 4

Two: 4

Three: 4

One: 3

Three: 3

Two: 3

One: 2

Three: 2

Two: 2

One: 1

Three: 1

Two: 1

One exiting.

Two exiting.

Three exiting.

Main thread exiting.

 

As you can see, once started, all three child threads share the CPU. Notice the call to sleep(10000) in main( ). This causes the main thread to sleep for ten seconds and ensures that it will finish last.