Daemon Thread in Java

Daemon thread in Java is a service provider thread that provides services to the user thread. Its life depend on the mercy of user threads i.e. when all the user threads dies, JVM terminates this thread automatically.

There are many java daemon threads running automatically e.g. gc, finalizer etc.

You can see all the detail by typing the jconsole in the command prompt. The jconsole tool provides information about the loaded classes, memory usage, running threads etc.

Points to remember for Daemon Thread in Java

It provides services to user threads for background supporting tasks. It has no role in life than to serve user threads.
Its life depends on user threads.
It is a low priority thread.

Why JVM terminates the daemon thread if there is no user thread?

The sole purpose of the daemon thread is that it provides services to user thread for background supporting task. If there is no user thread, why should JVM keep running this thread. That is why JVM terminates the daemon thread if there is no user thread.

Methods for Java Daemon thread by Thread class

The java.lang.Thread class provides two methods for java daemon thread.

No.	Method	Description
1)	public void setDaemon(boolean status)	is used to mark the current thread as daemon thread or user thread.
2)	public boolean isDaemon()	is used to check that current is daemon.

Simple example of Daemon thread in java

File: MyThread.java

public class TestDaemonThread1 extends Thread{
 public void run(){
  if(Thread.currentThread().isDaemon()){//checking for daemon thread
   System.out.println("daemon thread work");
  }
  else{
  System.out.println("user thread work");
 }
 }
 public static void main(String[] args){
  TestDaemonThread1 t1=new TestDaemonThread1();//creating thread
  TestDaemonThread1 t2=new TestDaemonThread1();
  TestDaemonThread1 t3=new TestDaemonThread1();

  t1.setDaemon(true);//now t1 is daemon thread
  
  t1.start();//starting threads
  t2.start();
  t3.start();
 }
}

Test it Now

Output:

daemon thread work
user thread work
user thread work

Note: If you want to make a user thread as Daemon, it must not be started otherwise it will throw IllegalThreadStateException.

File: MyThread.java

class TestDaemonThread2 extends Thread{
 public void run(){
  System.out.println("Name: "+Thread.currentThread().getName());
  System.out.println("Daemon: "+Thread.currentThread().isDaemon());
 }

 public static void main(String[] args){
  TestDaemonThread2 t1=new TestDaemonThread2();
  TestDaemonThread2 t2=new TestDaemonThread2();
  t1.start();
  t1.setDaemon(true);//will throw exception here
  t2.start();
 }
}

Test it Now

Output:

exception in thread main: java.lang.IllegalThreadStateException

Next TopicJava Thread Pool

← prev next →

Latest Courses

We provides tutorials and interview questions of all technology like java tutorial, android, java frameworks

Contact info

G-13, 2nd Floor, Sec-3, Noida, UP, 201301, India

[email protected].

Python

AI, ML and Data Science

Java

B.Tech and MCA

Web Technology

Software Testing

Technical Interview

Java Interview

Web Interview

Database Interview

Company Interviews

Java Tutorial

Control Statements

Java Object Class

Java Inheritance

Java Polymorphism

Java Abstraction

Java Encapsulation

Java Array

Java OOPs Misc

Java String

Java String Methods

Java Regex

Exception Handling

Java Inner Class

Java Multithreading

Java Synchronization

Java Networking

Java Applet

Java Reflection

Java Conversion

Java JDBC

RMI

Internationalization

Java Array Class

Java AtomicInteger Class

Java AtomicLong Methods

Java Authenticator

Java BigDecimal class

Big Integer Class

Java Boolean class

Java Byte Class

Java Class

Java Collections class

Java Compiler Class

CopyOnWriteArrayList

Java Math Methods

LinkedBlockingDeque

Java Long class

LinkedTransferQueue

Java List

Java MulticastSocket

Java Number Class

Java Phaser Class

ArrayList Methods

Java Thread Methods

Java Projects

Java Programs

Java Misc

Java Date Class

Java ListIterator Class

Java NIO Tutorial

HttpURLConnection

Java Deque

Java HttpCookie Class

Java URL class

Java List Methods

Java Vector class

Java Collection Methods

Java Socket Class

Java Executors