Validate textbox in Graphical User Interface containing only numbers

Often it is necessary to validate the input data in the Graphical User Interface when received at the server side. According to the received parameters the server may be not called if the parameters are not in the desired format. This will lead to a saving in the used resources server side. This can be easily done by performing a basic validation on the properties of the object received. The validation proposed here below could be smaller by using regular expressions.
The programming code below just loop on a received string and determines if every character of the string is a digit isDigit(). The loop stops if a character is not a digit and returns false.




/**
*
* @author Jose Ferreiro
*/
public class Main {

/**
* This method checks if a String contains only numbers
*/
public boolean containsOnlyNumbers(String str) {

//It can't contain only numbers if it's null or empty...
if (str == null || str.length() == 0)
return false;

for (int i = 0; i < str.length(); i++) {

//If we find a non-digit character we return false.
if (!Character.isDigit(str.charAt(i)))
return false;
}

return true;
}


/**
* @param args the command line arguments
*/
public static void main(String[] args) {
Main main = new Main();
System.out.println(main.containsOnlyNumbers("123456"));
System.out.println(main.containsOnlyNumbers("123abc456"));
}
}


OUTPUT of the main method:
True
False

HAPPY CODING