Eclipse Auto-Compile

Automatic compilation:
There is no point in Java applications, and for Web applications, when you modify the code, it automatically compiles and publishes it to the Web container, saving you from restarting the Web container.

Build: Compile, the compilation of Eclipse is based on the judging mechanism of timestamp.
Clean: When you click Build all, some eclipse thinks the class with the timestamp unchanged will not be compiled, so it needs to be clean and then compiled. option will delete the. class file in the project and recompile the project.

Set up:
Project→build automatically

Eclipse Auto-Compile