Java中同步时的方法可访问性

Question

Suppose there are four methods(m1, m2, m3, m4) and two threads(t1, t2) , now I want to know below-

1. Non-static case:

a) Suppose all methods are synchronized but non-static and say t1 is accessing m1, then can t2 access m2/m3/m4 ?

b) Suppose m1 & m2 are synchronized and m3 & m4 are non-synchronized , all are non-static , now say t1 is accessing m1, then can t2 access m2/m3/m4 ?

2. Static case:

a) Suppose all methods are synchronized & static and say t1 is accessing m1, then can t2 access m2/m3/m4 ?

b) Suppose all methods are static and m1 & m2 are synchronized and m3 & m4 are non-synchronized , now say t1 is accessing m1, then can t2 access m2/m3/m4 ?

3. Mixed Case:

a) m1&m2- static & synchronized , m3&m4- non-static & non-synchronized . Now say t1 is accessing m1, then can t2 access m2/m3/m4 ?

b) m1- static & synchronized , m2- static & non-synchronized , m3- non-static & synchronized , m4- non-static & non-synchronized . Now say t1 is accessing m1, then can t2 access m2/m3/m4 ?

Can someone please answer and explain on above ? Thanks !

Answer 1

1.
a) No.
b) Only m3 and m4 .
2.
a) No.
b) Only m3 and m4 .
3.
a) Only m3 and m4 .
b) Yes.

Answer 2

According to the JLS :

A synchronized statement acquires a mutual-exclusion lock on behalf of the executing thread, executes a block, then releases the lock. While the executing thread owns the lock, no other thread may acquire the lock.

In the case of a synchronized non static method the lock is acquired on the monitor associated with the instance the method was invoked on.

In the case of a synchronized static method the lock is acquired on the monitor associated with the Class object of the class in which the called method is defined.

See the Synchronization section in the JLS.