同步方法和锁

Question

当线程调用同步方法时，它会自动获取该方法对象的内在锁，并在该方法返回时释放该内在锁，但是当调用静态同步方法时会发生什么，因为静态方法与类而非对象相关联？

Answer 1

A class is an Object too. When invoking synchronized static method, you acquire a lock on Class object.

Answer 2

Every classes and interface in java has an associated object.

For a class name MyClass, you can get the class object by

MyClass.class

From any object obj, you can get the class object by

obj.getClass()

The lock is obtained for this object when a static method is synchronized.

Answer 3

Just to make it clear- that still means, for example, one thread executes a synchronized nonstatic method, while the other does synchronized static method. You just cannot have two threads execute 2 synchronized static methods at the same time.