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Priority of a Thread in Java

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When using multithreading, the operating system’s scheduler assigns each thread a different level of urgency or significance before it is run. Threads with higher priority values get more CPU time than threads with lower priority values.

This prioritization can be used to control the order and frequency of thread execution, which is essential in systems with limited resources or real-time requirements. Every thread is given a priority. It should be noted that a Java programmer can explicitly assign a thread’s priority in a Java program in addition to the JVM.

Three constants are defined in the Thread class:

A thread has a priority of 5 by default (NORM_PRIORITY). MAX_PRIORITY is set to 10, while MIN_PRIORITY is set to 1.

how to get and set a thread’s priority in Java:

Setter & Getter Thread Priority Method in Java

Program:

Example 1:

import java.lang.*;  
public class TechVidvan extends Thread   
{  
public void run()  
{  
System.out.println("Inside the run() method");  
}  
public static void main(String argvs[])  
{  
TechVidvan tv1 = new TechVidvan();  
TechVidvan tv2 = new TechVidvan(); 
TechVidvan tv3 = new TechVidvan();  
System.out.println("Priority of the thread tv1 is : " + tv1.getPriority());  
System.out.println("Priority of the thread tv2 is : " + tv2.getPriority());  
System.out.println("Priority of the thread tv2 is : " + tv2.getPriority());  
tv1.setPriority(6);  
tv2.setPriority(3);  
tv3.setPriority(9);  
System.out.println("Priority of the thread tv1 is : " + tv1.getPriority());  
System.out.println("Priority of the thread tv2 is : " + tv2.getPriority());  
System.out.println("Priority of the thread tv3 is : " + tv3.getPriority());  
System.out.println("Currently Executing The Thread : " + Thread.currentThread().getName());  
System.out.println("Priority of the main thread is : " + Thread.currentThread().getPriority());  
Thread.currentThread().setPriority(10);   
System.out.println("Priority of the main thread is : " + Thread.currentThread().getPriority());  
}
}

Output:

Priority of the thread tv1 is: 5
Priority of the thread tv2 is: 5
Priority of the thread tv2 is: 5
Priority of the thread tv1 is: 6
Priority of the thread tv2 is : 3
Priority of the thread tv3 is: 9
Currently Executing The Thread: main
priority of the main thread is: 5

Explanation:

We are aware that when it comes to thread execution, a thread with a high priority will take precedence over threads with a lower priority. Two threads may, however, share the same priority under other circumstances.

The Java thread scheduler does all of the work required to manage the threads. To understand what will happen if two threads have the same priority, consider the scenario that follows.

Example 2:

import java.lang.*;  
public class TechVidvan extends Thread   
{  
public void run()  
{  
System.out.println("Inside the run() method");  
}  
public static void main(String argvs[])  
{  
Thread.currentThread().setPriority(7);  
System.out.println("Priority of the main thread is : " + Thread.currentThread().getPriority());  
TechVidvan tv1 = new TechVidvan();  
System.out.println("Priority of the thread tv1 is : " + tv1.getPriority());  
}  
}

Output:

Priority of the main thread is: 7
Priority of the thread tv1 is: 7

Explanation:

The algorithm used by the thread scheduler (such as First Come, First Serve, Round-Robin, etc.) will then determine how things are carried out.

IllArgumentException Example:

We are aware that the IllegalArgumentException is thrown if the value of the newPriority parameter of the getPriority() function is outside the range (1 to 10). Let’s use an illustration to observe this.

Program:

import java.lang.*;  
public class TechVidvan extends Thread   
{  
public static void main(String argvs[])  
{  
Thread.currentThread().setPriority(17);  
System.out.println("Priority of the main thread is : " + Thread.currentThread().getPriority());  
}  
}

Output:

Exception in thread “main” java.lang.IllegalArgumentException
at java.base/java.lang.Thread.setPriority(Thread.java:1136)at TechVidvan.main(IllegalArgumentException.java:7)

Issues:

Explanation:

Thread Execution

A scheduling method known as fixed-priority pre-emptive scheduling is supported by the JVM. Every Java thread has a priority, and the JVM gives the highest priority thread the most attention first.

A Thread inherits its default priority when it is created. The JVM chooses and executes the Runnable thread with the highest priority when several threads are prepared to run. The lower priority threads will run in the event that this thread is terminated or becomes unrunnable. The JVM will execute threads in FIFO order if they have the same priority.

There are two situations that may result in the execution of a separate thread:

Summary

Java Thread priority is crucial for managing the execution order and resource allocation in multi-threaded applications. Without explicit priority settings, threads may execute in an unpredictable manner. By assigning priority levels to threads, developers can influence the order and frequency of thread execution, which can be especially useful in scenarios where certain threads require immediate attention or real-time responsiveness. However, the actual behavior can vary based on the underlying operating system and scheduler implementation.

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