title: Java User input Validation
body: <p>I am trying to figure out how to validate the input of a user. I want the user to enter a double but if the user enters a string I want the question repeated until a double is entered. Iv'e searched but I couldn't find anything. Below is my code so far any help is appreciated. I have to use a do while loop I am stuck on what to put in the while loop to make sure the input is a double and not a string. </p>
  
  <pre><code>public class FarenheitToCelsius {
  
  /**
   * @param args the command line arguments
   */
  public static void main(String[] args) {
  
    double fahrenheit, celsius; 
    Scanner in = new Scanner(System.in);
    do{
      System.out.printf("Enter a fahrenheit degree: ");
      fahrenheit = in.nextDouble();
    }
    while();
  
    celsius = ((fahrenheit - 32)*5)/9;
  
    System.out.println("Celsius value of Fahrenheit value " + fahrenheit + " is " + celsius);
  </code></pre>