Java Thread start() method

The start() method of thread class is used to begin the execution of thread. The result of this method is two threads that are running concurrently: the current thread (which returns from the call to the start method) and the other thread (which executes its run method).

The start() method internally calls the run() method of Runnable interface to execute the code specified in the run() method in a separate thread.

The start thread performs the following tasks:

It stats a new thread
The thread moves from New State to Runnable state.
When the thread gets a chance to execute, its target run() method will run.

Syntax

Return value

Exception

IllegalThreadStateException - This exception throws if the start() method is called more than one times.

Example 1: By Extending thread class

public class StartExp1 extends Thread
{  
    public void run()
    {  
        System.out.println("Thread is running...");  
    }  
    public static void main(String args[])
    {  
        StartExp1 t1=new StartExp1();  
        // this will call run() method
        t1.start();  
    }  
}  

Test it Now

Output:

Thread is running...

Example 2: By Implementing Runnable Interface

public class StartExp2  implements Runnable
{  
    public void run()
    {  
        System.out.println("Thread is running...");  
    }  
    public static void main(String args[])
    {  
        StartExp2  m1=new StartExp2 ();  
        Thread t1 =new Thread(m1);  
        // this will call run() method
        t1.start();  
    }  
}

Test it Now

Output:

Thread is running...

Example 3: When you call the start() method more than one time

public class StartExp3 extends Thread
{  
    public void run()
    {  
    System.out.println("First thread running...");  
    }  
    public static void main(String args[])
    {  
        StartExp3 t1=new StartExp3();  
        t1.start();  
        // It will through an exception because you are calling start() method more than one time 
        t1.start();  
    }  
}  

Test it Now

Output:

First thread running...
Exception in thread "main" java.lang.IllegalThreadStateException
	at java.lang.Thread.start(Thread.java:708)
	at StartExp3.main(StartExp3.java:12)

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