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Head First Java Chapter 02

This is the second Chapter learning of Head First Java by Kathy Sierra and Bert Bates, This markdown file is my notes for the second chapter, not sure if any copyright issues are there.

Procedural Programmer (PP) vs Object Oriented Programmer(OOP)

  • PP thinks in terms of what things this program has to do, but OOP thinks what are the things in the program.
  • When Specification of program change the PP have to change the existing code and re-test all, but for OOP, he has test only the changed portion.
  • In OO programming, you can always follow these steps for efficient design
  • Check what is common in all the classes.
  • Abstract the common feature and put in a super class.
  • Inherit all the Sub Class with feature from Super class.
  • Override any specific requirement in one of the Sub Class.

Bullet Point

  • Object-Oriented programming lets you extend a program without having to touch previously-tested, working code.
  • All java code is defined in a class.
  • A class describes how to make an object of that class type. A Class is like a blueprint.
  • An object can take care of itself, you don't have to know or care how the object does it.
  • An object knows things and does things.
  • Things an object knows about itself are called instance variables. They represent the state of an object.
  • Things an object does are called methods. They represent the behavior of an object.
  • When you create a class, you may also want to create a separate test class which you will use to create objects of your class type.
  • A class can inherit instance variables and method from a more abstract superclass.
  • At runtime, a java program is nothing more than objects 'talking' to other object.