Introduction to Thinking in Java objects (1)

Alan Kay summarizes the five basic features of Smalltalk (one of the languages on which Java is based):

① All things are objects

Consider an object as a fancy variable that can store data and perform operations on itself.

② programs are collections of objects that tell each other what they want to do by sending messages.

You can resemble a message as a call request to a method on a particular object.

③ each object has its own storage that is composed of other objects.

In other words, you can create a new type of object by creating a package that contains an existing object.

④ Each object has its type.

Each object is an instance of a class (instance).

⑤ all objects of a particular type can receive the same message.

Booch a more concise description of the object: The object is a friend state (internal data), a behavior (method), and an identity (a unique address in memory).

Introduction to Thinking in Java objects (1)