volatile修饰符
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。
Print the line
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Print the line
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Print the line
Print the line
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Print the line
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Print the line
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Print the line
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Print the line
Print the line
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Print the line
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Print the line
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Print the line
Print the line
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Print the line
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Print the line
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Print the line
Print the line
Print the line
Print the line
Print the line
Print the line
Set to false
Print the line
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