既然有關監視器monitor的概念比較難，大家怎麼解釋的都有。首先我給出一下java的官方文件，也是最權威的解釋：
Synchronizationis built around an internal entity known as the intrinsic lock ormonitor lock. (The API specification often refers to this entity simplyas a "monitor.")，Every object has an intrinsic lock associated with it.By convention, a thread that needs exclusive and consistent access toan object's fields has to acquire the object's intrinsic lock beforeaccessing them, and then release the intrinsic lock when it's done withthem.

源自：

http://docs.oracle.com/javase/tutorial/essential/concurrency/locksync.html

根據官方文件，我來說說我的看法。馬克-to-win： synchronized工作機制是這樣的：Java中每個物件都有一把鎖與之相關聯，鎖控制著物件的synchronized程式碼。一個要執行物件的synchronized程式碼的執行緒必須先獲得那個物件的鎖。有點兒監控（monitor）的感覺嗎？

synchronized關鍵字使用方式有兩種：synchronized方法和synchronized塊。以下會給出例子：
例1.9.3-本章原始碼class A {
public synchronized void f1() {
for (int i = 0; i < 3; i++) {
try {
Thread.sleep(1000);
} catch (Exception e) {
}
System.out.println("i = " + i);
}
}
}

class MyThread extends Thread {
A a;

public MyThread(A a) {
this.a = a;
}
public void run() {
a.f1();
}
}

public class TestMark_to_win {
public static void main(String[] args) {
A a = new A();。。。。。。。。。。。。。。。。。詳情請進：

http://www.mark-to-win.com/JavaBeginner/JavaBeginner6_web.html#relationshipOfSynchronizedLockandmonitor