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

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

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());

		}

	}

}

1. package com.zwz.thread.demo1;
2. public class ThreadA extends Thread {
3. private ObjectService objectService;
4. public ThreadA(ObjectService objectService){
5. super();
6. this.objectService=objectService;
7. }
8. @Override
9. public void run() {
10. super.run();
11. objectService.serviceMethodA();
12. }
13. }

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();

	}

}

1. package com.zwz.thread.demo1;
2. public class ThreadB extends Thread {
3. private ObjectService objectService;
4. public ThreadB(ObjectService objectService){
5. super();
6. this.objectService=objectService;
7. }
8. @Override
9. public void run() {
10. super.run();
11. objectService.serviceMethodB();
12. }
13. }

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();

	}

}

1. package com.zwz.thread.demo1;
2. public class MainTest {
3. public static void main(String[] args) {
4. ObjectService service=new ObjectService();
5. ThreadA a=new ThreadA(service);
6. a.setName("a");
7. a.start();
8. ThreadB b=new ThreadB(service);
9. b.setName("b");
10. b.start();
11. }
12. }

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

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

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();

			}

		}

	}

}

1. package com.zwz.thread.demo2;
2. public class ThreadA extends Thread {
3. private ObjectService objectService;
4. public ThreadA(ObjectService objectService) {
5. super();
6. this.objectService = objectService;
7. }
8. @Override
9. public void run() {
10. super.run();
11. objectService.objectMethodA();
12. }
13. }

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();

	}

}

1. package com.zwz.thread.demo2;
2. public class ThreadB extends Thread {
3. private ObjectService objectService;
4. public ThreadB(ObjectService objectService) {
5. super();
6. this.objectService = objectService;
7. }
8. @Override
9. public void run() {
10. super.run();
11. objectService.objectMethodB();
12. }
13. }

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();

	}

}

1. package com.zwz.thread.demo2;
2. public class MainTest {
3. public static void main(String[] args) throws InterruptedException {
4. ObjectService service=new ObjectService();
5. ThreadB b=new ThreadB(service);
6. b.start();
7. Thread.sleep(2000);
8. ThreadA a=new ThreadA(service);
9. a.start();
10. }
11. }

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。

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

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

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

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();

		}

	}

}

1. package com.zwz.thread.demo3;
2. public class ThreadA extends Thread {
3. private ObjectService objectService;
4. public ThreadA(ObjectService objectService) {
5. super();
6. this.objectService = objectService;
7. }
8. @Override
9. public void run() {
10. objectService.setUserNamePassWord("a", "aa");
11. }
12. }

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");

	}

}

1. package com.zwz.thread.demo3;
2. public class ThreadB extends Thread {
3. private ObjectService objectService;
4. public ThreadB(ObjectService objectService) {
5. super();
6. this.objectService = objectService;
7. }
8. @Override
9. public void run() {
10. objectService.setUserNamePassWord("b", "bb");
11. }
12. }

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");

	}

}

1. package com.zwz.thread.demo3;
2. public class MainTest {
3. public static void main(String[] args) {
4. ObjectService service=new ObjectService();
5. ThreadA a=new ThreadA(service);
6. a.setName("A");
7. a.start();
8. ThreadB b=new ThreadB(service);
9. b.setName("B");
10. b.start();
11. }
12. }

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：

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

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

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

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");

	}

}

1. package com.zwz.thread.demo4;
2. public class ThreadA extends Thread {
3. private ObjectService objectService;
4. public ThreadA(ObjectService objectService) {
5. super();
6. this.objectService = objectService;
7. }
8. @Override
9. public void run() {
10. objectService.methodA();
11. }
12. }

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();

	}

}

1. package com.zwz.thread.demo4;
2. public class ThreadB extends Thread {
3. private ObjectService objectService;
4. public ThreadB(ObjectService objectService) {
5. super();
6. this.objectService = objectService;
7. }
8. @Override
9. public void run() {
10. objectService.methodB();
11. }
12. }

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();

	}

}

1. package com.zwz.thread.demo4;
2. public class MainTest {
3. public static void main(String[] args) {
4. ObjectService service=new ObjectService();
5. ThreadA a=new ThreadA(service);
6. a.setName("A");
7. a.start();
8. ThreadB b=new ThreadB(service);
9. b.setName("B");
10. b.start();
11. }
12. }

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

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

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());

	}

}

1. package com.zwz.thread.demo6;
2. public class ThreadA extends Thread {
3. @Override
4. public void run() {
5. ObjectService.methodA();
6. }
7. }

package com.zwz.thread.demo6;

public class ThreadA extends Thread {

	@Override

	public void run() {

		ObjectService.methodA();

	}

}

1. package com.zwz.thread.demo6;
2. public class ThreadB extends Thread {
3. @Override
4. public void run() {
5. ObjectService.methodB();
6. }
7. }

package com.zwz.thread.demo6;

public class ThreadB extends Thread {

	@Override

	public void run() {

		ObjectService.methodB();

	}

}

1. package com.zwz.thread.demo6;
2. public class MainTest {
3. public static void main(String[] args) {
4. ThreadA a=new ThreadA();
5. a.setName("A");
6. a.start();
7. ThreadB b=new ThreadB();
8. b.setName("B");
9. b.start();
10. }
11. }

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

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

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());

		}

	}

}

1. package com.zwz.thread.demo7;
2. public class ThreadA extends Thread {
3. private ObjectService objectService;
4. public ThreadA(ObjectService objectService) {
5. super();
6. this.objectService = objectService;
7. }
8. @Override
9. public void run() {
10. objectService.methodA();
11. }
12. }

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();

	}

}

1. package com.zwz.thread.demo7;
2. public class ThreadB extends Thread {
3. private ObjectService objectService;
4. public ThreadB(ObjectService objectService) {
5. super();
6. this.objectService = objectService;
7. }
8. @Override
9. public void run() {
10. objectService.methodB();
11. }
12. }

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();

	}

}

1. package com.zwz.thread.demo7;
2. public class MainTest {
3. public static void main(String[] args) {
4. ObjectService service=new ObjectService();
5. ThreadA a=new ThreadA(service);
6. a.setName("A");
7. a.start();
8. ThreadB b=new ThreadB(service);
9. b.setName("B");
10. b.start();
11. }
12. }

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：

1. package com.zwz.thread.demo7;
2. public class MainTest {
3. public static void main(String[] args) {
4. ObjectService service1=new ObjectService();
5. ObjectService service2=new ObjectService();
6. ThreadA a=new ThreadA(service1);
7. a.setName("A");
8. a.start();
9. ThreadB b=new ThreadB(service2);
10. b.setName("B");
11. b.start();
12. }
13. }

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。