An abstract class is a template definition of methods and variables in a specific class, or category of objects. In programming, objects are units of code, and each object is made into a generic class ...

Remember that an interface is a kind of contract that must be implemented by a concrete class. Interface methods are implicitly abstract, and also require a concrete class implementation.

Use only one level of indentation per method. If you need more than one level ... If you want to use an integer, you first have to create a class (even an inner class) to identify it’s true ...