Java Multithreading Interview Questions

Multithreading is the ability to execute multiple threads or tasks concurrently on a single platform. In Java, Multithreading has emerged as one of the important elements as it allows a user to perform several tasks in single code or thread. When it comes to asking questions related to multithreading in Java, an interviewer should focus on several key points as listed below:

• Multithreading:

The very first insight an interviewer must seek in the candidate is about Multithreading itself, that the candidate has a basic knowledge about the concept and he/she can deliver a proper definition of the subject. The question may become, 'What is Multithreading?' or 'What is a thread?' The answer to which is, 'Multithreading is the process of executing multiple threads simultaneously.'

• Advantages of Multithreading:

Next, an interviewer can ask about the advantages that are bestowed upon with this technique, it will give even a deeper insight on the knowledge of the candidate. The answer to which is that 'Threads share a common address space, they are lightweight and the cost of communication between the process is low.'

• The difference between preemptive scheduling and time slicing:

Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.

• Join() Method:

The join() method waits for a thread to die. In other words, it causes the currently running threads to stop executing until the thread it joins with completes its task.

• Shutdown Hook:

The shutdown hook is basically a thread i.e. invoked implicitly before JVM shuts down. So we can use it perform clean up the resource.

• Synchronization:

Synchronization is the capability of control the access of multiple threads to any shared resource. It is used:
√ To prevent thread interference.
√ To prevent consistency problem.

• Static Synchronization:

If you make any static method as synchronized, the lock will be on the class not on the object. The synchronized element will thus be automatically inherited by all the members of the class and there is no need to add an object from outside.
There are several other concepts in Multithreading in Java which could be used to ask about in an interview such as process based multitasking, thread based multitasking, a life cycle of a thread, thread scheduler etc. but the core knowledge about the points mentioned above is enough to check a candidate's knowledge.

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