从第二段代码可知，同步的关键是多个线程对象竞争同一个共享资源即可，上面的代码中是通过外部创建共享资源，然后传递到线程中来实现。我们也可以利用类成员变量被所有类的实例所共享这一特性，因此可以将lock用静态成员对象来实现，代码如下所示：修改MyThread.java类如下
package com.clark.thread;
public class MyThread implements Runnable{
private int threadId;
private static Object object = new Object();//线程之间竞争使用的对象锁
public MyThread(int id){
this.threadId = id;
}
@Override
public void run() {
<strong>/**
* 将这个object对象的引用传递给每一个线程对象的lock成员变量
* 从而每个线程的lock成员都指向同一个Object对象
* 这样就可以让线程去竞争这个唯一的共享的对象锁，从而实现同步。
*/</strong>
synchronized(object){
for (int i = 0; i < 100; i++) {
if(i % 10 ==0){
System.out.println();
}
System.out.print("Thread ID:"+this.threadId+":"+i+" ");
}
}
}
}
结果如下：
Thread ID:0:0 Thread ID:0:1 Thread ID:0:2 Thread ID:0:3 Thread ID:0:4 Thread ID:0:5 Thread ID:0:6 Thread ID:0:7 Thread ID:0:8 Thread ID:0:9
Thread ID:0:10 Thread ID:0:11 Thread ID:0:12 Thread ID:0:13 Thread ID:0:14 Thread ID:0:15 Thread ID:0:16 Thread ID:0:17 Thread ID:0:18 Thread ID:0:19
Thread ID:0:20 Thread ID:0:21 Thread ID:0:22 Thread ID:0:23 Thread ID:0:24 Thread ID:0:25 Thread ID:0:26 Thread ID:0:27 Thread ID:0:28 Thread ID:0:29
Thread ID:0:30 Thread ID:0:31 Thread ID:0:32 Thread ID:0:33 Thread ID:0:34 Thread ID:0:35 Thread ID:0:36 Thread ID:0:37 Thread ID:0:38 Thread ID:0:39
再来看第一段代码，实例方法中加入sychronized关键字封锁的是this对象本身，而在静态方法中加入sychronized关键字封锁的就是类本身。静态方法是所有类实例对象所共享的，因此线程对象在访问此静态方法时是互斥访问的，从而可以实现线程的同步，代码如下所示：
package com.clark.thread;
public class MyThread implements Runnable{
private int threadId;
public MyThread(int id){
this.threadId = id;
}
@Override
public void run() {
start(this.threadId);
}
private static synchronized void start(int threadId2) {
for (int i = 0; i < 100; i++) {
if(i % 10 == 0){
System.out.println();
}
System.out.print("Thread ID:"+threadId2+":"+i+" ");
}
}
}
结果如下=========
Thread ID:0:0 Thread ID:0:1 Thread ID:0:2 Thread ID:0:3 Thread ID:0:4 Thread ID:0:5 Thread ID:0:6 Thread ID:0:7 Thread ID:0:8 Thread ID:0:9 Thread ID:0:10 Thread ID:0:11 Thread ID:0:12 Thread ID:0:13 Thread ID:0:14 Thread ID:0:15 Thread ID:0:16 Thread ID:0:17 Thread ID:0:18 Thread ID:0:19 Thread ID:0:20 Thread ID:0:21 Thread ID:0:22 Thread ID:0:23 Thread ID:0:24 Thread ID:0:25 Thread ID:0:26 Thread ID:0:27 Thread ID:0:28 Thread ID:0:29 Thread ID:0:30 Thread ID:0:31 Thread ID:0:32 Thread ID:0:33 Thread ID:0:34 Thread ID:0:35 Thread ID:0:36 Thread ID:0:37 Thread ID:0:38 Thread ID:0:39 Thread ID:0:40 Thread ID:0:41 Thread ID:0:42 Thread ID:0:43 Thread ID:0:44 Thread ID:0:45 Thread ID:0:46 Thread ID:0:47 Thread ID:0:48 Thread ID:0:49 Thread ID:0:50 Thread ID:0:51 Thread ID:0:52 Thread ID:0:53 Thread ID:0:54 Thread ID:0:55 Thread ID:0:56 Thread ID:0:57 Thread ID:0:58 Thread ID:0:59
Java1.5后的多线程框架
Java多线程和同步的理解