what is the difference between sleep() and Wait()?

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
t.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
t.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.



thread.sleep(2000) - this will block the thread exactly 2000
milliseconds.

thread.wait(2000) - this will block the thread upto 2000
milliseconds.

i.e if thread.notify() calls before 2000 milliseconds, the
thread will become active incase if the thread is blocked by
wait().