Here is the answer,
Thread.sleep() sends the current thread into the "Not Runnable" state for some amount of time. The thread keeps the monitors it has aquired - i.e. if the thread is currently in a synchronized block or method no other thread can enter this block or method. If another thread calls th.interrupt() it will wake up the sleeping thread.
Note that sleep is a static method, which means that it always affects the current thread (the one that is executing the sleep method). A common mistake is to call th.sleep() where t is a different thread; even then, it is the current thread that will sleep, not the t thread.
object.wait() sends the current thread into the "Not Runnable" state, like sleep(), but with a twist. Wait is called on a object, not a thread; we call this object the "lock object." Before lock.wait() is called, the current thread must synchronize on the lock object; wait() then releases this lock, and adds the thread to the "wait list" associated with the lock. Later, another thread can synchronize on the same lock object and call lock.notify(). This wakes up the original, waiting thread. Basically, wait()/notify() is like sleep()/interrupt(), only the active thread does not need a direct pointer to the sleeping thread, but only to the shared lock object.