OOP

Object oriented programming

is a method of implementation in which programs are organized as cooperative collections of objects, each of which represents an instance of some class, and whose classes are all members of one or more hierarchy of classes united via inheritance relationships.

Class

Definition of objects that share structure, properties, and behaviors

Instance

Concrete object, created from a certain class

Write Once Run Anywhere

WORA meaning

Methods

used to describe behavior of the objects of a class

Methods

is a set of statements which is referred to by name and can be invoked at any point, in a program. it performs a logical unit of work.

Return type

it indicates the data type of the variable returned by a method

Constructors

is a block of code defined in a class that initializes the newly created object

Constructors

It is structurally very similar to an instance method, but it doesn't have a return type.

Constructors

It is automatically called when the instance of a class is created.

Default Constructors

If a class does not have any constructors

No Argument Constructors

is one that takes no parameters

Parameterized Constructors

a constructor with arguments or parameters

Encapsulation

is the mechanism that binds together code and the data it manipulates, and keeps both safe from outside interference and misuse.

Abstraction

is a process of hiding the implementation details from the user, only the functionality will be provided to the user. In other words, the user will have the information on what the object does instead of how it does

Java

Abstraction is achieved using Abstract classes and interfaces.

Abstract class

is a class that is declared with abstract keyword.

Abstract method

is a method that is declared without an implementation.

Subclass

A method defined abstract must always be redefined in the _______

Inheritance

is the process by which one object acquires the properties of another object.

Subclass

A class that is derived from another class

Super class

The class from which the subclass is derived

Polymorphisms

it means the ability to request that the same methods be performed by a wide range of different types of things.

many forms

Polymorphism comes from Greek word

Members

are the variables and the methods declared in the class

Variable Scope

The member of a class are the variables and the methods declared in the class

This & Super

It refers to the variables and methods of the current class instance.

This & Super

It can also be used to refer to the constructor of the class

Dot operator

A member method can be invoked by joining the class name and the method signature with a _________

Instance Variables

When a member variable or a field is declared within a class definition, every object instantiated from that class contains its own copy of it

Class Variables

There are also cases when all instances of a class share a variable

Static

Such class variables are defined with the keyword

Instance methods

are methods within Java class definition without the use of the static keyword

Class methods

are methods within Java class definition with the use of the static keyword

Access Modifiers

used to set the visibility and accessibility of class, methods or variable

Access control

other way to enforce encapsulation

Public, Private, Protected, Default

Ex. Of Access Modifier

Public

can be access by all

Private

can only access within class

Protected

can only accessed by the class, subclass and classes from the same package

Default

no access modifier declared.