An in-depth discussion of the definition and characteristics of Java thread state

In-depth analysis of the definition and characteristics of Java thread state

Introduction:
In Java programming, threads are an important concept. Threads allow us to handle multiple tasks at the same time, improving program execution efficiency. Thread status refers to the different states of a thread at different points in time. This article will provide an in-depth analysis of the definition and characteristics of Java thread status, and provide specific code examples to help readers better understand and apply it.

1. Definition of thread state
In the thread life cycle, the thread may experience multiple states. Java defines 6 thread states, namely: New (new), Runnable (runnable) , Blocked, Waiting, Timed Waiting and Terminated.

1.1 New (new) state
When a thread object is created through the new keyword, but the start() method has not been called, the thread is in the new state. The thread in this state has not yet started execution and does not occupy CPU resources.

1.2 Runnable (runnable) state
When the thread enters the runnable state, it means that the thread is ready and can be scheduled for execution by the JVM. In the runnable state, the thread may be scheduled by the JVM, or it may be blocked and waiting for some reasons.

1.3 Blocked state
When a thread is waiting to acquire a lock to enter a synchronized code block, the thread is in a blocked state. The thread will be temporarily suspended in this state, waiting for other threads to release the lock. Threads will not occupy CPU resources when blocked.

1.4 Waiting (waiting) state
When the thread calls the wait() method, it will enter the waiting state. In the waiting state, the thread will wait until other threads call the notify() or notifyAll() method to wake up the thread. Threads do not occupy CPU resources in the waiting state.

1.5 Timed Waiting state
Similar to the waiting state, when a thread calls a waiting method with a timeout, it will enter the timed waiting state. The thread will wait for a period of time in this state. When the timeout reaches or other threads call the notify() or notifyAll() method, the thread will be awakened. Threads will not occupy CPU resources in the scheduled waiting state.

1.6 Terminated state
When the thread completes execution or terminates due to an exception, the thread enters the terminated state. A thread in the terminated state will no longer perform any tasks.

2. Thread state conversion

2.1 Code example
In order to better understand the thread state conversion, a code example is given below:

public class ThreadStateDemo implements Runnable {
    public void run() {
        synchronized (this) {
            try {
                Thread.sleep(2000);
                wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        ThreadStateDemo obj = new ThreadStateDemo();
        Thread thread = new Thread(obj);

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

        System.out.println("线程状态: " + thread.getState());  // 打印线程状态
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        synchronized (obj) {
            obj.notify();
        }

        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

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

2.2 Analysis Description
In the above code, we created a ThreadStateDemo class that implemented the Runnable interface and implemented the run() method. In the run() method, we use the synchronized keyword to lock the object, and call the sleep() and wait() methods to simulate different state transitions of the thread.

In the main() method, we create a thread object and obtain the thread state through the getState() method. Before the thread starts, the status of the thread is NEW, indicating that the thread is in a new state. After the thread is started, the thread enters the RUNNABLE state, indicating that the thread is in a runnable state. Subsequently, we use the sleep() method to make the thread sleep for 1 second to simulate the running of the thread. Then, wake up the waiting thread through the notify() method. Finally, after the thread execution is completed, the thread enters the terminated state.

By running the above code, we can observe the conversion process of thread state, thereby gaining a deeper understanding of the relationship between thread state and code execution.

Conclusion:
Six thread states are defined in Java, namely New (new), Runnable (runnable), Blocked (blocked), Waiting (waiting), Timed Waiting (timing waiting) and Terminated. With appropriate code examples, we can better understand the definition and characteristics of these states. Understanding thread status helps us better manage and schedule multi-threaded tasks and improve program execution efficiency. In actual development, we should reasonably handle thread state conversion according to business needs and thread interaction rules to achieve code security and efficiency.

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