Thread. sleep() takes the current thread to a "Not Runnable" state for specified amount of time. The thread holds the monitors it has acquired. For example, if a thread is running a synchronized block or method and sleep method is called then no other thread will be able to enter this block or method. The sleeping thread can wake up when some other thread calls t. interrupt on it. Note that sleep is a static method, that means it always affects the current thread (the one executing sleep method).