The ultimate guide to Java interviews with 300+ real-world questions and answers. Get interview-ready in just a few hours with strategies developed by FAANG engineers.

It’s very common to have interviews testing your knowledge of a programming language you claim to be an expert in.

If you've got an interview coming up on Java soon and need to get up to speed, this is the ideal course for you. You'll refresh your memory on everything from the basics to more advanced functionality you’re likely to be asked about. Even if you're using Java every day, you may not have been exposed to parts of it in some time, so it's always useful to make sure you're updated.

This course features more than 300 of the most commonly asked core Java interview questions that you're likely to face as an experienced software engineer. You'll get to explore questions by topic, as well as see detailed answers for each one, and plenty of live code examples where relevant. Get started today.

The Java Interview Handbook: 300+ Interview Questions

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   # Question # 1
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        <p>What is the difference between a mutex and a semaphore?</p>
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    <div class="ans">
        <p><Mutex as the name hints, implies mutual exclusion. A mutex is used to guard shared data such as a linked-list, an array or any primitive type. <span class="hi-yl">A mutex allows only a single thread to access a resource. It forces competing threads to serialize their access for the requested resource.</span></p>
<p>Semaphore, on the other hand, is used for limiting access to a collection of resources. <span class="hi-yl">Think of semaphore as having a limited number of permits to give out. If a semaphore has given out all the permits it has, then any new thread that comes along requesting for a permit will be blocked, till an earlier thread with a permit returns it to the semaphore.</span> A typical example would be a pool of database connections that can be handed out to requesting threads. Say there are ten available connections but 50 requesting threads. In such a scenario, a semaphore can only give out ten permits or connections at any given point in time.</p>
<p>A semaphore with a single permit is called a binary semaphore and is often thought of as an equal of a mutex, which isn't completely correct. <span class="hi-yl">Semaphores can also be used for signalling among threads.</span> This is an important distinction as it allows threads to cooperatively work towards completing a task. A mutex, on the other hand, is strictly limited to serializing access to shared state among competing threads.</p>
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<div>
   # Question # 1
    <div>
        <p>What is the difference between a mutex and a semaphore?</p>
    </div>
    <div>
        <p><Mutex as the name hints, implies mutual exclusion. A mutex is used to guard shared data such as a linked-list, an array or any primitive type. <span>A mutex allows only a single thread to access a resource. It forces competing threads to serialize their access for the requested resource.</span></p>
<p>Semaphore, on the other hand, is used for limiting access to a collection of resources. <span>Think of semaphore as having a limited number of permits to give out. If a semaphore has given out all the permits it has, then any new thread that comes along requesting for a permit will be blocked, till an earlier thread with a permit returns it to the semaphore.</span> A typical example would be a pool of database connections that can be handed out to requesting threads. Say there are ten available connections but 50 requesting threads. In such a scenario, a semaphore can only give out ten permits or connections at any given point in time.</p>
<p>A semaphore with a single permit is called a binary semaphore and is often thought of as an equal of a mutex, which isn't completely correct. <span>Semaphores can also be used for signalling among threads.</span> This is an important distinction as it allows threads to cooperatively work towards completing a task. A mutex, on the other hand, is strictly limited to serializing access to shared state among competing threads.</p>
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This lesson explains the difference between mutexes and semaphores.

Java Ecosystem

Methods

Classes

Interfaces

Inheritance

Lambda Expressions

Generics

Multi-Threading

Memory Management

Collections

Exceptions

Reflection

Serialization

Miscellaneous Topics

Java in Practice

Patterns

The End

Mutexes vs Semaphores

Question # 1