Java Thread Priorities: Types and Default Value Explained

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質問：

What are the different types of Thread Priorities in Java? And what is the default priority of a thread assigned by JVM?

回答：

In Java, thread priorities are used to indicate the relative importance of threads to the thread scheduler. The Java Virtual Machine (JVM) allows you to set the priority of a thread using the setPriority(int priority) method of the Thread class. Thread priorities are represented by integer values, and they can range from Thread.MIN_PRIORITY to Thread.MAX_PRIORITY.

Here are the different types of thread priorities in Java:

  1. MIN_PRIORITY: This is the lowest priority a thread can have. It is represented by the constant value 1.

    public static final int MIN_PRIORITY = 1;

  2. NORM_PRIORITY: This is the default priority assigned to a thread if no priority is explicitly set. It is represented by the constant value 5.

    public static final int NORM_PRIORITY = 5;

  3. MAX_PRIORITY: This is the highest priority a thread can have. It is represented by the constant value 10.

    public static final int MAX_PRIORITY = 10;

Default Priority

The default priority of a thread assigned by the JVM is NORM_PRIORITY, which has a value of 5. If you create a new thread without specifying a priority, it will automatically be assigned this default value.

Example of Setting Thread Priority

Here is a simple example of how to set thread priorities in Java:

public class ThreadPriorityExample {
    public static void main(String[] args) {
        Thread thread1 = new Thread(() -> {
            System.out.println("Thread 1 is running");
        });
        Thread thread2 = new Thread(() -> {
            System.out.println("Thread 2 is running");
        });

        // Set priorities
        thread1.setPriority(Thread.MIN_PRIORITY); // Set to lowest priority
        thread2.setPriority(Thread.MAX_PRIORITY); // Set to highest priority

        // Start threads
        thread1.start();
        thread2.start();
    }
}

Important Note

It's important to note that thread priority is a hint to the thread scheduler, and the actual behavior can vary between different JVM implementations and operating systems. Therefore, relying solely on thread priorities for critical application behavior is not recommended.

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