Only allowing numbers and a symbol (-) to be typed into a JTextField

Question

I\'m trying to create a math quiz and I only want the user to be able to enter numbers whether they\'re negative or positive. Is there any way to do so? I\'ve thought of u

Answer 1

Use DocumentFilter:

NumberOnlyFilter.java:

import javax.swing.*;
import javax.swing.text.*;
import java.util.regex.*;
public class NumberOnlyFilter extends DocumentFilter
{

    public void insertString(DocumentFilter.FilterBypass fb, int offset, String text, AttributeSet attr) throws BadLocationException
    {
        StringBuilder sb = new StringBuilder();
        sb.append(fb.getDocument().getText(0, fb.getDocument().getLength()));
        sb.insert(offset, text);
        if(!containsOnlyNumbers(sb.toString())) return;
        fb.insertString(offset, text, attr);
    }
    public void replace(DocumentFilter.FilterBypass fb, int offset, int length, String text, AttributeSet attr) throws BadLocationException
    {
        StringBuilder sb = new StringBuilder();
        sb.append(fb.getDocument().getText(0, fb.getDocument().getLength()));
        sb.replace(offset, offset + length, text);
        if(!containsOnlyNumbers(sb.toString())) return;
        fb.replace(offset, length, text, attr);
    }

    /**
     * This method checks if a String contains only numbers
     */
    public boolean containsOnlyNumbers(String text)
    {
        Pattern pattern = Pattern.compile("([+-]{0,1})?[\\d]*");
        Matcher matcher = pattern.matcher(text);
        boolean isMatch = matcher.matches();
        return isMatch;
    }

}

and then you can use it like:

((AbstractDocument)yourTxtField.getDocument()).setDocumentFilter(new NumberOnlyFilter());

Answer 2

You can use Integer.parseInt(String s, int radix), for decimal use 10 as a redix value.

Answer 3

Alternatively, consider Validating Input using an InputVerifier. A Formatted Text Field may also be suitable.