Java volatile 的测试（Java代码实战-004）

 

package Threads; /** * Created by xfyou 2018/5/21 16:07. */
public class VolatileTest { private static volatile int MY_INT = 0; /** * 主线程启动2个测试子线程 * * @param args null */
    public static void main(String[] args) { new ChangeListener().start(); new ChangeMaker().start(); } /** * 此线程负责对MY_INT值改变的侦听，如果有改变就会打印出来 */
    static class ChangeListener extends Thread { @Override public void run() { int local_value = MY_INT; while (local_value < 5) { if (local_value != MY_INT) { System.out.println("Got Change for MY_INT : " + MY_INT); local_value = MY_INT; } } } } /** * 此线程负责改变MY_INT的值 */
    static class ChangeMaker extends Thread { @Override public void run() { int local_value = MY_INT; while (MY_INT < 5) { System.out.println("Incrementing MY_INT to " + (local_value + 1)); MY_INT = ++local_value; try { Thread.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); } } } } }

当使用volatile时，修改线程对static MY_INT值的修改，另一个侦听线程（读MY_INT的值）是可以及时读取到的，输出结果如下：

Incrementing MY_INT to 1 Got Change for MY_INT : 1 Incrementing MY_INT to 2 Got Change for MY_INT : 2 Incrementing MY_INT to 3 Got Change for MY_INT : 3 Incrementing MY_INT to 4 Got Change for MY_INT : 4 Incrementing MY_INT to 5 Got Change for MY_INT : 5

当不使用volatile时，修改线程对static MY_INT值的修改，另一个侦听线程（读MY_INT的值）可能完全读取不到（无感知），可能的输出结果如下：

Incrementing MY_INT to 1 Incrementing MY_INT to 2 Incrementing MY_INT to 3 Incrementing MY_INT to 4 Incrementing MY_INT to 5