Execution threads are the core of concurrent applications. When you implement a concurrent application, no matter the language, you have to create different execution threads that run in parallel in a non-deterministic order unless you use a synchronization element (such as a semaphore). In Java you can create execution threads in two ways:

• Extending the Thread class
• Implementing the Runnable interface

In this chapter, you will learn how to use these elements to implement concurrent applications in Java. We will cover the following topics:

• Threads in Java: characteristics and states
• The Thread class and the Runnable interface
• First example: matrix multiplication
• Second example: file search