A Java Abstraction Example.

AbstractionExample.java

import java.util.Scanner;

public class AbstractionExample {

    public static void main(final String[] args) {
        Scanner scanner = new Scanner(System.in);
        Shape shape = null;
        System.out.println("AREA OF SHAPE");
        System.out.println("1. Rectange\n2. Square");
        System.out.print("Choice ? ");
        int choice = scanner.nextInt();        
        switch (choice) {
            case 1:
                shape = new Rectangle();
                System.out.print("Height Of Rectangle :: ");
                int height = scanner.nextInt();
                System.out.print("Width Of Rectangle :: ");
                int width = scanner.nextInt();
                shape.setHeight(height);
                shape.setWidth(width);
                System.out.print("Area Of Rectangle :: ");
                break;
            
            case 2:
                Square square = new Square();
                System.out.print("Side Of Square :: ");
                square.setSide(scanner.nextInt());
                shape = square;
                System.out.print("Area Of Square :: ");
                break;
        
            default:
                break;
        }
        System.out.println(shape.getArea());
        scanner.close();
    }

}

abstract class Shape {

    private int height = 0;
    private int width = 0;

    public int getHeight() {
        return height;
    }

    public void setHeight(final int height) {
        this.height = height;
    }

    public int getWidth() {
        return width;
    }

    public void setWidth(final int width) {
        this.width = width;
    }

    public abstract long getArea();
}

class Rectangle extends Shape{

    @Override
    public long getArea() {
        return getHeight()*getWidth();
    }

}

class Square extends Shape {

    private int side = 0;

    @Override
    public long getArea() {
        return getSide()*getSide();
    }

    public int getSide() {
        return side;
    }

    public void setSide(int side) {
        this.side = side;
    }
    
}