Validate if input is not numeric (number)

Question

I am just a beginner. Am trying to validate if an input is numeric and not a string. I can't seem to get the correct result. It's always false.

import javax.swing.JOptionPane;

public class CheckDigit 
{
    public static void main(String[] args)
    {
        String containsOnlyNumbers;
        containsOnlyNumbers = JOptionPane.showInputDialog("Please enter some numbers: ");
        // System.out.println(containsOnlyNumbers("12345"));
        // System.out.println(containsOnlyNumbers("12abc345"));
        if (false)
        {
            JOptionPane.showMessageDialog(null, "False!");   
        }
        else
        {
            JOptionPane.showMessageDialog(null, "True!");  
        }  
    }

    public static boolean containsOnlyNumbers(String str)
    {
        for (int i = 0; i < str.length(); i++)
        {
            if (!Character.isDigit(str.charAt(i)))
                return false;
        }
        return true; 
    }
}

Please advise. TIA.

Do you need to do that yourself? If not try Apache Commons' `StringUtils` which has a method that does exactly what you want. — Thomas, Aug 11 '15 at 08:21
possible duplicate of [How to check if a String is a numeric type in Java](http://stackoverflow.com/questions/1102891/how-to-check-if-a-string-is-a-numeric-type-in-java) — , Aug 11 '15 at 08:21
What do you except to happen, if you use this statement `if (false)` — SomeJavaGuy, Aug 11 '15 at 08:23

score 1 · Accepted Answer · answered Aug 11 '15 at 08:24

1

If your want to use your solution you have to replace

if (false)

with

if (!containsOnlyNumbers(containsOnlyNumbers))

because you are not calling your method (same name for method and String).

answered Aug 11 '15 at 08:24

ageh

91
10

2

and also avoid using the same name for a variable and a method in the same scope – vefthym Aug 11 '15 at 08:27

score 0 · Answer 2 · answered Aug 11 '15 at 08:46

You can also try like this,

  public static boolean numericCheck(String str)
  {

  try{
          double d=Double.parseDouble(str);

      }catch(NumberFormatException e)
       {
          return false;
       }

   return true;

}

if method return true then input is a number, if return false input is not numeric

Validate if input is not numeric (number)

2 Answers2