Java II Course Study Notes: OOP Concept

Java OOP Concept

General Info

Object-Oriented Programming
Encapsulation
Polymorphism
Inheritance
Abstraction
Class and object
Pass by value
this() vs. super

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Object-Oriented Programming

An extension of procedural programming.
Component like, reusability, secure and quick development.
Everything in a class.
An class == an object == an application.
Procedural programming vs. object oriented programming

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Encapsulation

benefits: hide details, better maintainable, access control.
private
non-access modifier
protected
public

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Polymorphism

Many different forms.
An object has only one form
A reference variable has many forms
Overload: same method name, different arguments, return type flexible.
Override: same method name, same arguments, same return type, but in a subclass. same type exception and no less accessible.
Passing variables

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Inheritance

is-a relationship
extends one super class
implements more interfaces
abstract
single vs. multiple inheritance
this vs. super

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Abstraction

An abstract class with a single inheritance
An interface with multiple inheritance.
Abstract vs. interface.
Why using interface instead of abstract class.

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Classes and Objects

class: template or model
object: created based on that model
One program one class, but may have many objects by using new keyword.

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Pass by value

Only passes arguments by value
An object instance is passed to a method, the value of the argument is a reference to the object.
The contents of the object may be changed but the object reference is never changed.

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this() vs. super()

this() calls the enclosing class constructor.
super() calls the super class constructor.
this.member indicates the enclosing class's element.
super.method() calls super methods
Either this() or super() should be the first statement in a block.

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