Java - Thread Priority

Priority of a Thread in Java

Every Java thread has a priority that helps the operating system determine the order in which threads are scheduled. You can get and set the priority of a Thread. Thread class provides methods and constants for working with the priorities of a Thread.

Threads with higher priority are more important to a program and should be allocated processor time before lower-priority threads. However, thread priorities cannot guarantee the order in which threads execute and are very much platform dependent.

Built-in Property Constants of Thread Class

Java thread priorities are in the range between MIN_PRIORITY (a constant of 1) and MAX_PRIORITY (a constant of 10). By default, every thread is given priority NORM_PRIORITY (a constant of 5).

• MIN_PRIORITY: Specifies the minimum priority that a thread can have.

• NORM_PRIORITY: Specifies the default priority that a thread is assigned.

• MAX_PRIORITY: Specifies the maximum priority that a thread can have.

Thread Priority Setter and Getter Methods

• Thread.getPriority() Method: This method is used to get the priority of a thread.

• Thread.setPriority() Method: This method is used to set the priority of a thread, it accepts the priority value and updates an existing priority with the given priority.

Example of Thread Priority in Java

In this example, we're showing a simple one thread program where we're not declaring any thread and checking the thread name and priority in the program execution.

 package com.tutorialspoint; public class TestThread { public void printName() { System.out.println("Thread Name: " + Thread.currentThread().getName()); System.out.println("Thread Priority: " +Thread.currentThread().getPriority()); } public static void main(String args[]) { TestThread thread = new TestThread(); thread.printName(); } } 

Output

 Thread Name: main Thread Priority: 5 

More Examples of Thread Priority

Example 1

In this example, we've created a ThreadDemo class which extends Thread class. We've created three threads. Each thread is assigned a priority. In run() method, we're printing the priorities and in output, it is reflecting in threads execution.

 package com.tutorialspoint; class ThreadDemo extends Thread { ThreadDemo( ) { } public void run() { System.out.println("Thread Name: " + Thread.currentThread().getName() + ", Thread Priority: " +Thread.currentThread().getPriority()); for(int i = 4; i > 0; i--) { System.out.println("Thread: " + Thread.currentThread().getName() + ", " + i); } try { Thread.sleep(50); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public void start () { super.start(); } } public class TestThread { public static void main(String args[]) { ThreadDemo thread1 = new ThreadDemo(); ThreadDemo thread2 = new ThreadDemo(); ThreadDemo thread3 = new ThreadDemo(); thread1.setPriority(Thread.MAX_PRIORITY); thread2.setPriority(Thread.MIN_PRIORITY); thread3.setPriority(Thread.NORM_PRIORITY); thread1.start(); thread2.start(); thread3.start(); } } 

Output

 Thread Name: Thread-2, Thread Priority: 5 Thread Name: Thread-1, Thread Priority: 1 Thread Name: Thread-0, Thread Priority: 10 Thread: Thread-1, 4 Thread: Thread-2, 4 Thread: Thread-1, 3 Thread: Thread-0, 4 Thread: Thread-1, 2 Thread: Thread-2, 3 Thread: Thread-0, 3 Thread: Thread-0, 2 Thread: Thread-0, 1 Thread: Thread-2, 2 Thread: Thread-2, 1 Thread: Thread-1, 1 

Example 2

In this example, we've created a ThreadDemo class which extends Thread class. We've created three threads. As we're not setting any priority, each thread has a normal priority. In run() method, we're printing the priorities and in output, threads are executing in any order.

 package com.tutorialspoint; class ThreadDemo extends Thread { ThreadDemo( ) { } public void run() { System.out.println("Thread Name: " + Thread.currentThread().getName() + ", Thread Priority: " +Thread.currentThread().getPriority()); for(int i = 4; i > 0; i--) { System.out.println("Thread: " + Thread.currentThread().getName() + ", " + i); } try { Thread.sleep(50); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public void start () { super.start(); } } public class TestThread { public static void main(String args[]) { ThreadDemo thread1 = new ThreadDemo(); ThreadDemo thread2 = new ThreadDemo(); ThreadDemo thread3 = new ThreadDemo(); thread1.start(); thread2.start(); thread3.start(); } } 

Output

 Thread Name: Thread-1, Thread Priority: 5 Thread Name: Thread-2, Thread Priority: 5 Thread Name: Thread-0, Thread Priority: 5 Thread: Thread-2, 4 Thread: Thread-1, 4 Thread: Thread-1, 3 Thread: Thread-2, 3 Thread: Thread-0, 4 Thread: Thread-2, 2 Thread: Thread-1, 2 Thread: Thread-2, 1 Thread: Thread-0, 3 Thread: Thread-1, 1 Thread: Thread-0, 2 Thread: Thread-0, 1