synchronized(二)

package com.bjsxt.base.sync002;
/**
* 关键字synchronized取得的锁都是对象锁，而不是把一段代码（方法）当做锁，
* 所以代码中哪个线程先执行synchronized关键字的方法，哪个线程就持有该方法所属对象的锁（Lock），
*
* 在静态方法上加synchronized关键字，表示锁定.class类，类一级别的锁（独占.class类）。
* @author alienware
*
*/
public class MultiThread {

private static int num = 0;

/** static */
public static synchronized void printNum(String tag){
try {

if(tag.equals("a")){
num = 100;
System.out.println("tag a, set num over!");
Thread.sleep(1000);
} else {
num = 200;
System.out.println("tag b, set num over!");
}

System.out.println("tag " + tag + ", num = " + num);

} catch (InterruptedException e) {
e.printStackTrace();
}
}

//注意观察run方法输出顺序
public static void main(String[] args) {

//俩个不同的对象
final MultiThread m1 = new MultiThread();
final MultiThread m2 = new MultiThread();

Thread t1 = new Thread(new Runnable() {
public void run() {
m1.printNum("a");
}
});

Thread t2 = new Thread(new Runnable() {

public void run() {
m2.printNum("b");
}
});

t1.start();
t2.start();

}

运行结果为：

tag a, set num over!
tag a, num = 100
tag b, set num over!
tag b, num = 200

}