/*
 author by w3cschool.cc
 LockTest.java
 */
import java.util.Date;
public class LockTest {
  public static String obj1 = "obj1";
  public static String obj2 = "obj2";
  public static void main(String[] args) {
   LockA la = new LockA();
   new Thread(la).start();
   LockB lb = new LockB();
   new Thread(lb).start();
  }
}
class LockA implements Runnable{
  public void run() {
   try {
     System.out.println(new Date().toString() + " LockA 开始执行");
     while(true){
      synchronized (LockTest.obj1) {
        System.out.println(new Date().toString() + " LockA 锁住 obj1");
        Thread.sleep(3000); // 此处等待是给B能锁住机会
        synchronized (LockTest.obj2) {
         System.out.println(new Date().toString() + " LockA 锁住 obj2");
         Thread.sleep(60 * 1000); // 为测试，占用了就不放
        }
      }
     }
   } catch (Exception e) {
     e.printStackTrace();
   }
  }
}
class LockB implements Runnable{
  public void run() {
   try {
     System.out.println(new Date().toString() + " LockB 开始执行");
     while(true){
      synchronized (LockTest.obj2) {
        System.out.println(new Date().toString() + " LockB 锁住 obj2");
        Thread.sleep(3000); // 此处等待是给A能锁住机会
        synchronized (LockTest.obj1) {
         System.out.println(new Date().toString() + " LockB 锁住 obj1");
         Thread.sleep(60 * 1000); // 为测试，占用了就不放
        }
      }
     }
   } catch (Exception e) {
     e.printStackTrace();
   }
  }
}

Tue May 05 10:51:06 CST 2015 LockB 开始执行
Tue May 05 10:51:06 CST 2015 LockA 开始执行
Tue May 05 10:51:06 CST 2015 LockB 锁住 obj2
Tue May 05 10:51:06 CST 2015 LockA 锁住 obj1

/*
 author by w3cschool.cc
 UnLockTest.java
 */
import java.util.Date;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;
public class UnLockTest {
  public static String obj1 = "obj1";
  public static final Semaphore a1 = new Semaphore(1);
  public static String obj2 = "obj2";
  public static final Semaphore a2 = new Semaphore(1);
  public static void main(String[] args) {
   LockAa la = new LockAa();
   new Thread(la).start();
   LockBb lb = new LockBb();
   new Thread(lb).start();
  }
}
class LockAa implements Runnable {
  public void run() {
   try {
     System.out.println(new Date().toString() + " LockA 开始执行");
     while (true) {
      if (UnLockTest.a1.tryAcquire(1, TimeUnit.SECONDS)) {
        System.out.println(new Date().toString() + " LockA 锁住 obj1");
        if (UnLockTest.a2.tryAcquire(1, TimeUnit.SECONDS)) {
         System.out.println(new Date().toString() + " LockA 锁住 obj2");
         Thread.sleep(60 * 1000); // do something
        }else{
         System.out.println(new Date().toString() + "LockA 锁 obj2 失败");
        }
      }else{
        System.out.println(new Date().toString() + "LockA 锁 obj1 失败");
      }
      UnLockTest.a1.release(); // 释放
      UnLockTest.a2.release();
      Thread.sleep(1000); // 马上进行尝试，现实情况下do something是不确定的
     }
   } catch (Exception e) {
     e.printStackTrace();
   }
  }
}
class LockBb implements Runnable {
  public void run() {
   try {
     System.out.println(new Date().toString() + " LockB 开始执行");
     while (true) {
      if (UnLockTest.a2.tryAcquire(1, TimeUnit.SECONDS)) {
        System.out.println(new Date().toString() + " LockB 锁住 obj2");
        if (UnLockTest.a1.tryAcquire(1, TimeUnit.SECONDS)) {
         System.out.println(new Date().toString() + " LockB 锁住 obj1");
         Thread.sleep(60 * 1000); // do something
        }else{
         System.out.println(new Date().toString() + "LockB 锁 obj1 失败");
        }
      }else{
        System.out.println(new Date().toString() + "LockB 锁 obj2 失败");
      }
      UnLockTest.a1.release(); // 释放
      UnLockTest.a2.release();
      Thread.sleep(10 * 1000); // 这里只是为了演示，所以tryAcquire只用1秒，而且B要给A让出能执行的时间，否则两个永远是死锁
     }
   } catch (Exception e) {
     e.printStackTrace();
   }
  }
}

Tue May 05 10:59:13 CST 2015 LockA 开始执行
Tue May 05 10:59:13 CST 2015 LockB 开始执行
Tue May 05 10:59:13 CST 2015 LockB 锁住 obj2
Tue May 05 10:59:13 CST 2015 LockA 锁住 obj1
Tue May 05 10:59:14 CST 2015LockB 锁 obj1 失败
Tue May 05 10:59:14 CST 2015LockA 锁 obj2 失败
Tue May 05 10:59:15 CST 2015 LockA 锁住 obj1
Tue May 05 10:59:15 CST 2015 LockA 锁住 obj2