问一个同步问题

[amdgaming]

当一个线程进入一个对象的一个synchronized方法后，其它线程是否可进入此对象的其它synchronized方法?

[Ant]

不可以 当一个线程进入这个synchronized方法之后，就拥有了这个对象的锁，其他线程进入其他synchronized方法的条件是获得那个锁。但是其他线程可以进入非synchronized方法，因为不需要获得那个锁。

[amdgaming]

貌似 是不可以啊。谢谢楼上的啊

[Fantastic99]

不可以
你用synchronized声明了该方法 如果该方法是非静态的 那么在任何一个实例中
当线程A调用该方法了 那么A就持有了锁了
其他线程再调用该实例中任何修饰了synchronized的方法便会得不到锁 会等待锁的释放
如果该方法是静态的 那么就会到类的级别。

[fatRoach]

方法的synchronized等效于

synchronized(this){
...
}

[sfli_g]

synchronized关键字就是为了处理多线程同步的

[nj_dobetter]

synchronized方法，原理上说是要把对象的数据的存取原子化

[dafeicao]

先占个楼.要不一会找不到 了... 敲测试代码中

[dafeicao]

/**
 * @author Administrator
 * 
 */
public class ThreadTest implements Runnable {

	Test test;

	private int j = 1;

	public Test getTest() {
		return test;
	}

	public void setTest(Test test) {
		this.test = test;
	}

	public ThreadTest(int j) {
		this.j = j;
	}

	public void run() {
		test=Test.getTest();
		test.test1(j);
		test.test2(j);
		test.test3(j);
		test.test4(j);
	}

	public static void main(String[] args) {
		for (int i = 0; i < 10; i++) {
			new Thread(new ThreadTest(i)).start();
		}
		
		
	}
}

class Test {
	private static Test test = null;

	private Test() {
	}

	public static Test getTest() {
		if (test == null) {
			return new Test();
		}
		return test;
	}

	public synchronized void test1(int i) {
		System.out.println("is test1 Thread =" + i);
	}

	public synchronized void test2(int i) {
		System.out.println("is test2 Thread =" + i);
	}

	public synchronized void test3(int i) {
		System.out.println("is test3 Thread =" + i);
	}

	public  void test4(int i) {
		System.out.println("is test4 Thread =" + i);
	}
}

请注意打印出来的is test1 Thread =9 说明其它线程可以进入其它synchronized方法
打印结果:

is test1 Thread =1
is test2 Thread =1
is test3 Thread =1
is test4 Thread =1
is test1 Thread =2
is test2 Thread =2
is test3 Thread =2
is test4 Thread =2
is test1 Thread =0
is test2 Thread =0
is test3 Thread =0
is test4 Thread =0
is test1 Thread =3
is test2 Thread =3
is test3 Thread =3
is test4 Thread =3
is test1 Thread =4
is test2 Thread =4
is test3 Thread =4
is test4 Thread =4
is test1 Thread =6
is test2 Thread =6
is test3 Thread =6
is test4 Thread =6
is test1 Thread =7
is test2 Thread =7
is test3 Thread =7
is test4 Thread =7
is test1 Thread =8
is test2 Thread =8
is test3 Thread =8
is test4 Thread =8
is test1 Thread =9
is test1 Thread =5
is test2 Thread =5
is test3 Thread =5
is test4 Thread =5
is test2 Thread =9
is test3 Thread =9
is test4 Thread =9

[dafeicao]

代码写的有点乱- - 见谅 等 拍

[fatRoach]

“进入其它synchronized方法”的含义你搞明白了么，LS的……

[龙四]

其他进程还能同时进那个方法的话synchronized还有什么意义？！

[feishare]

引用 1 楼 ant_yan 的回复:

不可以 当一个线程进入这个synchronized方法之后，就拥有了这个对象的锁，其他线程进入其他synchronized方法的条件是获得那个锁。但是其他线程可以进入非synchronized方法，因为不需要获得那个锁。

nice

[LuffySY]

引用 8 楼 dafeicao 的回复:

Java code/**
*@author Administrator
**/publicclass ThreadTestimplements Runnable {

Test test;privateint j=1;public Test getTest() {return test;
}publicvoid setTest(Test test) {this.test= test;
}public ThreadTest(int j) {this.j= j;
}publicvoid run() {
test=Test.getTest();
test.test1(j);
test.test2(j);
test.test3(j);
test.test4(j);
}publicstaticvoid main(String[] args) {for (int i=0; i<10; i++) {new Thread(new ThreadTest(i)).start();
}


}
}class Test {privatestatic Test test=null;private Test() {
}publicstatic Test getTest() {if (test==null) {returnnew Test();
}return test;
}publicsynchronizedvoid test1(int i) {
System.out.println("is test1 Thread ="+ i);
}publicsynchronizedvoid test2(int i) {
System.out.println("is test2 Thread ="+ i);
}publicsynchronizedvoid test3(int i) {
System.out.println("is test3 Thread ="+ i);
}publicvoid test4(int i) {
System.out.println("is test4 Thread ="+ i);
}
}


请注意打印出来的is test1 Thread =9    说明其它线程可以进入其它synchronized方法
打印结果:

is test1 Thread =1
is test2 Thread =1
is test3 Thread =1
is test4 Thread =1
is test1 Thread =2
is test2 Thread =2
is test3 Thread =2
is test4 Thread =2
is test1 Thread =0
is test2 Thread =0
is test3 Thread =0
is test4 Thread =0
is test1 Thread =3
is test2 Thread =3
is test3 Thread =3
is test4 Thread =3
is test1 Thread =4
is test2 Thread =4
is test3 Thread =4
is test4 Thread =4
is test1 Thread =6
is test2 Thread =6
is test3 Thread =6
is test4 Thread =6
is test1 Thread =7
is test2 Thread =7
is test3 Thread =7
is test4 Thread =7
is test1 Thread =8
is test2 Thread =8
is test3 Thread =8
is test4 Thread =8
is test1 Thread =9
is test1 Thread =5
is test2 Thread =5
is test3 Thread =5
is test4 Thread =5
is test2 Thread =9
is test3 Thread =9
is test4 Thread =9

那个9打印出来 方法都结束了 没办法证明是进入的。 答案是 不能进入 其他synchronized方法的

[dafeicao]

嗯. 当时欠考虑 可是这种应该写怎样的测试呢?

[nobody165]

dafeicao 貌似你的例子有问题哦。
当一个线程进入一个对象的一个synchronized方法后，其它线程是不可进入此对象的其它synchronized方法的.

[henry_fuzr]

不能 ，synchronized方法的同步锁是this 指的是当前对象。
如果新建一个对象的话就可以