Threads - The Runnable Interface

• the Runnable interface declares a single method: run()
• you can execute a Runnable object in its own thread by passing it to a Thread constructor
• here's the BasicThread class modified to use the Runnable interface

class RunBasicThread implements Runnable{ 
char c;

RunBasicThread(char c) {
    this.c = c;
}    

// override run() method in interface
public void run() {
    for(int i=0; i<100; i++) {
        System.out.print(c);
        
        try{ 
           Thread.sleep((int)(Math.random() * 10));
        } catch( InterruptedException e ) {
            System.out.println("Interrupted Exception caught");
        }
    }
}    

public static void main(String[] args) {

    RunBasicThread bt = new RunBasicThread('!');
    RunBasicThread bt1 = new RunBasicThread('*');                

    // start RunBasicThread objects as threads
    new Thread(bt).start();    
    new Thread(bt1).start();
}
}

• the most significant code revisions are shown in red
• note that you can still make use of the methods declared in the Thread class but you now have to use a qualified name ie Thread.sleep() and you have to pass your runnable object to the thread when it is created ie new Thread(bt).start()

When to implement Runnable vs subclassing Thread

• Whenever your class has to extend another class, use Runnable. This is particularly true when using Applets

Example Code

• Click Applet
• Bouncing Ball applet: UpDown_1
• PrimeNumbers applet: Ex1_a
• Java Is Hot: Thread2