One of the common interview question is “What is difference between sleep and wait in java”.Before we actually see differences,let me give you brief introduction of both.
sleep
- It causes current executing thread to sleep for specific amount of time.
- Its accuracy depends on system timers and schedulers.
- It keeps the monitors it has acquired, so if it is called from synchronized context, no other thread can enter that block or method.
- If we call interrupt() method , it will wake up the sleeping thread.
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synchronized(lockedObject) { Thread.sleep(1000); // It does not release the lock on lockedObject. // So either after 1000 miliseconds, current thread will wake up, or after we call //t. interrupt() method. } |
wait
- It causes current thread to wait until either another thread invokes the notify() method or the notifyAll() method for this object
- It must be called from synchronized context i.e. from block or method.It means before wait() method is called,current thread must have lock on that object.
- It releases lock on the object on which it is called and added to wait list, so another thread can acquire lock on the object.
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synchronized(lockedObject) { lockedObject.wait(); // It releases the lock on lockedObject. // So until we call notify() or notifyAll() from other thread,It will // not wake up } |
sleep vs wait:
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Parameter
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wait
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sleep
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Synchonized
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wait should be called from synchronized context i.e. from block or method, If you do not call it using synchronized context, it will throw IllegalMonitorStateException |
It need not be called from synchronized block or methods
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Calls on
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wait method operates on Object and defined in Object class |
Sleep method operates on current thread and is in java.lang.Thread
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Release of lock
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wait release lock of object on which it is called and also other locks if it holds any
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Sleep method does not release lock at all
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Wake up condition
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until call notify() or notifyAll() from Object class
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Until time expires or calls interrupt()
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static
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wait is non static method
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sleep is static method
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You can go through core java interview questions for beginners and experienced for more such questions.
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