This tutorial will directly build on concepts and source code from my Creating a Thread Part One Tutorial and Creating a Thread Part Two Tutorial. In this tutorial I will demonstrate how to create multiple child threads using both versions of my custom prime-number-calculating class. I will also introduce you to a concept called thread safety. A method in Java is considered to be thread safe if it can be used by multiple threads without causing any problems. You will see how easy it is to get wrapped up in the power of multithreading without considering the side-effects of thread safety.