Classes, fields, methods, constructors, and objects are the building blocks of object-based Java applications ... You don’t have to create any Book objects to call class methods.

Classes and objects in Java must be initialized before they are ... developers resort to performance tricks such as creating and initializing arrays of sines and cosines. Combining class field ...

Classes in higher layers can extend or wrap classes in lower ... as it may result in very subtle bugs. Object slicing throws away information. But in some situations this may be exactly what we want.