When we develop software, we need to write code. Our code consists of packages with classes, and those can be dependent on the other classes and packages in our project. This is fine for one project, but we sometimes depend on classes in other projects we didn't develop ourselves, for example, we might want to use classes from an Apache Commons library or we might be working on a project that is part of a bigger, multi-project application and we are dependent on classes in these other projects.

Most of the time, when we write software, we want to use classes outside of our project. Actually, we have a dependency on those classes. Those dependent classes are mostly stored in archive files, such as Java Archive (JAR) files. Such archive files are identified by a unique version number, so we can have a dependency on the library with a specific version.

In this chapter, you are going to learn how to define dependencies in your Gradle project. We will see how we can define the configurations of dependencies. You will learn about the different dependency types in Gradle and how to use them when you configure your build.