Volatile 修饰的成员变量在每次被线程访问时，都强制从共享内存中重新读取该成员变量的值。而且，当成员变量发生变化时，会强制线程将变化值回写到共享内存。这样在任何时刻，两个不同的线程总是看到某个成员变量的同一个值。
一个volatile对象引用可能是null。
（1）Java程序代码
package niukewang; public class volatile_Test { public static void main(String args[]) { MyRunnable r = new MyRunnable(); Thread t1 = new Thread(r);
t1.start(); try { Thread.sleep(2); r.stopThread(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } } class MyRunnable implements Runnable { private volatile boolean active; public void run() { active = true; while (active) // 第一行 { // 代码 System.out.println("Print the line"); } } public void stopThread() { System.out.println("Set to false"); active = false; // 第二行 } }
只有当调用stopThread时候，设置了ative为false的时候，然后线程获取了false的值，会停止第一行中内容的输出。
（2）输出结果。
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