Java programming course: 12.3 Implementing the Runnable interface

In the previous lesson we showed how to extend the Thread class.

• Previous lesson: 12.2 Extending the Thread class
• Course contents

Implementing the Runnable interface

You have seen that you can extend the Thread class to define a class which can run concurrently with other threads, but what if the class you want to make multithreaded already extends some other class? The answer is to instead implement the Runnable interface.

Suppose you want Visitor[1] objects to be multithreaded, so you decide to create a new class VisitorBooker:

package virtualzoo.core;

import com.example.util.*;

public class VisitorBooker extends Visitor implements Runnable {
    
    private BookingCounter booking;
    
    public VisitorBooker(Person person, Email email,
						 BookingCounter courseing) {
        super(person, email);
        this.booking = booking;
    }

    @Override
    public void run() {
        booking.makeBooking();
    }
    
}
 

• The VisitorBooker class extends Visitor so it can't also extend Thread. Therefore, it has been declared as implementing the Runnable interface
• The Runnable interface has a run() method which you need to write code for, being the same as for the Booker class
• Note that the Visitor class needs a Person and Email object so these are obtained via the constructor

You only need a couple of minor changes in the Experiments class to use VisitorBooker instead of Booker:

// Create a single booking counter
BookingCounter booking = new BookingCounter();
      
// Create a Person and an Email
Person p = new Person("Fred");
Email e = new Email("");
        
// Create 100 VisitorBooker threads using same BookingCounter
for (int i = 0; i < 100; i++) {
    VisitorBooker vb = new VisitorBooker(p, e, courseing);
    Thread t = new Thread(vb);
    t.start();
}
        
// Allow time for all threads to complete
try {
    Thread.sleep(1000);
} catch (InterruptedException ex) {
    System.out.println(ex.getMessage());
}
System.out.println("Number of bookings  made: " + booking.getCount());
 

• You will need to import com.example.util
• A Person object and an Email object are created because they are required by the Visitor class
• One hundred VisitorBooker objects are created (each of which is Runnable)
• A Thread object is created, passing the Runnable to it (in this case, being each VistorBooker)
• The start() method is invoked on the Thread object

Essentially, implementing the Runnable interface resulted in one additional line of code to make use of it: instantiating a Thread object passing the Runnable object as its argument.

In the next lesson we will look at thread waiting and notification.

Next lesson: 12.4 Thread waiting and notification