Previously we have discussed about
Daemon Thread
When we create a Thread in java, by default its a user defined thread.In order to create a daemon thread ,thread class provide a method named as setDaemon() which is used to set Thread as Daemon thread.
Daemon thread is a low priority based thread that runs in background to perform some tasks such as : garbage collection etc.
Daemon thread life depends upon on the user defined threads.
Thread.setDaemon(true) : This method makes a User Thread to Daemon thread but it can only be called before starting a Thread in java.It will throw IllegalThreadStateException if corresponding Thread is already started and running.
Thread.setDaemon(false) : This method makes Daemon Thread back to normal thread .
public boolean isDaemon() : This method is used to determine weather a thread is Daemon or not.
Difference between Daemon and Non Daemon Thread :
- JVM does not wait for any daemon thread to finish before exiting.
- Daemon threads are treated differently than user defined thread when JVM terminates, finally blocks are not called ,and JVM just exits.
Example of Daemon Thread:
public class DeamonThreadExample extends Thread {
public void run(){
try {
if(Thread.currentThread().isDaemon()){
System.out.println("Daemon Thread Executing.");
}
else{
System.out.println("Normal Thread is Executing.");
}
} catch (Exception e) {
e.printStackTrace();
} finally {
System.out.println("Daemon Thread Exiting.");
}
}
public static void main(String[] args) {
DeamonThreadExample t1 = new DeamonThreadExample();
DeamonThreadExample t2 = new DeamonThreadExample();
t1.setDaemon(true);
t1.start();
t2.start();
}
}
Program Output:
Daemon Thread Executing.
Normal Thread is Executing.
Daemon Thread Exiting.
Daemon Thread Exiting.
Example of Daemon Thread throwing Exception:
public class DeamonThreadExample extends Thread {
public void run(){
try {
if(Thread.currentThread().isDaemon()){
System.out.println("Daemon Thread Executing.");
}
else{
System.out.println("Normal Thread is Executing.");
}
} catch (Exception e) {
e.printStackTrace();
} finally {
System.out.println("Daemon Thread Exiting.");
}
}
public static void main(String[] args) {
DeamonThreadExample t1 = new DeamonThreadExample();
DeamonThreadExample t2 = new DeamonThreadExample();
t1.setDaemon(true);
t1.start();
t2.start();
}
}
Program Output:
Normal Thread is Executing.Exception in thread "main"
Daemon Thread Exiting.
java.lang.IllegalThreadStateException
at java.lang.Thread.setDaemon(Unknown Source)
at thread.DeamonThreadExample.main(DeamonThreadExample.java:23)
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