title: Make calculator check data-type and output a message?
body: <p>i'm really new to Java and i'm trying to make a basic calculator, I've managed to get it to work and produce a double as i desired. My problem is that i want it to provide an error message if user inputs the wrong data type e.g. String</p>
  
  <pre><code>package com.company;
  
  import java.util.Scanner;
  
  public class Main {
  
  public static void main(String[] args) {
      double n1, n2;
      String n3;
      Scanner inp = new Scanner(System.in);
  
  
      System.out.print("Enter first value: ");
      String inp1 = inp.nextLine();
      n1 = Double.parseDouble(inp1);
  
  
      System.out.print("Enter Second Value: ");
      String inp2 = inp.nextLine();
      n2 = Double.parseDouble(inp2);
  
  
      System.out.print("Enter Operation: ");
      String inp3 = inp.nextLine();
  
      switch (inp3) {
  
          case "+":
              System.out.println("The result is: " + (n1 + n2));
              break;
          case "-":
              System.out.println("The result is: " + (n1 - n2));
              break;
          case "*":
              System.out.println("The result is: " + (n1 * n2));
              break;
          case "/":
              System.out.println("The result is: " + (n1/n2));
              break;
          default:
              System.out.println("Invalid Operation! \nPlease use '-,+,*,/' ");
  
      }
  
  }
  
  }
  </code></pre>
  
  <p>Here's my code at the moment, im open to any constructive criticism to improve my code. I can't seem to figure out a way to solve my problem!
  Thanks for any help :) </p>