Java - 线程优先级

Java 中的线程优先级

每个 Java 线程都有一个优先级，它可以帮助操作系统确定线程调度的顺序。您可以获取和设置线程的优先级。Thread 类提供用于处理线程优先级的方法和常量。

优先级较高的线程对程序更重要，应在优先级较低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，并且在很大程度上取决于平台。

Thread 类的内置属性常量

Java 线程优先级范围在 MIN_PRIORITY（常量 1）和 MAX_PRIORITY（常量 10）之间。默认情况下，每个线程都赋予 NORM_PRIORITY（常量 5）优先级。

• MIN_PRIORITY：指定线程可以具有的最低优先级。

• NORM_PRIORITY：指定分配给线程的默认优先级。

• MAX_PRIORITY：指定线程可以具有的最高优先级。

线程优先级设置器和获取器方法

• Thread.getPriority() 方法：此方法用于获取线程的优先级。

• Thread.setPriority() 方法：此方法用于设置线程的优先级，它接受优先级值并使用给定的优先级更新现有优先级。

Java 中线程优先级的示例

在这个例子中，我们展示了一个简单的单线程程序，我们没有声明任何线程，并在程序执行中检查线程名称和优先级。

package com.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();	   
   }
}

输出

Thread Name: main
Thread Priority: 5

更多线程优先级的示例

示例 1

在这个例子中，我们创建了一个 ThreadDemo 类，它扩展了 Thread 类。我们创建了三个线程。每个线程都被分配了一个优先级。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.tutorialspoint;
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 Auto-generated catch block
         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 2

在这个例子中，我们创建了一个 ThreadDemo 类，它扩展了 Thread 类。我们创建了三个线程。由于我们没有设置任何优先级，因此每个线程都具有普通优先级。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.tutorialspoint;
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 Auto-generated catch block
         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