import java.util.Scanner;

public class CalculateAreaOfShapes{
    public static void main(String []args){
        int choice;
        Scanner scanner=new Scanner(System.in);
        System.out.println("1.For circle area.");
        System.out.println("2.For square area ");
        System.out.println("3.For Rectangle area");
        System.out.println("Input your choice : ");
        choice=scanner.nextInt();
        switch(choice){
        case 1: System.out.println("Input radius of circle : ");
                float radius=scanner.nextFloat();
                float pi=(float) 3.14;
                float area=pi*radius*radius;
                System.out.println("Area of circle = "+area);
                break;
        case 2:System.out.println("Input side of square : ");
                float length=scanner.nextFloat();
                area=length*length;
                System.out.println("Area of your square = "+area);
                break;
        case 3:System.out.println("Input length of rectangle : ");
               length =scanner.nextFloat();
               System.out.println("Input width of rectangle : ");
               float width=scanner.nextFloat();
               area=length*width;
               System.out.println("Area of rectangle = "+area);
               break;
        default: System.out.println("Your choice is not correct.");       
        }
    }
}

Description :Here we are calculating area of 3 shapes according to user choice. If user input 1 then we calculate circle area as Formula

area of circle=3.14*radius*radius

If User's choice is 2 then your program give you output of square area. Formula of square-

area of Square=length*width; where length and width are same

If choice is 3 then it will generate area of rectangle.Formula is -

Area of rectangle = length*width .