The only guide you’ll need on concurrency & multithreading for senior engineers. Pressure test your skills with real-world practice problems from top companies.

Concurrency in Java is one of the most complex and advanced topics brought up during senior engineering interviews. Knowledge of concurrency and multithreading can put interviewees at a considerable advantage. This course lays the foundations of advanced concurrency and multithreading and explains concepts such as Monitors and Deferred Callbacks in depth. It also builds simple and complete solutions to popular concurrency problems that can be asked about in interviews like the Reader-Writer Problem and the Dining Philosopher Problem. While prior knowledge of concurrency is not required to follow through with this course, familiarity with the very basics of concurrency would be helpful.

Java Multithreading for Senior Engineering Interviews

<div class="card">
   # Question # 1
    <div class="qtn">
        <p>What is a thread safe class?</p>
    </div>
    <div class="ans">
        <p><span class="hi-yl">A class is thread safe if it behaves correctly when accessed from multiple threads, irrespective of the scheduling or the interleaving of the execution of those threads by the runtime environment</span>, and with no additional synchronization or other coordination on the part of the calling code.</p>
</div>
</div>


<div class="card-quiz">
   # Question # 2
    <div class="qtn">
        <p>Is the following class thread-safe?</p>

```java
public class Sum {

    int sum(int... vals) {

        int total = 0;
        for (int i = 0; i < vals.length; i++) {
            total += vals[i];
        }
        return total;
    }
}
```
</div>
</div>



<div class="ans">
# Show Explanation
<div style="display:nonee"><p class="exp">The class <code class="clazz">Sum</code> is stateless i.e. it doesn't have any member variables. <span class="hi-yl">All stateless objects and their corresponding classes are thread-safe. Since the actions of a thread accessing a stateless object can't affect the correctness of operations in other threads, stateless objects are thread-safe.</span></p>
<p><b><span class="hi-yl">However, note that the method takes in variable arguments and the class wouldn't be thread safe anymore if the passed in argument was an array instead of individual integer variables and at the same the time, the <code class="mthd">sum</code> method performed a write operation on the passed in array.</p>
</div>
</div>


<div>
   # Question # 1
    <div>
        <p>What is a thread safe class?</p>
    </div>
    <div>
        <p><span>A class is thread safe if it behaves correctly when accessed from multiple threads, irrespective of the scheduling or the interleaving of the execution of those threads by the runtime environment</span>, and with no additional synchronization or other coordination on the part of the calling code.</p>
</div>
</div>


<div>
   # Question # 2
    <div>
        <p>Is the following class thread-safe?</p>

```java
public class Sum {

    int sum(int... vals) {

        int total = 0;
        for (int i = 0; i < vals.length; i++) {
            total += vals[i];
        }
        return total;
    }
}
```
</div>
</div>



<div>
# Show Explanation
<div><p>The class <code>Sum</code> is stateless i.e. it doesn't have any member variables. <span>All stateless objects and their corresponding classes are thread-safe. Since the actions of a thread accessing a stateless object can't affect the correctness of operations in other threads, stateless objects are thread-safe.</span></p>
<p><b><span>However, note that the method takes in variable arguments and the class wouldn't be thread safe anymore if the passed in argument was an array instead of individual integer variables and at the same the time, the <code>sum</code> method performed a write operation on the passed in array.</p>
</div>
</div>


Questions on thread-safety and race conditions

The Basics

Multithreading in Java

Java's Memory Model

Interview Practice Problems

Bonus Questions

Beyond the Interview

Java Concurrency Reference

Revision & Quizzes

Quiz 2

Question # 1

Question # 2