Java - 线程生命周期

Java中线程的生命周期

Java 中线程的生命周期是指线程经历的各种状态。例如，线程诞生、启动、运行，然后死亡。Thread 类定义了线程的生命周期和各种状态。

Java 线程生命周期流程图

下图显示了线程的完整生命周期。

Java中线程生命周期的状态

以下是生命周期的阶段：

• 新建 - 新线程从新建状态开始其生命周期。它保持在此状态，直到程序启动线程。它也称为新生线程。

• 可运行 - 新生线程启动后，线程变为可运行状态。处于此状态的线程被认为正在执行其任务。

• 等待 - 有时，当线程等待另一个线程执行任务时，线程会转换到等待状态。只有当另一个线程发出信号让等待线程继续执行时，线程才会转换回可运行状态。

• 计时等待 - 可运行线程可以进入计时等待状态，持续指定的间隔时间。处于此状态的线程在其时间间隔到期或其等待的事件发生时转换回可运行状态。

• 终止（死亡） - 可运行线程在完成其任务或以其他方式终止时进入终止状态。

演示线程状态的 Java 示例

在这个例子中，我们通过扩展 Thread 类来创建两个线程。我们打印线程的每个状态。当创建线程对象时，其状态为 NEW；当调用start() 方法时，状态为 START；当调用run() 方法时，状态为 RUNNING；当线程完成 run() 方法的处理后，它进入 DEAD 状态。

package com.tutorialspoint;
class ThreadDemo extends Thread {
   private Thread t;
   private String threadName;
   ThreadDemo( String name) {
      threadName = name;
      System.out.println("Thread: " + threadName + ", " + "State: New");
   }
   public void run() {
      System.out.println("Thread: " + threadName + ", " + "State: Running");
      for(int i = 4; i > 0; i--) {
         System.out.println("Thread: " + threadName + ", " + i);
      }
      System.out.println("Thread: " + threadName + ", " + "State: Dead");
   }
   public void start () {
      System.out.println("Thread: " + threadName + ", " + "State: Start");
      if (t == null) {
         t = new Thread (this, threadName);
         t.start ();
      }
   }
}
public class TestThread {
   public static void main(String args[]) {
      ThreadDemo thread1 = new ThreadDemo( "Thread-1");
      ThreadDemo thread2 = new ThreadDemo( "Thread-2");
      thread1.start();
      thread2.start();
   }   
}

输出

Thread: Thread-1, State: New
Thread: Thread-2, State: New
Thread: Thread-1, State: Start
Thread: Thread-2, State: Start
Thread: Thread-1, State: Running
Thread: Thread-2, State: Running
Thread: Thread-2, 4
Thread: Thread-2, 3
Thread: Thread-2, 2
Thread: Thread-2, 1
Thread: Thread-2, State: Dead
Thread: Thread-1, 4
Thread: Thread-1, 3
Thread: Thread-1, 2
Thread: Thread-1, 1
Thread: Thread-1, State: Dead

更多关于线程生命周期和状态的示例

示例 1

在这个例子中，我们使用sleep() 方法来引入一些处理延迟，并展示使用线程的并行处理。我们通过扩展 Thread 类来创建两个线程。我们打印线程的每个状态。当创建线程对象时，其状态为 NEW；当调用 start() 方法时，状态为 START；当调用 run() 方法时，状态为 RUNNING；如果调用 sleep()，则线程进入 WAITING 状态；当线程完成 run() 方法的处理后，它进入 DEAD 状态。

package com.tutorialspoint;
class ThreadDemo extends Thread {
   private Thread t;
   private String threadName;
   ThreadDemo( String name) {
      threadName = name;
      System.out.println("Thread: " + threadName + ", " + "State: New");
   }
   public void run() {
      System.out.println("Thread: " + threadName + ", " + "State: Running");
      try {
         for(int i = 4; i > 0; i--) {
            System.out.println("Thread: " + threadName + ", " + i);
            // Let the thread sleep for a while.
            System.out.println("Thread: " + threadName + ", " + "State: Waiting");
            Thread.sleep(50);
         }
      } catch (InterruptedException e) {
         System.out.println("Thread " +  threadName + " interrupted.");
      }
      System.out.println("Thread: " + threadName + ", " + "State: Dead");
   }

   public void start () {
      System.out.println("Thread: " + threadName + ", " + "State: Start");
      if (t == null) {
         t = new Thread (this, threadName);
         t.start ();
      }
   }
}
public class TestThread {
   public static void main(String args[]) {
      ThreadDemo thread1 = new ThreadDemo( "Thread-1");
      ThreadDemo thread2 = new ThreadDemo( "Thread-2");
      thread1.start();
      thread2.start();
   }   
}

输出

Thread: Thread-1, State: New
Thread: Thread-2, State: New
Thread: Thread-1, State: Start
Thread: Thread-2, State: Start
Thread: Thread-1, State: Running
Thread: Thread-1, 4
Thread: Thread-1, State: Waiting
Thread: Thread-2, State: Running
Thread: Thread-2, 4
Thread: Thread-2, State: Waiting
Thread: Thread-1, 3
Thread: Thread-2, 3
Thread: Thread-2, State: Waiting
Thread: Thread-1, State: Waiting
Thread: Thread-2, 2
Thread: Thread-1, 2
Thread: Thread-1, State: Waiting
Thread: Thread-2, State: Waiting
Thread: Thread-2, 1
Thread: Thread-2, State: Waiting
Thread: Thread-1, 1
Thread: Thread-1, State: Waiting
Thread: Thread-2, State: Dead
Thread: Thread-1, State: Dead

示例 2

在这个例子中，我们通过实现 Runnable 类来创建两个线程。我们打印线程的每个状态。当创建线程对象时，其状态为 NEW；当调用 start() 方法时，状态为 START；当调用 run() 方法时，状态为 RUNNING；如果调用 sleep()，则线程进入 WAITING 状态；当线程完成 run() 方法的处理后，它进入 DEAD 状态。

package com.tutorialspoint;
class ThreadDemo implements Runnable {
   private Thread t;
   private String threadName;
   ThreadDemo( String name) {
      threadName = name;
      System.out.println("Thread: " + threadName + ", " + "State: New");
   }
   public void run() {
      System.out.println("Thread: " + threadName + ", " + "State: Running");
      try {
         for(int i = 4; i > 0; i--) {
            System.out.println("Thread: " + threadName + ", " + i);
            // Let the thread sleep for a while.
            System.out.println("Thread: " + threadName + ", " + "State: Waiting");
            Thread.sleep(50);
         }
      } catch (InterruptedException e) {
         System.out.println("Thread " +  threadName + " interrupted.");
      }
      System.out.println("Thread: " + threadName + ", " + "State: Dead");
   }

   public void start () {
      System.out.println("Thread: " + threadName + ", " + "State: Start");
      if (t == null) {
         t = new Thread (this, threadName);
         t.start ();
      }
   }
}
public class TestThread {
   public static void main(String args[]) {
      ThreadDemo thread1 = new ThreadDemo( "Thread-1");
      ThreadDemo thread2 = new ThreadDemo( "Thread-2");
      thread1.start();
      thread2.start();
   }   
}

输出

Thread: Thread-1, State: New
Thread: Thread-2, State: New
Thread: Thread-1, State: Start
Thread: Thread-2, State: Start
Thread: Thread-1, State: Running
Thread: Thread-1, 4
Thread: Thread-1, State: Waiting
Thread: Thread-2, State: Running
Thread: Thread-2, 4
Thread: Thread-2, State: Waiting
Thread: Thread-1, 3
Thread: Thread-2, 3
Thread: Thread-2, State: Waiting
Thread: Thread-1, State: Waiting
Thread: Thread-2, 2
Thread: Thread-1, 2
Thread: Thread-1, State: Waiting
Thread: Thread-2, State: Waiting
Thread: Thread-2, 1
Thread: Thread-2, State: Waiting
Thread: Thread-1, 1
Thread: Thread-1, State: Waiting
Thread: Thread-2, State: Dead
Thread: Thread-1, State: Dead