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A multithreaded Java program contains multiple threads running concurrently within a program, where each thread is performing some specific task. In this article we are going to teach you how to run multiple threads in a Java program.

Unsynchronized run of multiple threads, each thread based on one object

We are going to create three threads based on an the same object of a class that has implemented Runnable interface. Method start() on each thread will be called one by one. Each thread will run only for a short while, before it is replaced by another thread, in the middle of its execution, this is called unsychronized run of multiple threads

//class A implementing Runnable interface
  
class A implements Runnable
{

public void run()
{
for(int i=0;i<3;i++)
System.out.println(Thread.currentThread().getName()); //accessing the reference to the currently										
}						      //executing thread by calling static method
						      //currentThread() of Thread class.
						      


public static void main(String... ar)
{
A ob= new A();

Thread t1= new Thread(ob,"Thread1");
Thread t2= new Thread(ob,"Thread2");
Thread t3= new Thread(ob,"Thread3");	    //Calling Thread's constructor & passing the object
					    //of A class that  implemented  Runnable interface
					    //& the name of new thread.

						
t1.start(); //Starting the first thread
t2.start(); //Starting the second thread
t3.start(); //Starting the third thread
}
}

Output is -

Thread1
Thread3
Thread3
Thread3
Thread1
Thread1
Thread2
Thread2
Thread2

Program Analysis

• We have created 3 threads based on the same object of A class. Each thread is given a different name.
• Method start() is called on each thread, which automatically calls its run() method to start its execution
• In run() method, each thread cycles through for-loop three times, printing its own name .
• As you may see the output, it has been a unsynchronized run of threads, as each thread was replaced by another thread in the middle of its execution of for-loop.

To see the synchronized run of this program, please read our next article.

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Unsynchronized run of multiple threads, each thread based on a different object.

In this program we are going to create three threads based on a different object of a class that has implemented Runnable interface. In the run() method, each thread goes to sleep for 1 second and at that time, it is replaced by another thread, which starts executing the run() method.

//class A implementing Runnable interface

class A implements Runnable
{

public void run()
{
for( int i=0;i<3;i++)
try
{
	Thread.sleep(1000);
	System.out.println(Thread.currentThread().getName());//accessing the reference to the 								
}						 //currently executing thread by calling 
}						 //static method currentThread() of Thread class.

catch(Exception e)
{
System.out.println(e);
}

}


public static void main(String... ar)
{
A ob1= new A();
A ob2= new A();
A ob3= new A();


Thread t1= new Thread(ob1,"ThreadA");
Thread t2= new Thread(ob2,"ThreadB");
Thread t3= new Thread(ob3,"ThreadC");	    //Calling Thread's constructor & passing the object
					    //of A class that  implemented  Runnable interface
					    //& the name of new thread.

t1.start(); //Starting the first thread
t2.start(); //Starting the second thread
t3.start(); //Starting the third thread

}
}

Output is -:

ThreadA
ThreadB
ThreadC
ThreadB
ThreadC
ThreadA
ThreadC
ThreadB
ThreadA

Program Analysis

• We have created three threads, with each thread based on a different object of A class.
• Method start() is called on each thread, which automatically calls its run() method to start its execution
• In run() method, each thread cycles in for-loop, three times. In each cycle, there is a delay of 1 second and the name of executing thread is printed.
• You may see in output, it has been an unsynchronized run of threads, as each thread was replaced by another thread in the middle of its execution of the run() method, when sleep() method was called on it.

To see the synchronized run of this program, please read the next article

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