Prompt user for console input and validate their response

Java 6.12.2015 No Comments

We often get students struggling to read and validate console input from the user. The following example gives a simple example of an approach that can be used.

It reads the input from the user and checks if it is a valid double. If its not it prompts the user again. Could easily be modified for different validation that you may require.

  Scanner input = new Scanner( );
  Double value = null;
  while (value==null) {
	  System.out.print("Please enter number: ");
	  String s = input.nextLine();
	  if (s.length()==0) {
		  System.out.println("You did not enter a value; Try again");
	  } else {
		  try {
			  value = new Double(s);
		  } catch (Exception ex) {
			  System.out.println("You did not enter a valid value; Try again");
  double d = value.doubleValue();

Leave a Reply