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>Can you enumerate the implications of the poor design choice for the below class?</p>
<b>

```java
public class BadClassDesign {

    private File file;

    public BadClassDesign() throws InterruptedException {
        Thread t = new Thread(() -> {
            System.out.println(this.file);
        });
        t.start();
        t.join();
    }
}
```
</b>
</div>
    <div class="ans">
        <p>The above class is a bad design choice for the following reasons:</p>

<ul>
<li><p>When creating the thread object in the constructor, the reference to the instance of the enclosing <code class="clazz">BadClassDesign</code> class is also implicitly captured by the anonymous class that implements <code class="intf">Runnable</code>. The problem with this approach is that the anonymous class can attempt to use the enclosing object while it is still being constructed. This would not be an issue if we didn't start the thread in the constructor. Note that if we invoked an overrideable instance method in the constructor, we'll be giving a derived class a chance to access the half constructed object in an unsafe manner.</p></li>
<li><p>The private fields of the <code class="clazz">BadClassDesign</code> class also become accessible to the instance of the anonymous inner class that we pass in to the <code class="clazz">Thread</code> class's constructor.</p></li>
</ul>


</div>
</div>


<div>
   # Question # 1
    <div>
        <p>Can you enumerate the implications of the poor design choice for the below class?</p>
<b>

```java
public class BadClassDesign {

    private File file;

    public BadClassDesign() throws InterruptedException {
        Thread t = new Thread(() -> {
            System.out.println(this.file);
        });
        t.start();
        t.join();
    }
}
```
</b>
</div>
    <div>
        <p>The above class is a bad design choice for the following reasons:</p>

<ul>
<li><p>When creating the thread object in the constructor, the reference to the instance of the enclosing <code>BadClassDesign</code> class is also implicitly captured by the anonymous class that implements <code>Runnable</code>. The problem with this approach is that the anonymous class can attempt to use the enclosing object while it is still being constructed. This would not be an issue if we didn't start the thread in the constructor. Note that if we invoked an overrideable instance method in the constructor, we'll be giving a derived class a chance to access the half constructed object in an unsafe manner.</p></li>
<li><p>The private fields of the <code>BadClassDesign</code> class also become accessible to the instance of the anonymous inner class that we pass in to the <code>Thread</code> class's constructor.</p></li>
</ul>


</div>
</div>


Threaded design and thread-safety questions.

The Basics

Multithreading in Java

Java's Memory Model

Interview Practice Problems

Bonus Questions

Beyond the Interview

Java Concurrency Reference

Revision & Quizzes

Quiz 7

Question # 1