limiting user input for hexadecimal numbers

Question

Basically the User needs to input a Hexadecimal number which then converts it to decimal and binary numbers. I created two separate classes for the decimal and binary conversion and they work perfectly. What I wanted to do is to limit the input number making "90" the minimum input and "FF" the maximum one.

public static void main(String[] args) {
    ForwardorBack Binary = new ForwardorBack();
    Speed Decimal = new Speed();
    String Hexadecimal = "";
    Scanner input = new Scanner(System.in);
    System.out.println("Enter Hexadecimal Number");
    Hexadecimal = input.nextLine();
    while (Hexadecimal.length() > 2 || Hexadecimal.length() < 2) {
        System.out.println("Error Enter different number:");
        Hexadecimal = input.nextLine();
    }
    Decimal.wheels(Hexadecimal);
    Binary.move(Hexadecimal);
}

When posting on here, always use Java naming conventions. Variables are in camelCase; PascalCase is reserved for classes. — Boris the Spider
– Boris the Spider, Commented Mar 17, 2018 at 21:47
Use != 2 rather than both < 2 and > 2. Why not convert the input to an int to validate input and then easily compare if it is between 90 and 255 — Joakim Danielson
– Joakim Danielson, Commented Mar 17, 2018 at 22:27
there is no such thing, like number in decimal / hex / octal form. These are only formats on input/output, numeric sense is the same — Jacek Cz
– Jacek Cz, Commented Mar 17, 2018 at 22:48

Joakim Danielson · Accepted Answer · 2018-03-17 22:38:05Z

0

Here is a method to use in the head of the while loop

public static boolean validateInput(String input) {
  if  (input.length != 2) {
       return false;
  }

  //Replace with own conversion if needed
  try {
    int decimal = Integer.parseInt(hex, 16);
    if (decimal >= 90 && decimal <= 255) {
        return true;
    }
  } catch (NumberFormatException e) {
    return false;
  }
}

Then use it like so

while(!validateInput(hexadecimal)) {
  System.out.println("Error Enter different number:");
  hexadecimal = input.nextLine();
}

answered Mar 17, 2018 at 22:38

Joakim Danielson

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