Java Thread Priority

In Java Multithreading, every thread has a priority. Priority is an integer in the range of 1 to 10, where 1 is the lowest priority and 10 is the highest priority. The default priority of a thread is 5 (Normal Priority).

The priority of a thread is assigned by the JVM or by the programmer itself, explicitly through the Java code. The thread priority is used by the thread scheduler to pick up the threads for execution based on the priority.

The thread scheduler first executes the highest priority threads and then the lowest priority threads, but it also depends on the JVM implementation. If there are multiple threads with different priorities, it uses preemptive scheduling based on priority. In a situation where multiple threads have the same priority, it may use the FCFS (First Come, First Server) concept or wait time.

As given below, the Java Thread class has provided two methods for getting and setting the thread priority.

public final int getPriority(): This method returns the priority of the given thread.

public final void setPriority(int newPriority): This method updates the priority of the thread to newPriority. If we set our of specified range of priority value then this method throws java.lang.IllegalArgumentException.

  public class ThreadPriorityExample extends Thread {
    public void run() {
      System.out.println("Inside the run() method");
    }
  
    public static void main(String[] args) {
      // Creating threads with the help of ThreadPriorityExample class
      ThreadPriorityExample t1 = new ThreadPriorityExample();
      ThreadPriorityExample t2 = new ThreadPriorityExample();
      ThreadPriorityExample t3 = new ThreadPriorityExample();
  
      // Using getPriority() method, Fetching the thread priority
      System.out.println("Thread default priority:");
      System.out.println("t1 Thread Priority : " + t1.getPriority());
      System.out.println("t2 Thread Priority : " + t2.getPriority());
      System.out.println("t3 Thread Priority : " + t3.getPriority());
  
      // Using setPriority() method, Setting different priorities
      // of threads by passing integer values
      t1.setPriority(3);
      t2.setPriority(5);
      t3.setPriority(8);
  
      System.out.println(); 			// New Line
      
      // After setting different thread priority, 
      // Now printing the updated thread priority
      System.out.println("Thread updated priority:");
      System.out.println("t1 Thread Priority : " + t1.getPriority());
      System.out.println("t2 Thread Priority : " + t2.getPriority());
      System.out.println("t3 Thread Priority : " + t3.getPriority());
  
      System.out.println(); 			// New Line
      
      // Main thread,
      // Displays the name of currently executing Thread
      System.out.println("Current Executing Thread : " + Thread.currentThread().getName());
      System.out.println("Main thread priority : " + Thread.currentThread().getPriority());
  
      // Setting highest priority (10) for Main thread
      Thread.currentThread().setPriority(10);
  
      System.out.println("Main thread priority : " + Thread.currentThread().getPriority());
    }
  }

Thread default priority:
t1 Thread Priority : 5
t2 Thread Priority : 5
t3 Thread Priority : 5

Thread updated priority:
t1 Thread Priority : 3
t2 Thread Priority : 5
t3 Thread Priority : 8

Currently Executing Thread : main
Main thread priority : 5
Main thread priority : 10

  public class ThreadPriorityExample2 extends Thread {
    public void run() {
      System.out.println("Thread " + Thread.currentThread().getName() + " started " + 
          "with Priority : " + Thread.currentThread().getPriority());
    }
    
    public static void main(String[] args) {
      
      // Creating threads with the help of ThreadPriorityExample class
      ThreadPriorityExample2 tread1 = new ThreadPriorityExample2();
      ThreadPriorityExample2 tread2 = new ThreadPriorityExample2();
      ThreadPriorityExample2 tread3 = new ThreadPriorityExample2();
      
      // Using Thread Constant setting Threads Priority
      tread1.setPriority(MIN_PRIORITY);
      tread2.setPriority(NORM_PRIORITY);
      tread3.setPriority(MAX_PRIORITY);
      
      // Start thread execution
      tread1.start();
      tread2.start();
      tread3.start();
    }
  }

Thread Thread-0 started with Priority : 1
Thread Thread-2 started with Priority : 10
Thread Thread-1 started with Priority : 5

Java Thread Priority

Thread Priority - Interview Questions and Answers

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