synchronized(this)、synchronized(class)与synchronized(Object)的区别

在多线程开发中，我们经常看到synchronized(this)、synchronized(*.class)与synchronized(任意对象)这几种类型同步方法。但是是否知道这几种写法有什么区别了？下面根据代码来分析：

synchronized代码块间的同步性

[java] view plain copy print?
  1. package com.zwz.thread.demo1;  
  2.   
  3. public class ObjectService {  
  4.     public void serviceMethodA(){  
  5.         try {  
  6.             synchronized (this) {  
  7.                 System.out.println("A begin time="+System.currentTimeMillis());  
  8.                 Thread.sleep(2000);  
  9.                 System.out.println("A end   time="+System.currentTimeMillis());  
  10.             }  
  11.         } catch (InterruptedException e) {  
  12.             e.printStackTrace();  
  13.         }  
  14.     }  
  15.     public void serviceMethodB(){  
  16.         synchronized (this) {  
  17.             System.out.println("B begin time="+System.currentTimeMillis());  
  18.             System.out.println("B end   time="+System.currentTimeMillis());  
  19.         }  
  20.     }  
  21. }  
package com.zwz.thread.demo1;

public class ObjectService {
	public void serviceMethodA(){
		try {
			synchronized (this) {
				System.out.println("A begin time="+System.currentTimeMillis());
				Thread.sleep(2000);
				System.out.println("A end   time="+System.currentTimeMillis());
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
	public void serviceMethodB(){
		synchronized (this) {
			System.out.println("B begin time="+System.currentTimeMillis());
			System.out.println("B end   time="+System.currentTimeMillis());
		}
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo1;  
  2.   
  3. public class ThreadA extends Thread {  
  4.     private ObjectService objectService;  
  5.     public ThreadA(ObjectService objectService){  
  6.         super();  
  7.         this.objectService=objectService;  
  8.     }  
  9.     @Override  
  10.     public void run() {  
  11.         super.run();  
  12.         objectService.serviceMethodA();  
  13.     }  
  14. }  
package com.zwz.thread.demo1;

public class ThreadA extends Thread {
	private ObjectService objectService;
	public ThreadA(ObjectService objectService){
		super();
		this.objectService=objectService;
	}
	@Override
	public void run() {
		super.run();
		objectService.serviceMethodA();
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo1;  
  2.   
  3. public class ThreadB extends Thread {  
  4.     private ObjectService objectService;  
  5.     public ThreadB(ObjectService objectService){  
  6.         super();  
  7.         this.objectService=objectService;  
  8.     }  
  9.     @Override  
  10.     public void run() {  
  11.         super.run();  
  12.         objectService.serviceMethodB();  
  13.     }  
  14. }  
package com.zwz.thread.demo1;

public class ThreadB extends Thread {
	private ObjectService objectService;
	public ThreadB(ObjectService objectService){
		super();
		this.objectService=objectService;
	}
	@Override
	public void run() {
		super.run();
		objectService.serviceMethodB();
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo1;  
  2.   
  3. public class MainTest {  
  4.     public static void main(String[] args) {  
  5.         ObjectService service=new ObjectService();  
  6.         ThreadA a=new ThreadA(service);  
  7.         a.setName("a");  
  8.         a.start();  
  9.         ThreadB b=new ThreadB(service);  
  10.         b.setName("b");  
  11.         b.start();  
  12.     }  
  13. }  
package com.zwz.thread.demo1;

public class MainTest {
	public static void main(String[] args) {
		ObjectService service=new ObjectService();
		ThreadA a=new ThreadA(service);
		a.setName("a");
		a.start();
		ThreadB b=new ThreadB(service);
		b.setName("b");
		b.start();
	}
}

运行结果：

结论：

当一个线程访问ObjectService的一个synchronized (this)同步代码块时，其它线程对同一个ObjectService中其它的synchronized (this)同步代码块的访问将是堵塞，这说明synchronized (this)使用的对象监视器是一个。

验证synchronized (this)代码块是锁定当前对象

[java] view plain copy print?
  1. package com.zwz.thread.demo2;  
  2.   
  3. public class ObjectService {  
  4.     public void objectMethodA(){  
  5.         System.out.println("run----objectMethodA");  
  6.     }  
  7.     public void objectMethodB(){  
  8.         synchronized (this) {  
  9.             try {  
  10.                 for (int i = 1; i <= 10; i++) {  
  11.                     System.out.println("synchronized thread name:"+Thread.currentThread().getName()+"-->i="+i);  
  12.                     Thread.sleep(1000);  
  13.                 }  
  14.             } catch (InterruptedException e) {  
  15.                     e.printStackTrace();  
  16.             }  
  17.         }  
  18.     }  
  19. }  
package com.zwz.thread.demo2;

public class ObjectService {
	public void objectMethodA(){
		System.out.println("run----objectMethodA");
	}
	public void objectMethodB(){
		synchronized (this) {
			try {
				for (int i = 1; i <= 10; i++) {
					System.out.println("synchronized thread name:"+Thread.currentThread().getName()+"-->i="+i);
					Thread.sleep(1000);
				}
			} catch (InterruptedException e) {
					e.printStackTrace();
			}
		}
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo2;  
  2.   
  3. public class ThreadA extends Thread {  
  4.     private ObjectService objectService;  
  5.   
  6.     public ThreadA(ObjectService objectService) {  
  7.         super();  
  8.         this.objectService = objectService;  
  9.     }  
  10.     @Override  
  11.     public void run() {  
  12.         super.run();  
  13.         objectService.objectMethodA();  
  14.     }  
  15. }  
package com.zwz.thread.demo2;

public class ThreadA extends Thread {
	private ObjectService objectService;

	public ThreadA(ObjectService objectService) {
		super();
		this.objectService = objectService;
	}
	@Override
	public void run() {
		super.run();
		objectService.objectMethodA();
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo2;  
  2.   
  3. public class ThreadB extends Thread {  
  4.     private ObjectService objectService;  
  5.   
  6.     public ThreadB(ObjectService objectService) {  
  7.         super();  
  8.         this.objectService = objectService;  
  9.     }  
  10.     @Override  
  11.     public void run() {  
  12.         super.run();  
  13.         objectService.objectMethodB();  
  14.     }  
  15. }  
package com.zwz.thread.demo2;

public class ThreadB extends Thread {
	private ObjectService objectService;

	public ThreadB(ObjectService objectService) {
		super();
		this.objectService = objectService;
	}
	@Override
	public void run() {
		super.run();
		objectService.objectMethodB();
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo2;  
  2.   
  3. public class MainTest {  
  4.     public static void main(String[] args) throws InterruptedException {  
  5.         ObjectService service=new ObjectService();  
  6.         ThreadB b=new ThreadB(service);  
  7.         b.start();  
  8.         Thread.sleep(2000);  
  9.         ThreadA a=new ThreadA(service);  
  10.         a.start();  
  11.     }  
  12. }  
package com.zwz.thread.demo2;

public class MainTest {
	public static void main(String[] args) throws InterruptedException {
		ObjectService service=new ObjectService();
		ThreadB b=new ThreadB(service);
		b.start();
		Thread.sleep(2000);
		ThreadA a=new ThreadA(service);
		a.start();
	}
}

运行结果：

可以看到objectMethodA方法异步执行了，下面我们将objectMethodA()加上同步。

[java] view plain copy print?
  1. package com.zwz.thread.demo2;  
  2.   
  3. public class ObjectService {  
  4.     public synchronized void objectMethodA(){  
  5.         System.out.println("run----objectMethodA");  
  6.     }  
  7.     public void objectMethodB(){  
  8.         synchronized (this) {  
  9.             try {  
  10.                 for (int i = 1; i <= 10; i++) {  
  11.                     System.out.println("synchronized thread name:"+Thread.currentThread().getName()+"-->i="+i);  
  12.                     Thread.sleep(1000);  
  13.                 }  
  14.             } catch (InterruptedException e) {  
  15.                     e.printStackTrace();  
  16.             }  
  17.         }  
  18.     }  
  19. }  
package com.zwz.thread.demo2;

public class ObjectService {
	public synchronized void objectMethodA(){
		System.out.println("run----objectMethodA");
	}
	public void objectMethodB(){
		synchronized (this) {
			try {
				for (int i = 1; i <= 10; i++) {
					System.out.println("synchronized thread name:"+Thread.currentThread().getName()+"-->i="+i);
					Thread.sleep(1000);
				}
			} catch (InterruptedException e) {
					e.printStackTrace();
			}
		}
	}
}

运行结果：

结论：

上面三个小例子我们可以知道，多个线程调用同一个对象中的不同名称的synchronized同步方法或synchronized(this)同步代码块时，是同步的。

1、synchronized同步方法

①对其它的synchronized同步方法或synchronized(this)同步代码块调用是堵塞状态；

②同一时间只有一个线程执行synchronized同步方法中的代码。

2、synchronized(this)同步代码块

①对其它的synchronized同步方法或synchronized(this)同步代码块调用是堵塞状态；

②同一时间只有一个线程执行synchronized同步方法中的代码。

将任意对象作为对象监视器

[java] view plain copy print?
  1. package com.zwz.thread.demo3;  
  2.   
  3. public class ObjectService {  
  4.     private String uname;  
  5.     private String pwd;  
  6.     String lock=new String();  
  7.     public void setUserNamePassWord(String userName,String passWord){  
  8.         try {  
  9.             synchronized (lock) {  
  10.                 System.out.println("thread name="+Thread.currentThread().getName()  
  11.                         +" 进入代码快:"+System.currentTimeMillis());  
  12.                 uname=userName;  
  13.                 Thread.sleep(3000);  
  14.                 pwd=passWord;  
  15.                 System.out.println("thread name="+Thread.currentThread().getName()  
  16.                         +" 进入代码快:"+System.currentTimeMillis()+"入参uname:"+uname+"入参pwd:"+pwd);  
  17.             }  
  18.         } catch (InterruptedException e) {  
  19.             e.printStackTrace();  
  20.         }  
  21.     }  
  22. }  
package com.zwz.thread.demo3;

public class ObjectService {
	private String uname;
	private String pwd;
	String lock=new String();
	public void setUserNamePassWord(String userName,String passWord){
		try {
			synchronized (lock) {
				System.out.println("thread name="+Thread.currentThread().getName()
						+" 进入代码快:"+System.currentTimeMillis());
				uname=userName;
				Thread.sleep(3000);
				pwd=passWord;
				System.out.println("thread name="+Thread.currentThread().getName()
						+" 进入代码快:"+System.currentTimeMillis()+"入参uname:"+uname+"入参pwd:"+pwd);
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo3;  
  2.   
  3. public class ThreadA extends Thread {  
  4.     private ObjectService objectService;  
  5.   
  6.     public ThreadA(ObjectService objectService) {  
  7.         super();  
  8.         this.objectService = objectService;  
  9.     }  
  10.     @Override  
  11.     public void run() {  
  12.         objectService.setUserNamePassWord("a", "aa");  
  13.     }  
  14. }  
package com.zwz.thread.demo3;

public class ThreadA extends Thread {
	private ObjectService objectService;

	public ThreadA(ObjectService objectService) {
		super();
		this.objectService = objectService;
	}
	@Override
	public void run() {
		objectService.setUserNamePassWord("a", "aa");
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo3;  
  2.   
  3. public class ThreadB extends Thread {  
  4.     private ObjectService objectService;  
  5.   
  6.     public ThreadB(ObjectService objectService) {  
  7.         super();  
  8.         this.objectService = objectService;  
  9.     }  
  10.     @Override  
  11.     public void run() {  
  12.         objectService.setUserNamePassWord("b", "bb");  
  13.     }  
  14. }  
package com.zwz.thread.demo3;

public class ThreadB extends Thread {
	private ObjectService objectService;

	public ThreadB(ObjectService objectService) {
		super();
		this.objectService = objectService;
	}
	@Override
	public void run() {
		objectService.setUserNamePassWord("b", "bb");
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo3;  
  2.   
  3. public class MainTest {  
  4.     public static void main(String[] args) {  
  5.         ObjectService service=new ObjectService();  
  6.         ThreadA a=new ThreadA(service);  
  7.         a.setName("A");  
  8.         a.start();  
  9.         ThreadB b=new ThreadB(service);  
  10.         b.setName("B");  
  11.         b.start();  
  12.     }  
  13. }  
package com.zwz.thread.demo3;

public class MainTest {
	public static void main(String[] args) {
		ObjectService service=new ObjectService();
		ThreadA a=new ThreadA(service);
		a.setName("A");
		a.start();
		ThreadB b=new ThreadB(service);
		b.setName("B");
		b.start();
	}
}

运行结果：

下面我把String lock=new String();放在方法中会有啥结果了：

[java] view plain copy print?
  1. package com.zwz.thread.demo3;  
  2.   
  3. public class ObjectService {  
  4.     private String uname;  
  5.     private String pwd;  
  6.     public void setUserNamePassWord(String userName,String passWord){  
  7.         try {  
  8.             String lock=new String();  
  9.             synchronized (lock) {  
  10.                 System.out.println("thread name="+Thread.currentThread().getName()  
  11.                         +" 进入代码快:"+System.currentTimeMillis());  
  12.                 uname=userName;  
  13.                 Thread.sleep(3000);  
  14.                 pwd=passWord;  
  15.                 System.out.println("thread name="+Thread.currentThread().getName()  
  16.                         +" 进入代码快:"+System.currentTimeMillis()+"入参uname:"+uname+"入参pwd:"+pwd);  
  17.             }  
  18.         } catch (InterruptedException e) {  
  19.             e.printStackTrace();  
  20.         }  
  21.     }  
  22. }  
package com.zwz.thread.demo3;

public class ObjectService {
	private String uname;
	private String pwd;
	public void setUserNamePassWord(String userName,String passWord){
		try {
			String lock=new String();
			synchronized (lock) {
				System.out.println("thread name="+Thread.currentThread().getName()
						+" 进入代码快:"+System.currentTimeMillis());
				uname=userName;
				Thread.sleep(3000);
				pwd=passWord;
				System.out.println("thread name="+Thread.currentThread().getName()
						+" 进入代码快:"+System.currentTimeMillis()+"入参uname:"+uname+"入参pwd:"+pwd);
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}

运行结果：

结论：

多个线程持有对象监视器作为同一个对象的前提下，同一时间只有一个线程可以执行synchronized(任意自定义对象)同步代码快。

synchronized(任意自定义对象)与synchronized同步方法共用

[java] view plain copy print?
  1. package com.zwz.thread.demo4;  
  2.   
  3. public class ObjectService {  
  4.     private String lock=new String();  
  5.     public void methodA(){  
  6.         try {  
  7.             synchronized (lock) {  
  8.                 System.out.println("a begin");  
  9.                 Thread.sleep(3000);  
  10.                 System.out.println("a   end");  
  11.             }  
  12.         } catch (InterruptedException e) {  
  13.             e.printStackTrace();  
  14.         }  
  15.     }  
  16.     public synchronized void methodB(){  
  17.         System.out.println("b begin");  
  18.         System.out.println("b   end");  
  19.     }  
  20. }  
package com.zwz.thread.demo4;

public class ObjectService {
	private String lock=new String();
	public void methodA(){
		try {
			synchronized (lock) {
				System.out.println("a begin");
				Thread.sleep(3000);
				System.out.println("a   end");
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
	public synchronized void methodB(){
		System.out.println("b begin");
		System.out.println("b   end");
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo4;  
  2.   
  3. public class ThreadA extends Thread {  
  4.     private ObjectService objectService;  
  5.   
  6.     public ThreadA(ObjectService objectService) {  
  7.         super();  
  8.         this.objectService = objectService;  
  9.     }  
  10.     @Override  
  11.     public void run() {  
  12.         objectService.methodA();  
  13.     }  
  14. }  
package com.zwz.thread.demo4;

public class ThreadA extends Thread {
	private ObjectService objectService;

	public ThreadA(ObjectService objectService) {
		super();
		this.objectService = objectService;
	}
	@Override
	public void run() {
		objectService.methodA();
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo4;  
  2.   
  3. public class ThreadB extends Thread {  
  4.     private ObjectService objectService;  
  5.   
  6.     public ThreadB(ObjectService objectService) {  
  7.         super();  
  8.         this.objectService = objectService;  
  9.     }  
  10.     @Override  
  11.     public void run() {  
  12.         objectService.methodB();  
  13.     }  
  14. }  
package com.zwz.thread.demo4;

public class ThreadB extends Thread {
	private ObjectService objectService;

	public ThreadB(ObjectService objectService) {
		super();
		this.objectService = objectService;
	}
	@Override
	public void run() {
		objectService.methodB();
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo4;  
  2.   
  3. public class MainTest {  
  4.     public static void main(String[] args) {  
  5.         ObjectService service=new ObjectService();  
  6.         ThreadA a=new ThreadA(service);  
  7.         a.setName("A");  
  8.         a.start();  
  9.         ThreadB b=new ThreadB(service);  
  10.         b.setName("B");  
  11.         b.start();  
  12.     }  
  13.       
  14. }  
package com.zwz.thread.demo4;

public class MainTest {
	public static void main(String[] args) {
		ObjectService service=new ObjectService();
		ThreadA a=new ThreadA(service);
		a.setName("A");
		a.start();
		ThreadB b=new ThreadB(service);
		b.setName("B");
		b.start();
	}
	
}

运行结果:

结论：

使用synchronized(任意自定义对象)进行同步操作，对象监视器必须是同一个对象。不过不是同一个，运行就是异步执行了。

静态同步synchronized方法与synchronized(*.class)代码块

 

静态同步synchronized方法

[java] view plain copy print?
  1. package com.zwz.thread.demo6;  
  2.   
  3. public class ObjectService {  
  4.     public synchronized static void methodA(){  
  5.         try {  
  6.             System.out.println("static methodA begin 线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());  
  7.             Thread.sleep(3000);  
  8.             System.out.println("static methodA end   线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());  
  9.         } catch (InterruptedException e) {  
  10.             e.printStackTrace();  
  11.         }  
  12.     }  
  13.       
  14.     public synchronized static void methodB(){  
  15.         System.out.println("static methodB begin 线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());  
  16.         System.out.println("static methodB end   线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());  
  17.     }  
  18. }  
package com.zwz.thread.demo6;

public class ObjectService {
	public synchronized static void methodA(){
		try {
			System.out.println("static methodA begin 线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());
			Thread.sleep(3000);
			System.out.println("static methodA end   线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
	
	public synchronized static void methodB(){
		System.out.println("static methodB begin 线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());
		System.out.println("static methodB end   线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo6;  
  2.   
  3. public class ThreadA extends Thread {  
  4.   
  5.     @Override  
  6.     public void run() {  
  7.         ObjectService.methodA();  
  8.     }  
  9. }  
package com.zwz.thread.demo6;

public class ThreadA extends Thread {

	@Override
	public void run() {
		ObjectService.methodA();
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo6;  
  2.   
  3. public class ThreadB extends Thread {  
  4.     @Override  
  5.     public void run() {  
  6.         ObjectService.methodB();  
  7.     }  
  8. }  
package com.zwz.thread.demo6;

public class ThreadB extends Thread {
	@Override
	public void run() {
		ObjectService.methodB();
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo6;  
  2.   
  3. public class MainTest {  
  4.     public static void main(String[] args) {  
  5.         ThreadA a=new ThreadA();  
  6.         a.setName("A");  
  7.         a.start();  
  8.         ThreadB b=new ThreadB();  
  9.         b.setName("B");  
  10.         b.start();  
  11.     }  
  12. }  
package com.zwz.thread.demo6;

public class MainTest {
	public static void main(String[] args) {
		ThreadA a=new ThreadA();
		a.setName("A");
		a.start();
		ThreadB b=new ThreadB();
		b.setName("B");
		b.start();
	}
}
运行结果：
结论：
synchronized应用在static方法上，那是对当前对应的*.Class进行持锁。
 

synchronized(*.class)代码块

[java] view plain copy print?
  1. package com.zwz.thread.demo7;  
  2.   
  3. public class ObjectService {  
  4.     public void methodA(){  
  5.         try {  
  6.             synchronized (ObjectService.class) {  
  7.                 System.out.println("methodA begin 线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());  
  8.                 Thread.sleep(3000);  
  9.                 System.out.println("methodA end   线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());  
  10.             }  
  11.         } catch (InterruptedException e) {  
  12.             e.printStackTrace();  
  13.         }  
  14.     }  
  15.       
  16.     public void methodB(){  
  17.         synchronized (ObjectService.class) {  
  18.             System.out.println("methodB begin 线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());  
  19.             System.out.println("methodB end   线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());  
  20.         }  
  21.     }  
  22. }  
package com.zwz.thread.demo7;

public class ObjectService {
	public void methodA(){
		try {
			synchronized (ObjectService.class) {
				System.out.println("methodA begin 线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());
				Thread.sleep(3000);
				System.out.println("methodA end   线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
	
	public void methodB(){
		synchronized (ObjectService.class) {
			System.out.println("methodB begin 线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());
			System.out.println("methodB end   线程名称:"+Thread.currentThread().getName()+" times:"+System.currentTimeMillis());
		}
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo7;  
  2.   
  3. public class ThreadA extends Thread {  
  4.     private ObjectService objectService;  
  5.   
  6.     public ThreadA(ObjectService objectService) {  
  7.         super();  
  8.         this.objectService = objectService;  
  9.     }  
  10.     @Override  
  11.     public void run() {  
  12.         objectService.methodA();  
  13.     }  
  14. }  
package com.zwz.thread.demo7;

public class ThreadA extends Thread {
	private ObjectService objectService;

	public ThreadA(ObjectService objectService) {
		super();
		this.objectService = objectService;
	}
	@Override
	public void run() {
		objectService.methodA();
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo7;  
  2.   
  3. public class ThreadB extends Thread {  
  4.     private ObjectService objectService;  
  5.   
  6.     public ThreadB(ObjectService objectService) {  
  7.         super();  
  8.         this.objectService = objectService;  
  9.     }  
  10.     @Override  
  11.     public void run() {  
  12.         objectService.methodB();  
  13.     }  
  14. }  
package com.zwz.thread.demo7;

public class ThreadB extends Thread {
	private ObjectService objectService;

	public ThreadB(ObjectService objectService) {
		super();
		this.objectService = objectService;
	}
	@Override
	public void run() {
		objectService.methodB();
	}
}
[java] view plain copy print?
  1. package com.zwz.thread.demo7;  
  2.   
  3. public class MainTest {  
  4.     public static void main(String[] args) {  
  5.         ObjectService service=new ObjectService();  
  6.         ThreadA a=new ThreadA(service);  
  7.         a.setName("A");  
  8.         a.start();  
  9.         ThreadB b=new ThreadB(service);  
  10.         b.setName("B");  
  11.         b.start();  
  12.     }  
  13. }  
package com.zwz.thread.demo7;

public class MainTest {
	public static void main(String[] args) {
		ObjectService service=new ObjectService();
		ThreadA a=new ThreadA(service);
		a.setName("A");
		a.start();
		ThreadB b=new ThreadB(service);
		b.setName("B");
		b.start();
	}
}
运行结果:
上面测试方法是共同对象，下面我们分别实例化一个对象：
[java] view plain copy print?
  1. package com.zwz.thread.demo7;  
  2.   
  3. public class MainTest {  
  4.     public static void main(String[] args) {  
  5.         ObjectService service1=new ObjectService();  
  6.         ObjectService service2=new ObjectService();  
  7.         ThreadA a=new ThreadA(service1);  
  8.         a.setName("A");  
  9.         a.start();  
  10.         ThreadB b=new ThreadB(service2);  
  11.         b.setName("B");  
  12.         b.start();  
  13.     }  
  14. }  
package com.zwz.thread.demo7;

public class MainTest {
	public static void main(String[] args) {
		ObjectService service1=new ObjectService();
		ObjectService service2=new ObjectService();
		ThreadA a=new ThreadA(service1);
		a.setName("A");
		a.start();
		ThreadB b=new ThreadB(service2);
		b.setName("B");
		b.start();
	}
}
运行结果：
结论：
同步synchronized(*.class)代码块的作用其实和synchronized static方法作用一样。Class锁对类的所有对象实例起作用。
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原文地址：https://www.cnblogs.com/firstdream/p/8334154.html