一个解释volatile关键字最好的例子

小例子

public class VolatileTest {
    private static volatile int INIT_VALUE = 0;
    private final static  int MAX_VALUE = 5;

    public static void main(String[] args) {
        // 读线程
        new Thread(()->{
            int localValue = INIT_VALUE;
            while (localValue < MAX_VALUE){
                if (localValue != INIT_VALUE){
                    System.out.println("The value update to \t" + INIT_VALUE);
                    localValue = INIT_VALUE;
                }

            }
        }, "reader").start();

        // 更新线程
        new Thread(()->{
            int localValue = INIT_VALUE;
            while (localValue < MAX_VALUE){
                System.out.println("update value update to \t" + (++localValue));
                INIT_VALUE = localValue;
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "update").start();
    }
}

输出结果：

若是不加volatile关键字呢？

package wangwenjun.phase2.chapter03;

import java.util.concurrent.TimeUnit;

public class VolatileTest {
    private static int INIT_VALUE = 0;
    private final static  int MAX_VALUE = 5;

    public static void main(String[] args) {
        // 读线程
        new Thread(()->{
            try {
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            int localValue = INIT_VALUE;
            while (localValue < MAX_VALUE){
                if (localValue != INIT_VALUE){
                    System.out.println("The value update to \t" + INIT_VALUE);
                    localValue = INIT_VALUE;
                }

            }
        }, "reader").start();

        // 更新线程
        new Thread(()->{
            int localValue = INIT_VALUE;
            while (localValue < MAX_VALUE){
                System.out.println("update value update to \t" + (++localValue));
                INIT_VALUE = localValue;
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "update").start();
    }
}

输出结果：