Discuss the classification of Java thread states and state transfer rules

Exploring the types and conversion rules of Java thread states

A thread is an execution unit in Java that can run independently and execute concurrently with other threads. In Java, threads have multiple states that reflect the behavior and conditions of the thread at different stages. This article will explore the status types and transition rules of Java threads and provide specific code examples.

The main types of Java thread states are as follows:

1. New state (New): The thread is created but has not been started yet.
2. Running status (Runnable): The thread is started and can run, including the status of running and about to or waiting for CPU resources.
3. Blocked state (Blocked): The thread is suspended from execution, usually because it is waiting for a certain condition to occur and cannot continue to execute.
4. Waiting state (Waiting): The thread suspends execution until other threads send it a wake-up notification.
5. Timed Waiting state (Timed Waiting): The thread suspends execution until other threads send it a wake-up notification or the specified time arrives.
6. Termination status (Terminated): The thread has completed execution or exited due to an exception.

The conversion rules between thread states are as follows:

1. New state -> Running state: Call the start() method of the thread object to start the thread.
2. Running status -> Blocking status: The thread is waiting for the release of a lock, or the thread calls the static sleep() method of the Thread class.
3. Running status -> Waiting status: The thread calls the wait() method of the Object class.
4. Running status -> Timing waiting status: The thread calls the static sleep() method of the Thread class and specifies the time.
5. Blocking state -> Running state: The lock is released or the blocked thread is awakened.
6. Waiting state -> Running state: Other threads send wake-up notifications to waiting threads.
7. Timed waiting state -> Running state: Time arrives or other threads send wake-up notifications to the timed waiting thread.
8. Running status -> Termination status: The thread has completed execution or exited due to an exception.

The following is a specific code example that demonstrates the Java thread state conversion process:

public class ThreadStateExample {
    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(() -> {
            try {
                Thread.sleep(1000); // 让线程进入计时等待状态
                synchronized (ThreadStateExample.class) {
                    ThreadStateExample.class.wait(); // 让线程进入等待状态
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });

        System.out.println("线程状态: " + thread.getState()); // 输出：线程状态: NEW

        thread.start();
        System.out.println("线程状态: " + thread.getState()); // 输出：线程状态: RUNNABLE

        Thread.sleep(500); // 等待500毫秒，让线程执行一段时间

        System.out.println("线程状态: " + thread.getState()); // 输出：线程状态: TIMED_WAITING

        synchronized (ThreadStateExample.class) {
            ThreadStateExample.class.notify(); // 唤醒等待线程
        }

        Thread.sleep(500); // 等待500毫秒，让线程执行一段时间

        System.out.println("线程状态: " + thread.getState()); // 输出：线程状态: TERMINATED
    }
}

Run the above code, you can observe the thread state conversion process. By knowing and understanding thread status, we can better control thread behavior and avoid potential threading problems. In actual development, rational use of thread status can improve the efficiency and stability of multi-threaded programs.

Summary:

This article explores the types and conversion rules of Java thread states, and provides specific code examples. Understanding the thread state conversion rules helps us better understand and use multi-threaded programming. When writing multi-threaded programs, we can handle and optimize the different states of threads accordingly. I hope this article will be helpful to everyone’s study and practice.

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