I want to be an open source contributor. I'm thinking about cloning a project and playing with the files. But how can I compile those files? Since there are so many files, should I compile them one by one with a long classpath list, or there are some convenient way to compile them together?
Usually such an open source project uses some build systems; for example, the "Apache Maven". In this situation, after cloning the project, you just run the build command in the root of the project, like mvn compile for compiling the project.
For more information about some java build systems, refer to this tutorial which talks about "Maven" and also "Gradle" as two common build system in Java world:
https://technologyconversations.com/2014/06/18/build-tools/