Java – Defining a Thread by Implementing Runnable Interface | Code Factory

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              Runnable                           Runnable    
                 ↑                                  ↑      
              Thread                           MyRunnable              
                 ↑                                        
              MyThread                                           

• Runnable interface present in java.lang package and it contain only one method run()

package com.example.thread;

public class ThreadTest {
	public static void main(String... args) {
		MyRunnable r = new MyRunnable(); // Thread instantiation
		Thread t = new Thread(r); // r = target Runnable
		t.start(); // starting a Thread
		// executed by Main Thread (line no. 9 to 11)
		for(int i=0; i<5; i++) {
			System.out.println("Main Thread");
		}
	}
}

// Define a Thread (line no. 16 to 23)
class MyRunnable implements Runnable {
	public void run() {
		// job of Thread, executed by Child Thread (line no. 19 to 21)
		for(int i=0; i<5; i++) {
			System.out.println("Child Thread");
		}
	}
}

Output :

Main Thread
Main Thread
Main Thread
Main Thread
Main Thread
Child Thread
Child Thread
Child Thread
Child Thread
Child Thread

. . . . .

Case Study :

MyRunnable r = new MyRunnable();
Thread t1 = new Thread();
Thread t2 = new Thread(r);

Case 1 : t1.start()

• A new thread will be created which is responsible for the execution of Thread class run() method which has empty implementation

Case 2 : t1.run()

• No new thread will be created and Thread class run() method will be executed just like a normal method call

Case 3 : t2.start()

• A new thread will be created which is responsible for the execution of MyRunnable class run method

Case 4 : t2.run()

• A new thread wouldn’t be created and MyRunnable run() method will be executed just like a normal method call

Case 5 : r.start()

• We will get compile time error saying MyRunnable class doesn’t have start capability
• CE : cannot find symbol
• symbol : method start()
• location : MyRunnable

Case 6 : r.run()

• No new thread will be created and MyRunnable run() method will be executed like normal method call

. . . . .

• Among 2 ways of defining a Thread implement runnable approach is recommended.
• In the 1st approach our class always extends Thread class, there is no chance of extending any other class. Hence we are missing inheritance benefits.
• But in the 2nd approach while implementing runnable interface we can extend any other class. Hence we wouldn’t missing any inheriance benefit.
• Because of above reason implementing Runnable interface approach is recommended than extending Thread class.

. . . . .

Thread Class Constructors :

1. Thread t = new Thread();
2. Thread t = new Thread(Runnable r);
3. Thread t = new Thread(String name);
4. Thread t = new Thread(Runnable r, String name);
5. Thread t = new Thread(ThreadGroup g, String name);
6. Thread t = new Thread(ThreadGroup g, Runnable r);
7. Thread t = new Thread(ThreadGroup g, Runnable r, String name);
8. Thread t = new Thread(ThreadGroup g, Runnable r, String name, long stacksize);