static synchronized and non static synchronized methods in threads

Question

can any one explain the statement ..."static synchronized method and non static synchronized method will not block each other -they can run at the same time"

Answer 1

static synchronized void test() { foo(); }

equals

static void test() { synchronized(MyClass.class) { foo(); } }

while

synchronized void test() { foo(); }

equals

void test() { synchronized(this) { foo(); } }

This means: static methods lock on the class object of the class. Non-static methods lock on the instance on which they're called (by default, synchronized(anyOtherLock) is also possible). Since they lock on different objects, they don't block each other.

Answer 2

The lock objects are different on the static method and non-static method. The static method uses the Class object as the lock (lock obj: MyClass.class), while the non-static method uses the instance object as the lock to which the invocation of the method at that time is bound (lock obj: this).