synchronized和vilatile

第一个程序

public class Test06 implements Runnable{

    public int a = 0;

    public static void main(String[] args) throws InterruptedException {

        Test06 r = new Test06();

        Thread[] t = new Thread[100];

        for(int i = 0;i < 100;i++)

            t[i] = new Thread(r);

        for(int j = 0;j < 100;j++)

            t[j].start();

        Thread.currentThread().sleep(2000);

        System.out.println(r.a);

    }

    @Override

    public  void run() {

        int b = a+1;

        try {

            Thread.currentThread().sleep(10);

        } catch (InterruptedException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

        a = b;

    }

}

输出为？

第二个程序

public class Test06 implements Runnable{

    public int a = 0;

    public static void main(String[] args) throws InterruptedException {

        Test06 r = new Test06();

        Thread[] t = new Thread[100];

        for(int i = 0;i < 100;i++)

            t[i] = new Thread(r);

        for(int j = 0;j < 100;j++)

            t[j].start();

        Thread.currentThread().sleep(2000);

        System.out.println(r.a);

    }

    @Override

    public  synchronized void run() {

        int b = a+1;

        try {

            Thread.currentThread().sleep(10);

        } catch (InterruptedException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

        a = b;

    }

}

输出为？

第三个程序

public class Test06 implements Runnable{

    public volatile int a = 0;

    public static void main(String[] args) throws InterruptedException {

        Test06 r = new Test06();

        Thread[] t = new Thread[100];

        for(int i = 0;i < 100;i++)

            t[i] = new Thread(r);

        for(int j = 0;j < 100;j++)

            t[j].start();

        Thread.currentThread().sleep(2000);

        System.out.println(r.a);

    }

    @Override

    public  void run() {

        int b = a+1;

        try {

            Thread.currentThread().sleep(10);

        } catch (InterruptedException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

        a = b;

    }

}

输出为？

三个程序中只有第二个能保证输出的为100