Differences between wait() and join() methods in Java

The wait() and join() methods are used to pause the current thread. The wait() is used in with notify() and notifyAll() methods, but join() is used in Java to wait until one thread finishes its execution. wait() is mainly used for shared resources, a thread notifies other waiting thread when a resource becomes free. On the other hand join() is used for waiting a thread to die.

Similarities between wait() and join()

• The method wait() and join() both are used to pause the current thread in Java.
• Both wait() and join() can be interrupted by calling interrupt() method in Java.
• Both wait() and join() are a non-static method.
• Both wait() and join() are overloaded in Java. wait() and join() which without timeout as well as accepts a timeout parameter.

Difference between wait() and join() method

• Most obvious difference, both are present different packages, the wait() method is declared in java.lang.Object class while join() is declared in java.lang.Thread class.
• The wait() is used for inter-thread communication while the join() is used for adding sequencing between multiple threads, one thread starts execution after first thread execution finished.
• We can start a waiting thread (went into this state by calling wait()) by using notify() and notifyAll() method but we can not break the waiting imposed by join without unless or interruption the thread on which join is called has execution finished.
• One most important difference between wait() and join() that is wait() must be called from synchronized context i.e. synchronized block or method otherwise it will throw IllegalMonitorStateException but On the other hand, we can call join() method with and without synchronized context in Java.

Let us understand the differences in a tabular form -:

wait()	join()
It is a method of java.lang.Object class.	It is a method of java.lang.
wait() method can be called by a synchronized block or method.	It is used to stop the current thread.
wait() method is implemented for performing multi-thread-synchronization.	It can be called either with synchronized and without synchronized context.
Its syntax is -: public final void wait() throws InterruptedException	Its syntax is -: public final void join() throws InterruptedException
wait() method causes the thread to sleep until notify() and notifyAll() are called	It can be used to add sequence among more than one thread