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

## wait()

The <code>wait</code> method is exposed on each java object. Each Java object can act as a condition variable. When a thread executes the <code>wait</code> method, it releases the monitor for the object and is placed in the wait queue. Note that the thread must be inside a synchronized block of code that synchronizes on the same object as the one on which wait() is being called, or in other words, the thread must hold the monitor of the object on which it'll call wait. If not so, an illegalMonitor exception is raised!

# notify()
Like the wait method, <code>notify()</code> can only be called by the thread which owns the monitor for the object on which <code>notify()</code> is being called else an illegal monitor exception is thrown. The notify method, will awaken one of the threads in the associated wait queue, i.e., waiting on the thread's monitor.

However, this thread will not be scheduled for execution immediately and will compete with other active threads that are trying to synchronize on the same object. The thread which executed notify will also need to give up the object's monitor, before any one of the competing threads can acquire the monitor and proceed forward.

# notifyAll()
This method is the same as the <code>notify()</code> one except that it wakes up all the threads that are waiting on the object's monitor.

## wait()

The <code>wait</code> method is exposed on each java object. Each Java object can act as a condition variable. When a thread executes the <code>wait</code> method, it releases the monitor for the object and is placed in the wait queue. Note that the thread must be inside a synchronized block of code that synchronizes on the same object as the one on which wait() is being called, or in other words, the thread must hold the monitor of the object on which it'll call wait. If not so, an illegalMonitor exception is raised!

# notify()
Like the wait method, <code>notify()</code> can only be called by the thread which owns the monitor for the object on which <code>notify()</code> is being called else an illegal monitor exception is thrown. The notify method, will awaken one of the threads in the associated wait queue, i.e., waiting on the thread's monitor.

However, this thread will not be scheduled for execution immediately and will compete with other active threads that are trying to synchronize on the same object. The thread which executed notify will also need to give up the object's monitor, before any one of the competing threads can acquire the monitor and proceed forward.

# notifyAll()
This method is the same as the <code>notify()</code> one except that it wakes up all the threads that are waiting on the object's monitor.

The Basics

Multithreading in Java

Java's Memory Model

Interview Practice Problems

Bonus Questions

Beyond the Interview

Java Concurrency Reference

Revision & Quizzes

Wait & Notify