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

# ThreadLocal
Consider the following instance method of a class


```java
 void add(int val) {

 int count = 5;
 count += val;
 System.out.println(val);

 }
```

Do you think the above method is thread-safe? If multiple threads call this method, then each executing thread will create a copy of the local variables on its own thread stack. There would be no shared variables amongst the threads and the instance method by itself would be thread-safe.
However, if we moved the <code>count</code> variable out of the method and declared it as an instance variable then the same code will not be thread-safe.
We can have a copy of an instance (or a class) variable for each thread that accesses it by declaring the instance variable ThreadLocal. Look at the thread unsafe code below. If you run it multiple times, you'll see different results. The count variable is incremented 100 times by 100 threads so in a thread-safe world the final value of the variable should come out to be 10,000.

This lesson discusses thread local storage

The Basics

Multithreading in Java

Java's Memory Model

Interview Practice Problems

Bonus Questions

Beyond the Interview

Java Concurrency Reference

Revision & Quizzes

ThreadLocal

ThreadLocal