Java 主线程与示例

每当我们运行 Java 程序时，主线程都会自动创建。该线程负责java程序的执行。 Java运行时搜索main方法来执行并基于它创建一个主线程。如果我们创建多个线程，那么所有子线程都将从主线程生成。该主线程是要创建的第一个线程，通常是最后一个线程，用于执行关闭任务。

示例 1

在此示例中，我们展示了一个简单的单线程程序，我们在程序执行中不声明任何线程并检查线程名称。

package com.yxjc123;
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();	   
   }
} 

输出

Thread Name: main
Thread Priority: 5 

示例 2

在这个例子中，我们创建了一个继承 Thread 类的 ThreadDemo 类。我们不会向线程传递任何名称，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，当前线程名称打印为 main，同时使用 constructor() 方法调用创建线程。

package com.yxjc123;
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();
   }
} 

输出

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 

示例 3

在此示例中，我们创建了一个扩展 Thread 类的 ThreadDemo 类。我们不会向线程传递任何名称，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是否打印为主线程，而线程是使用 constructor() 方法调用创建的。在 main 方法的末尾，我们打印主线程的状态。

package com.yxjc123;
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");
   }
} 

输出

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，您可以检查主线程是否已在早期阶段完成，但是线程仍在运行并完成了执行。