synchronized是阻塞式同步，在线程竞争激烈的情况下会升级为重量级锁。而volatile可以说是java虚拟机提供的最轻量级的同步机制。
根据Java内存模型，各个线程会将共享变量从主内存中拷贝到工作内存，然后执行引擎会基于工作内存中的数据进行操作处理。线程在工作内存进行操作后何时写到主内存是不确定的。volatile修饰的变量给java虚拟机特殊的约定，线程对volatile变量的修改会立刻被其他线程所感知，不会出现数据脏读的现象，从而保证数据的“可见性”。被volatile修饰的变量确保每个线程能够获取该变量的最新值。
package com.bjsxt.base.sync007;
public class RunThread extends Thread{
private volatile boolean isRunning = true;
private void setRunning(boolean isRunning){
this.isRunning = isRunning;
}
public void run(){
System.out.println("进入run方法.."+Thread.currentThread().getName());
int i = 0;
while(isRunning == true){
//..
// System.out.println("线程是否开启："+isRunning);
}
System.out.println("线程停止.."+Thread.currentThread().getName());
}
public static void main(String[] args) throws InterruptedException {
RunThread rt = new RunThread();
rt.start();
Thread.sleep(10);
rt.setRunning(false);
System.out.println("isRunning的值已经被设置了false.."+Thread.currentThread().getName());
}
}
打印
进入run方法..Thread-0
isRunning的值已经被设置了false..main
线程停止..Thread-0
package com.bjsxt.base.conn008;
import java.util.ArrayList;
import java.util.List;
public class ListAdd1 {
private volatile static List list = new ArrayList();
public void add(){
list.add("bjsxt");
}
public int size(){
return list.size();
}
public static void main(String[] args) {
final ListAdd1 list1 = new ListAdd1();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
try {
for(int i = 0; i <10; i++){
list1.add();
System.out.println("当前线程：" + Thread.currentThread().getName() + "添加了一个元素..");
Thread.sleep(500);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
while(true){
if(list1.size() == 5){
System.out.println("当前线程收到通知：" + Thread.currentThread().getName() + " list size = 5 线程停止..");
throw new RuntimeException();
}
}
}
}, "t2");
t1.start();
t2.start();
}
}
原文：https://www.cnblogs.com/hongyedeboke/p/13332898.html