Maskformatter leaving empty space

Question

In my project, I have an age field, where I want to receive at most 3 number, so I did this :

mskIdade = new MaskFormatter("###");

so far so good, but every time I type a number with less than 3 characters, the mskIdade fills the remaining fields with empty spaces (" "). I’m pretty sure that’s because ### oblige the field to be left with three characters. As I can not force the field to be 3 characters long and accept it only numbers ?

Answer 1

You can use the Trim() in your String, to remove left and right empty spaces from the value:

String str = formattedTextField.getText().trim();

---

Another way, maybe it’s even better to give you more control than is typed, is by using the class Plaindocument. With it, you not only control the amount of characters you type, but you also want just numbers:

class JTextFieldLimit extends PlainDocument {

    private int limit;

    JTextFieldLimit(int limit) {
        super();
        this.limit = limit;
    }

    @Override
    public void insertString(int offset, String str, AttributeSet attr) throws BadLocationException {
        if (str == null) {
            return;
        }

        if ((getLength() + str.length()) <= limit) {

            super.insertString(offset, str.replaceAll("\\D++", ""), attr);
        }
    }
}

Then just apply to any JTextfield:

    JTextFieldLimit limitDocument = new JTextFieldLimit(3);
    seuTextField.setDocument(limitDocument);

The signature of the method insertString receives three parameters:

• int offset = indicates which index of the current string in the field, the new will be added;

• String str = is the new string that will be added (digits, in your case);

• AttributeSet attr = are attributes of the string(like font type, font size and style, etc...), in this case, it made no difference to us.

In the str.replaceAll("\\D++", ""), I’m passing a Regular Expression that will remove any characters passed in the string that are not digits.

Remembering that the class builder JTextFieldLimit receives the character limit your field may have, and this class can be used in any text field.

Obs.: With the class shown above, you don’t need to use or MaskFormatter and neither JTextFormatterField.

References:

Limit Jtextfield input to a Maximum length(java2s)

How to implement in Java ( Jtextfield class ) to allow entering only digits?

Limiting the number of characters in a Jtextfield

Answer 2

I’ve made two methods that can help you with this problem:

Check if there are only numbers in a String.

public static boolean apenasNumeros(String text){
    return text.matches("[0-9]+");
}

Return only the numbers of a String.

public static String tirarTudoExcetoDigitos( String text) {
       if (text == null || text.length() == 0) {
           return "";
       }
       return text.replaceAll("\\D+", "");
    }

Small example:

public static void main(String[] args) {
    String test1 = "12345";
    System.out.println("Teste 1:");
    System.out.println("Apenas Números? " + apenasNumeros(test1));
    System.out.println("Apenas Números!! " + tirarTudoExcetoDigitos(test1));
    String test2 = "123A5";
    System.out.println("Teste 2:");
    System.out.println("Apenas Números? " + apenasNumeros(test2));
    System.out.println("Apenas Números!! " + tirarTudoExcetoDigitos(test2));
}

Upshot:

Teste 1:
Apenas Números? true
Apenas Números!! 12345
Teste 2:
Apenas Números? false
Apenas Números!! 1235