Daemon Threads

In this article we will learn what are daemon threads? and how to make thread as daemon thread along with example Java program.

 

A daemon thread is a thread which runs in the background. Example for daemon thread in Java is the garbage collector. In Java, thread can be divided into two categories:

1. User threads
2. Daemon threads

 

A user thread is a general thread which is created by the user. A daemon thread is also a user thread which is made as a daemon thread (background thread).

 

Difference between a user thread and a daemon thread is, a Java program will not terminate if there is at least one user thread in execution. But, a Java program can terminate if there are one or more daemon threads in execution.

 

To work with daemon threads, Java provides two methods:

 

void setDaemon(boolean flag)

boolean isDaemon()

 

The setDaemon() method is used to convert a user thread into a daemon thread. The isDaemon() thread can be used to know whether a thread is a daemon thread or not.

Below program demonstrates a daemon thread:

class ChildThread implements Runnable
{
	Thread t;
	ChildThread(String name)
	{
		t = new Thread(this, name);
		t.setDaemon(true);
		t.start();
	}
	public void run()
	{
		try
		{
			while(true)
			{
				System.out.println("This thread is a daemon thread: "+t.isDaemon());
				System.out.println(t.getName()+": Hi");
				Thread.sleep(1000);
			}
		}
		catch(InterruptedException e)
		{
			System.out.println("Child thread is interrupted");
		}
	}
}
class DaemonThread
{
	public static void main(String args[])
	{
		ChildThread one = new ChildThread("Daemon Thread");
	}
}

Java

 

Output of the above program is:

This thread is a daemon thread: true

Daemon Thread: Hi

Daemon Thread: Hi

Daemon Thread: Hi

Daemon Thread: Hi

…

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