时间：2020-11-12 08:57:59 | 栏目：JAVA代码 | 点击：次
使用Runnable实现数据共享，供大家参考，具体内容如下
先上代码：
public class TestThread {
private static final Logger logger = LoggerFactory.getLogger(TestThread.class);
private final class MyRunnable implements Runnable {
private int i;
public MyRunnable() {
this.i = 10;
}
public void run() {
while(i > 0) {
synchronized (this) {
if (i > 0) {
i--;
logger.debug("{} buy one ticket, {} left. ", Thread.currentThread().getName(), i);
}
}
}
}
}
@Test
public void testRunable() throws InterruptedException{
MyRunnable myRunnable = new MyRunnable();
Thread th1 = new Thread(myRunnable);
Thread th2 = new Thread(myRunnable);
th1.start();
th2.start();
th1.join();
th2.join();
}
}
楼上的代码很简单，模拟一个售票系统。通过两个Thread对象开启两条线程同时运行一个MyRunnable实例。
几个注意点：
1. 没有加上synchronised关键词的话，即
public void run() {
while(i > 0) {
if (i > 0) {
i--;
logger.debug("{} buy one ticket, {} left. ", Thread.currentThread().getName(), i);
}
}
}
系统的运行结果：
Thread-1 buy one ticket, 8 left. Thread-2 buy one ticket, 8 left. Thread-2 buy one ticket, 6 left. Thread-1 buy one ticket, 6 left. Thread-2 buy one ticket, 5 left. Thread-1 buy one ticket, 4 left. Thread-2 buy one ticket, 3 left. Thread-1 buy one ticket, 2 left. Thread-2 buy one ticket, 1 left. Thread-1 buy one ticket, 0 left.
可以看到，缺少同步的程序输出明显有问题。
2. 在进入同步代码块之后，还需要对i的值再进行一次判断，即，如果不加if判断：
public void run() {
while(i > 0) {
synchronized (this) {
i--;
logger.debug("{} buy one ticket, {} left. ", Thread.currentThread().getName(), i);
}
}
}
程序的运行结果为：
Thread-2 buy one ticket, 9 left. Thread-2 buy one ticket, 8 left. Thread-2 buy one ticket, 7 left. Thread-2 buy one ticket, 6 left. Thread-2 buy one ticket, 5 left. Thread-2 buy one ticket, 4 left. Thread-2 buy one ticket, 3 left. Thread-2 buy one ticket, 2 left. Thread-2 buy one ticket, 1 left. Thread-2 buy one ticket, 0 left. Thread-1 buy one ticket, -1 left.
可以看出，出现了“多卖”的现象， 所以需要在进入同步代码块中再进行一次if判断。
总结
synchronised用于互斥访问共享变量， 并在同步代码块中使用if判断更新共享变量。