OOPS

Object Oriented Programming System

Organizes code into objects and classes and makes it more structured and easy to manage

OOPS aims to manage dependencies by selectively inverting certain key dependencies in your architecture to prevent rigidity, fragility and non-reusability.

Class

• A class is a user defined blueprint from which objects are created
• Represents the set of properties and methods common to all objects

Object

• Basic unit of OOP that represents real-life entities.
• Instance of a class

4 Pillars of Java OOPS Concepts

1. Abstraction
2. Encapsulation
3. Inheritance
4. Polymorphism

1. Abstraction

• Only the essential details are displayed to the user
• Separates the What from the How
• Abstraction is achieved by Interfaces and Abstract classes

Example

Creating a service interface with it’s implemented class. Here, we make use of the interface and it’s method in the controller layer

This hides implementation details and allows us to change or swap out implementations.

2. Encapsulation

• Data hiding
• Binds together variables and methods in a single class
• The variables can only be manipulated by the class’s methods

Example

Getter and Setter methods

3. Inheritance

• Achieved by using extends keyword
• Supports reusability of code (DRY)

Note

The super() method is implicitly called at the initialization of a child class if the parent has a No Args constructor. If there is no No Args constructor, we need to explicitly call the super() method in the child class’s constructor. Failing to do so will cause compilation error.

4. Polymorphism (many forms)

• Ability to differentiate between entities with the same name efficiently

2 Types of polymorphism in Java -

1. Method overloading: Compile time polymorphism

• More than 1 method share the same name with different parameters (different signature) in a class.

2. Method overriding: Runtime polymorphism/ Dynamic binding

• Child class has the same method as the parent class, the implementation of the child class is used.
• Any subclass can be used wherever a parent class is expected

Example

DI a concrete class to an interface argument

Advantages

• Reusability
• Logical and layered structure
• Modular components

Disadvatages

• Can use more memory
• Can feel too heavy