【Java并发编程五】线程的基本使用三

线程的管理

 我们使用ThreadGroup对线程进行管理，ThreadGroup具有三个参数，ThreadGroup、Runnable、String：

public Thread(ThreadGroup group, Runnable target, String name)

 例子：

package myTest;

public class myTest implements Runnable {
    public static void main(String[] args) {
        // 线程组
        ThreadGroup tg = new ThreadGroup("myGroup");
        Thread t1 = new Thread(tg, new myTest(), "Thread1");
        Thread t2 = new Thread(tg, new myTest(), "Thread2");
        t1.start();
        t2.start();
        System.out.println(tg.activeCount());
        tg.list();
    }
    @Override
    public void run() {
        String group = Thread.currentThread().getThreadGroup().getName()+"-"+Thread.currentThread().getName();
        while(true) {
            System.out.println("This is "+group);
            try {
                Thread.sleep(10000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
    }
}
/**
2
java.lang.ThreadGroup[name=myGroup,maxpri=10]
    Thread[Thread1,5,myGroup]
    Thread[Thread2,5,myGroup]
This is myGroup-Thread2
This is myGroup-Thread1
*/

线程的后台

 有些主线程在不断的消耗资源进行运算，而后台线程则负责资源垃圾的回收，等主线程结束以后，后台线程便会自然结束。设置后台线程的方法:

package myTest;

public class myTest {
    public static class test1 implements Runnable {
        @Override
        public void run() {
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
    }
    public static class test2 implements Runnable {
        @Override
        public void run() {
            while (true) {
                System.out.println("I am alive");
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
            }
        }
    }
    public static void main(String[] args) {
        Thread t1 = new Thread(new test1());
        Thread t2 = new Thread(new test2());
        t2.setDaemon(true);
        t1.start();
        t2.start();
    }
}

 线程会在运行后，开始寻找主线程，等待主线程，如果发现没有主线程，或主线程已经结束，只有后台线程才存活，便会结束线程。

线程的优先级

 常用控制着线程的优先级的方法为setPriority()：

package myTest;

public class myTest {
    public static class high implements Runnable {
        static int count = 0;
        @Override
        public void run() {
            while(true) {
                synchronized (myTest.class) {
                    count ++;
                    if(count>10000) {
                        System.out.println("high is win");
                        break;
                    }
                }
            }
        }
    }
    public static class low implements Runnable {
        static int count = 0;
        @Override
        public void run() {
            while (true) {
                synchronized (myTest.class) {
                    count ++;
                    if(count>10000) {
                        System.out.println("low is win");
                        break;
                    }
                }
            }
        }
    }
    public static void main(String[] args) {
        Thread t1 = new Thread(new high());
        Thread t2 = new Thread(new low());
        t1.setPriority(10);
        t2.setPriority(1);
        t1.start();
        t2.start();
    }
}