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 are some of the differences between a process and a thread?</p>
    </div>
    <div class="ans">
      <ul>
<li><p>A process can have many threads, whereas a thread can belong to only one process.</p></li>
<li><p>A thread is lightweight than a process and uses less resources than a process.</p></li>
<li><p>A thread has some state private to itself but threads of a process can share the resources allocated to the process including memory address space.</p></li>
</ul>
</div>
</div>

<div class="card">
   # Question # 2
    <div class="qtn">
        <p>Given the below code, can you identify what the coder missed?</p>

```java
    void defectiveCode(final int n) throws ExecutionException, InterruptedException {

        ExecutorService threadPool = Executors.newFixedThreadPool(5);

        Callable<Void> sumTask = new Callable<Void>() {

            public Void call() throws Exception {
                System.out.println("Running");
                return null;
            }
        };

        threadPool.submit(sumTask);
        f.get();
    }
```
</div>

<div class="ans">
<p>The above code forgets to <b><i>shutdown</i></b> the executor thread pool. The thread pool when instantiated would also create 5 worker threads. If we don't shutdown the executor when exiting the main method, then JVM would also not exit. It will keep waiting for the pool's worker threads to finish, since they aren't marked as daemon. As an example execute the below code snippet.</p>
</div>

<div>
   # Question # 1
    <div>
        <p>What are some of the differences between a process and a thread?</p>
    </div>
    <div>
      <ul>
<li><p>A process can have many threads, whereas a thread can belong to only one process.</p></li>
<li><p>A thread is lightweight than a process and uses less resources than a process.</p></li>
<li><p>A thread has some state private to itself but threads of a process can share the resources allocated to the process including memory address space.</p></li>
</ul>
</div>
</div>

<div>
   # Question # 2
    <div>
        <p>Given the below code, can you identify what the coder missed?</p>

```java
    void defectiveCode(final int n) throws ExecutionException, InterruptedException {

        ExecutorService threadPool = Executors.newFixedThreadPool(5);

        Callable<Void> sumTask = new Callable<Void>() {

            public Void call() throws Exception {
                System.out.println("Running");
                return null;
            }
        };

        threadPool.submit(sumTask);
        f.get();
    }
```
</div>

<div>
<p>The above code forgets to <b><i>shutdown</i></b> the executor thread pool. The thread pool when instantiated would also create 5 worker threads. If we don't shutdown the executor when exiting the main method, then JVM would also not exit. It will keep waiting for the pool's worker threads to finish, since they aren't marked as daemon. As an example execute the below code snippet.</p>
</div>

The Basics

Multithreading in Java

Java's Memory Model

Interview Practice Problems

Bonus Questions

Beyond the Interview

Java Concurrency Reference

Revision & Quizzes

Quiz 1

Question # 1

Question # 2