线程的优先级、继承性、守护线程

线程的优先级、继承性、守护线程

1.线程的优先级

线程的优先级越高，越有可能先执行而已（仅为建议）

1.1 设置优先级

public final void setPriority(int newPriority)

 

1.2 取得优先级

public final int getPriority()

 

1.2.1 JDK内置优先级

1.最高优先级 : public final static int MAX_PRIORITY=10;

2.中等优先级：public final static int NORM_PRIORITY=5;

3.最低优先级： public final static int MIN_PRIORITY=1;

代码实现：设置优先级

package ThreadTest.PriorityTest;

public class PriorityDemo {
    public static void main(String[] args) {
        MyThread myThread = new MyThread();
        Thread t1 = new Thread(myThread);
        Thread t2 = new Thread(myThread);
        Thread t3 = new Thread(myThread);
        //设置优先级
        t1.setPriority(Thread.MAX_PRIORITY);
        t2.setPriority(Thread.NORM_PRIORITY);
        t3.setPriority(Thread.MIN_PRIORITY);
        t1.start();
        t2.start();
        t3.start();
    }
}
class MyThread implements Runnable{

    @Override
    public void run() {
        for(int i=0;i<5;i++){
            System.out.println("当前线程为"+Thread.currentThread().getName()+",i="+i);
        }
    }
}

 

主方法是一个中等优先级；

2.线程的继承性

若在一个线程中创建了子线程，默认子线程与父线程的优先级相同

比如在A线程中启动了B线程，那么B的优先级和A一样；

package ThreadTest.ThreadExtends;

class A implements Runnable{

    @Override
    public void run() {
        System.out.println("A的优先级："+Thread.currentThread().getPriority());
        Thread thread = new Thread(new B());
        thread.start();
    }
}
class B implements Runnable{

    @Override
    public void run() {
        System.out.println("B的优先级："+Thread.currentThread().getPriority());
    }
}
public class ThreadExtendsDemo {
    public static void main(String[] args) {
        Thread thread = new Thread(new A());
        //将A线程的优先级设置为最高优先级
        thread.setPriority(Thread.MAX_PRIORITY);
        thread.start();
    }
}

 

3.守护线程

java中线程分为两类：

用户线程、守护线程 通过isDaemon()方法区分他们：如果返回false，则说明该线程是“用户线程”；如果返回true，则说明该线程是“守护线程”. 守护线程为陪伴线程，只要JVM中存在由任何一个用户线程没有终止，守护线程就一直在工作。 **默认创建的线程都有用户线程，主线程也为用户线程。**通过setDaemon（true）将线程对象设置为守护线程。

典型的守护线程：垃圾回收线程（随着线程开始而开始，随着线程结束而结束）

package ThreadTest.DaemonTest;

public class DaemonDemo {
    public static void main(String[] args) throws InterruptedException {
        Thread thread1 = new Thread(new A(), "子线程A");
        //将线程A 设置为守护线程 ，此语句必须在start方法之前执行
        thread1.setDaemon(true);
        thread1.start();

        Thread thread2 = new Thread(new A(), "子线程B");
        thread2.start();
        Thread.sleep(3000);
        //中断非守护线程
        thread2.interrupt();
        Thread.sleep(10000);
        System.out.println("代码结束");
    }
}

class A implements Runnable {
    private int i;

    @Override
    public void run() {
        try {
            while (true) {
                i++;
                System.out.println("线程名称" + Thread.currentThread().getName() +
                        ",i=" + i + "，是否为守护线程" + Thread.currentThread().isDaemon());
                Thread.sleep(1000);
             }
        } catch (InterruptedException e) {
            System.out.println("线程名称：" + Thread.currentThread().getName() + "线程中断");
        }
    }
}