Java 简明教程

Java - Main Thread

Main Thread in Java

每当运行 Java 程序时，主线程会自动创建。此线程负责执行 Java 程序。Java 运行时搜索主方法进行执行并基于此创建一个主线程。如果我们创建多个线程，则所有子线程都会从主线程派生。此主线程是第一个创建的线程，通常是最后一个线程，并且用于执行关闭任务。

How to Control Main Thread?

当程序启动时，JVM 会自动创建主线程。但是，可以通过使用不同的线程方法和技术来控制主线程。

以下是一些用于控制主线程的方法。

Example of Java Main Thread

在此示例中，我们演示了一个简单的单线程程序，其中我们未声明任何线程并在程序执行中检查线程名称。

package com.tutorialspoint;
public class TestThread {
   public void printName() {
	   System.out.println("Thread Name: " + Thread.currentThread().getName());
	   System.out.println("Thread Priority: " +Thread.currentThread().getPriority());
   }
   public static void main(String args[]) {
	   TestThread thread = new TestThread();
	   thread.printName();
   }
}

Thread Name: main
Thread Priority: 5

More Example of Main Thread

Example

在此示例中，我们创建了一个 ThreadDemo 类，该类扩展了 Thread 类。我们不向 Thread 传递任何名称，它将打印系统分配给线程的默认名称。在 main 方法中，我们创建了两个线程。在输出中，您可以检查当前线程名称已打印为 main，而线程是使用 constructor() 方法调用创建的。

package com.tutorialspoint;
class ThreadDemo extends Thread {
   ThreadDemo( ) {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: New");
   }
   public void run() {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Running");
      for(int i = 4; i > 0; i--) {
         System.out.println("Thread: " + Thread.currentThread().getName() + ", " + i);
      }
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Dead");
   }
   public void start () {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Start");
      super.start();
   }
}
public class TestThread {
   public static void main(String args[]) {
	  ThreadDemo thread1 = new ThreadDemo();
	  ThreadDemo thread2 = new ThreadDemo();
	  thread1.start();
	  thread2.start();
   }
}

Thread: main, State: New
Thread: main, State: New
Thread: main, State: Start
Thread: main, State: Start
Thread: Thread-0, State: Running
Thread: Thread-0, 4
Thread: Thread-0, 3
Thread: Thread-1, State: Running
Thread: Thread-1, 4
Thread: Thread-0, 2
Thread: Thread-1, 3
Thread: Thread-0, 1
Thread: Thread-1, 2
Thread: Thread-0, State: Dead
Thread: Thread-1, 1
Thread: Thread-1, State: Dead

Example 2

在此示例中，我们创建了一个 ThreadDemo 类，该类扩展了 Thread 类。我们不向 Thread 传递任何名称，它将打印系统分配给线程的默认名称。在 main 方法中，我们创建了两个线程。在输出中，您可以检查当前线程名称已打印为 main，而线程是使用 constructor() 方法调用创建的。在 main 方法的最后，我们打印主线程的状态。

package com.tutorialspoint;
class ThreadDemo extends Thread {
   ThreadDemo( ) {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: New");
   }
   public void run() {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Running");
      for(int i = 4; i > 0; i--) {
         System.out.println("Thread: " + Thread.currentThread().getName() + ", " + i);
      }
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Dead");
   }
   public void start () {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Start");
      super.start();
   }
}
public class TestThread {
   public static void main(String args[]) {
	  ThreadDemo thread1 = new ThreadDemo();
	  ThreadDemo thread2 = new ThreadDemo();
	  thread1.start();
	  thread2.start();
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Dead");
   }
}

Thread: main, State: New
Thread: main, State: New
Thread: main, State: Start
Thread: main, State: Start
Thread: Thread-0, State: Running
Thread: main, State: Dead
Thread: Thread-1, State: Running
Thread: Thread-0, 4
Thread: Thread-1, 4
Thread: Thread-1, 3
Thread: Thread-1, 2
Thread: Thread-1, 1
Thread: Thread-1, State: Dead
Thread: Thread-0, 3
Thread: Thread-0, 2
Thread: Thread-0, 1
Thread: Thread-0, State: Dead

在此输出中，您可以检查到主线程在早期阶段已完成，但线程仍在运行并已完成其执行。