Java基础知识之多线程（2）

线程的休眠

使用方法：public static void sleep(long millis)throws InterruptedException{}
可见该方法有异常抛出，所以要进行异常的处理。

public class A implements Runnable {
    private String name;
    public A(String name) {
        super();
        this.name = name;
    }

    @Override
    public void run() {
        // TODO Auto-generated method stub
        for (int i = 0; i < 10; i++) {
            try {
                Thread.sleep(500);//休眠
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("运行：" + name);
        }
    }
}

测试一下：

public class ATest {
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        A mt1 = new A("线程1");
        A mt2 = new A("线程2");

        new Thread(mt1,"线程111").start();
        System.out.println(Thread.currentThread().getName());
        new Thread(mt2,"线程111").start();
    }
}

线程的优先级

public class MyThreadImplement implements Runnable {
    @Override
    public void run() {
        // TODO Auto-generated method stub
        for (int i = 0; i < 5; i++) {
            try {
                Thread.sleep(500);//休眠
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            //得到当前的线程名称
            System.out.println(Thread.currentThread().getName());
        }
    }
}

测试类：

public class MyThreadImplementTest {
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        MyThreadImplement mt1 = new MyThreadImplement();

        Thread m1 = new Thread(mt1,"线程1");
        Thread m2 = new Thread(mt1,"线程2");
        Thread m3 = new Thread(mt1,"线程3");
        //使用setPriority()方法设置线程优先级
        //传入的参数是 Thread类中的常量，分别表示优先级最高，正常，最低
        m1.setPriority(Thread.MAX_PRIORITY);
        m2.setPriority(Thread.NORM_PRIORITY);
        m3.setPriority(Thread.MIN_PRIORITY);

        m1.start();m2.start();m3.start();
    }
}

线程的中断

调用interrupt()方法可以中断一个正在运行的线程！

线程的同步问题

看一个小例子：

public class TickThread implements Runnable {
    //模拟卖票，共5张
    private int tick = 5;
    @Override
    public void run() {
        // TODO Auto-generated method stub
        for (int i = 0; i < 5; i++) {
            if(this.tick>0){
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                System.out.println("卖票："+tick--);
            }
        }
    }
}

测试类：

public class TickThreadTest {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        TickThread m = new TickThread();
        new Thread(m,"A").start();
        new Thread(m,"B").start();
        new Thread(m,"C").start();
    }
}

通过运行结果发现出现了异常。原因是代码中加入了休眠的操作，线程A正在休眠，线程B运行起来卖掉了当前线程A的票，A休眠结束后，继续卖票，出现了上面的情况。下面通过加入同步解决这个问题。
所谓同步，多个操作在同一个时间段只能有一个在进行，A线程在运行后，就不会
1）同步代码块实现同步
修改后的代码：

public class TickThread implements Runnable {

    private int tick = 5;
    @Override
    public void run() {
        // TODO Auto-generated method stub
        //synchronized声明同步代码块
        synchronized (this) {
            for (int i = 0; i < 5; i++) {
                if(this.tick>0){
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName()+"运行"+tick--);
                }
            }
        }
    }
}

也可以把要同步的代码写成一个方法
修改后的代码：

public class TickThread implements Runnable {

    private int tick = 5;
    @Override
    public void run() {
        // TODO Auto-generated method stub
        //synchronized声明同步代码块
        fun();
    }
    public synchronized void fun(){
        for (int i = 0; i < 5; i++) {
            if(this.tick>0){
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName()+"运行"+tick--);
            }
        }
    }
}

死锁问题

多个线程共享一个数据时需要进行同步，但过多的同步会产生死锁；