Anonymous classes : Java

An anonymous class is pretty much just a way to extend a class or implement an interface without having to create a whole new class.

Use them if you need to use a local class only once.

The syntax of an anonymous class expression is like the invocation of a constructor, except that there is a class definition contained in a block of code.

JavaDocs: https://docs.oracle.com/javase/tutorial/java/javaOO/anonymousclasses.html