Java OOPS – Part 3 – Data abstraction with examples

Abstraction is method of hiding the implementation details and showing only the functionality, basicallyProvides guidelines to build a standard product.

Example –

You know how a car look like and how to drive, but you don’t know how to build a car.

For detailed explanation –

Types of abstraction –

Abstraction can be achieved by 2 types

• Abstract
• Interface

Abstract –

• Abstract class will have mix of implemented and un implemented methods
• Syntax – abstract class ClassName
• An abstract class may or may not contain abstract methods
• If at least one method is abstract, then the class should be declared as abstract
• Can not create an object of an Abstract class
• Child class that inherit abstract class with abstract methods, should implement all the abstract methods
• Abstract class can have constructors

Code implementation – 

Shape.java

—-Circle.java

—-Rectangle.java

package abstraction;

public abstract class Shape {	
	String Color;
	double Area;
	
	Shape(String Color){
		this.Color = Color;
		System.out.println("Color of shape - " + this.Color);
	}
	
	abstract double calcArea();
	
	void DispArea(double Area){
		this.Area = Area;
		System.out.println("Area - " + this.Area);
	}
}

package abstraction;

public class Circle extends Shape{

	double Area;
	double pi = 3.14;
	double radius;
	
	Circle(String Color) {
		super(Color);
	}

	@Override
	double calcArea() {
		Area = pi * radius * radius;
		return Area;
	}
	
	public static void main(String[] args) {
		Circle circle = new Circle("Green");
		circle.radius = 5;
		
		circle.DispArea(circle.calcArea());
	}
}

package abstraction;

public class Rectangle extends Shape{

	double Area;
	double length;
	double breath;
	
	Rectangle(String Color) {
		super(Color);
	}

	@Override
	double calcArea() {
		Area = length * breath;
		return Area;
	}
	
	public static void main(String[] args) {
		Rectangle rect = new Rectangle("Red");
		rect.length = 5;
		rect.breath = 10;
		
		rect.DispArea(rect.calcArea());
	}
}

Interface –

• Interface should have all unimplemented methods.
• Syntax – interface InterfaceName
• All the methods in interface are abstract
• Can not create an object of an interface
• All the fields of an interface must be declared as static final
• An interface is implemented by a class
• An interface is extended by multiple interface

Code implementation – 

package interfaceEx;

interface Shape {
	
	double calcArea();
	String GetColor();
	void DispColor();
	void DispArea();
}

package interfaceEx;

public class Circle implements Shape{
	double Area;
	double pi = 3.14;
	double radius;

	@Override
	public double calcArea() {
		Area = pi * radius * radius;
		return Area;
	}

	@Override
	public String GetColor() {
		return "Green";
	}

	@Override
	public void DispColor() {
		System.out.println(GetColor());		
	}

	@Override
	public void DispArea() {
		System.out.println(calcArea());
	}
	
	public static void main(String[] args) {
		Circle circle = new Circle();
		circle.radius = 4;
		circle.GetColor();
		circle.DispColor();
		circle.DispArea();
	}
}

package interfaceEx;

public class Rectangle implements Shape{

	double Area;
	double length;
	double breath;
	
	@Override
	public String GetColor() {
		return "Green";
	}

	@Override
	public double calcArea() {
		Area = length * breath;
		return Area;
	}
	
	@Override
	public void DispColor() {
		System.out.println(GetColor());
	}

	@Override
	public void DispArea() {
		System.out.println(calcArea());
	}

	public static void main(String[] args) {
		Rectangle rect = new Rectangle();
		rect.length = 5;
		rect.breath = 10;
		rect.DispArea();
		rect.DispColor();
	}
}