java - Why wait ,notify and notifyAll Methods are in Object Class?

Question

i know that wait() method always written in synchronized method/block and make lock on Object but i want to only know that what problem is arise at that time when this all methods are in Thread class ?

Answer 1

They are also in the Thread class. But a thread instance here is equally well suited as a synchronization object as any other object.

In addition, there have already been voices that question this decision of sun, since now every object carries the burden to be able to be synchronized on, and IMHO they should have refactored this out to separate objects long ago.

If I need to have something to synchronize on, I often do:

private Object syncObject = new Object();

Then I can do my

synchronized(syncObject) 

everywhere in the code and do not have to bother with anyone else accidentially synchronizing on this.