In Java, both sleep() and wait() methods are used to pause the execution of a thread, but they serve different purposes and are used in different contexts.
sleep() Method:
Class Belonging: sleep() is a static method of the Thread class.
Purpose: It is used to pause the execution of the current thread for a specified duration of time.
Lock Behavior: When a thread is put to sleep, it holds any locks it has – it does not release any object locks.
Usage Context: sleep() can be called from any context and is not dependent on the object's monitor.
Method Signature: sleep() has two overloaded versions: sleep(long millis) and sleep(long millis, int nanos), both of which can throw InterruptedException.
Interruption: If another thread interrupts the sleeping thread, it throws an InterruptedException.
Static Method: Being a static method, sleep() always affects the current executing thread, regardless of which thread object calls it.
wait() Method:
Class Belonging: wait() is a non-static method and is part of the Object class.
Purpose: It causes the current thread to wait until another thread invokes notify() or notifyAll() on the same object or until the optional timeout expires.
Lock Behavior: When wait() is invoked, the calling thread releases the lock on the object to allow other threads to synchronize on that object.
Usage Context: wait() must be called from a synchronized context – the calling thread must own the object's monitor.
Method Signature: wait() has three versions: wait(), wait(long timeout), and wait(long timeout, int nanos), all of which can throw InterruptedException.
Interruption: A thread in wait() state can be woken up before the notify call or timeout by an InterruptedException.
Object Lock: wait() is always about the object lock; when a thread calls wait(), it sets itself in a wait state on that object's monitor.
Key Differences:
Lock Release: wait() releases the monitor lock, sleep() does not.
Class Membership: wait() is in Object class, sleep() is ...
