Java 线程优先级与示例

每个 Java 线程都有一个优先级，可帮助操作系统确定线程的调度顺序。

Java 线程优先级在以下范围内介于 MIN_PRIORITY（常量 1）和 MAX_PRIORITY（常量 10）之间。默认情况下，每个线程都被赋予优先级 NORM_PRIORITY（常数为 5）。

具有较高优先级的线程对于程序来说更重要，并且应该在较低优先级的线程之前分配处理器时间。但是，线程优先级不能保证线程执行的顺序，并且在很大程度上依赖于平台。

示例 1

在此示例中，我们将展示一个简单的单线程程序，其中我们使用'没有声明任何线程并在程序执行中检查线程名称和优先级。

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();//默认打印优先级5	   
   }
} 

输出

Thread Name: main
Thread Priority: 5 

示例 2

在此示例中，我们创建了一个继承 Thread 类的 ThreadDemo 类。我们创建了三个线程。每个线程都被分配一个优先级。在 run() 方法中，我们打印优先级，在输出中，它反映在线程执行中。

package com.yxjc123;
class ThreadDemo extends Thread {
   ThreadDemo( ) {
   }
   public void run() {
      System.out.println("Thread Name: " + Thread.currentThread().getName() 
         + ", Thread Priority: " +Thread.currentThread().getPriority());
      for(int i = 4; i > 0; i--) {
         System.out.println("Thread: " + Thread.currentThread().getName() + ", " + i); 
      }
      try {
         Thread.sleep(50);
      } catch (InterruptedException e) {
         // TODO 自动生成的 catch 块
         e.printStackTrace();
      }
   }
   public void start () {
      super.start();
   }
}
public class TestThread {
   public static void main(String args[]) {
      ThreadDemo thread1 = new ThreadDemo();
      ThreadDemo thread2 = new ThreadDemo();
      ThreadDemo thread3 = new ThreadDemo();
      thread1.setPriority(Thread.MAX_PRIORITY);
      thread2.setPriority(Thread.MIN_PRIORITY);
      thread3.setPriority(Thread.NORM_PRIORITY);
      thread1.start();	  
      thread2.start();
      thread3.start();
   }
} 

输出

Thread Name: Thread-2, Thread Priority: 5
Thread Name: Thread-1, Thread Priority: 1
Thread Name: Thread-0, Thread Priority: 10
Thread: Thread-1, 4
Thread: Thread-2, 4
Thread: Thread-1, 3
Thread: Thread-0, 4
Thread: Thread-1, 2
Thread: Thread-2, 3
Thread: Thread-0, 3
Thread: Thread-0, 2
Thread: Thread-0, 1
Thread: Thread-2, 2
Thread: Thread-2, 1
Thread: Thread-1, 1 

示例 3

In在这个例子中，我们创建了一个继承 Thread 类的 ThreadDemo 类。我们创建了三个线程。由于我们没有设置任何优先级，因此每个线程都有一个正常的优先级。在 run() 方法中，我们打印优先级，在输出中，线程以任意顺序执行。

package com.yxjc123;
class ThreadDemo extends Thread {
   ThreadDemo( ) {
   }
   public void run() {
      System.out.println("Thread Name: " + Thread.currentThread().getName() 
         + ", Thread Priority: " +Thread.currentThread().getPriority());
      for(int i = 4; i > 0; i--) {
         System.out.println("Thread: " + Thread.currentThread().getName() + ", " + i); 
      }
      try {
         Thread.sleep(50);
      } catch (InterruptedException e) {
         
         // TODO 自动生成的 catch 块
         e.printStackTrace();
      }
   }
   public void start () {
      super.start();
   }
}
public class TestThread {
   public static void main(String args[]) {
      ThreadDemo thread1 = new ThreadDemo();
      ThreadDemo thread2 = new ThreadDemo();
      ThreadDemo thread3 = new ThreadDemo();
      thread1.start();	  
      thread2.start();
      thread3.start();
   }
} 

输出

Thread Name: Thread-1, Thread Priority: 5
Thread Name: Thread-2, Thread Priority: 5
Thread Name: Thread-0, Thread Priority: 5
Thread: Thread-2, 4
Thread: Thread-1, 4
Thread: Thread-1, 3
Thread: Thread-2, 3
Thread: Thread-0, 4
Thread: Thread-2, 2
Thread: Thread-1, 2
Thread: Thread-2, 1
Thread: Thread-0, 3
Thread: Thread-1, 1
Thread: Thread-0, 2
Thread: Thread-0, 1