Repeating Menu Example

import java.util.Scanner;

public class MathMenu {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        //Geometry geometry = new Geometry();

        int choice = 0;

        // Loops indefinitely until the user enters an int between 1 and 4 (inclusive).
        while(choice < 1 || choice > 4) {
            System.out.println("1. Calculate the Area of a Circle");
            System.out.println("2. Calculate the Area of a Rectangle");
            System.out.println("3. Calculate the Area of a Triangle");
            System.out.println("4. Quit");

            // This line will prevent instantaneous looping, aka the terrible Infinite Loop!
            choice = input.nextInt();
        }

        switch (choice)
        {
        case 1:
            System.out.println("Radius of circle");
            double r = input.nextDouble();
            //System.out.println("Area: " + geometry.areaOfCircle(r));
            break;
        case 2:
            double l, w;
            System.out.println("Length of rectangle");
            l = input.nextDouble();
            System.out.println("Width of rectangle");
            w = input.nextDouble();
            //System.out.println("Area: " + geometry.areaOfRectangle(l, w));
            break;
        case 3:
            double b, h;
            System.out.println("Base of triangle");
            b = input.nextDouble();
            System.out.println("Height of triangle");
            h = input.nextDouble();
            //System.out.println("Area: " + geometry.areaOfTriangle(b, h));
            break;
        case 4:
            System.out.println("Quitting");
            input.close();
            System.exit(0);
            break;
        default:
            System.out.println("This should be unreachable, if this prints... well oh dear!");
            input.close();
            System.exit(-1);
            break;
        }

        input.close();
    }
}