How to make a menu re-appear in java

Question

import java.util.*;
public class LabTest1
{
public static void main(String[] args) 
    {
        Scanner console = new Scanner(System.in);
        double Choice1;
        double Choice2;
        int MenuChoice;
        System.out.print("Please enter the length: ");
        Choice1 = console.nextDouble();

        System.out.print("Please enter the width: ");
        Choice2 = console.nextDouble();

        System.out.println("=============================");
        System.out.println("|   MENU SELECTION          |");
        System.out.println("=============================");
        System.out.println("| Options:                  |");
        System.out.println("| 1. Calculate the area     |");
        System.out.println("| 2. Calculate the perimeter|");
        System.out.println("| 3. Exit                   |");
        System.out.println("=============================");
        MenuChoice = console.nextInt();
        System.out.print(" Select option: ");

    switch (MenuChoice)
    {
    case 1:
        System.out.println("Calculate the area selected");   
        System.out.println(Choice1 * Choice2);
        break;
    case 2:
      System.out.println(" Calculate the perimeter selected");  
      System.out.println(2*(Choice1 + Choice2));
      break;
    case 3:
        System.out.println("Exit selected");
        System.out.println(Choice1 + Choice2);
        break;

    default:
        System.out.println("Invalid selection");
        break; 
    }

    }
}

I need to make it so if the values are equal it should display a message saying that the values represent a square and allow the user to re-enter the values untill appropriate vlaues are entered ( yes i know a square is a rectangle)

Answer 1

Use the following pattern to ask for input, reject invalid input and loop:

boolean isValidInput = false;
[print prompt for input]
while (!isValidInput) {
   input = ...
   if (input is not valid) {
       print [invalid input, what is right form]
   } else {
       isValidInput = true;
   }
 }

By the way, you should use the minimum text possible. Print the request and what you are doing once, and the prompt for bad input each time they enter wrong information.