Allows you to enter only numbers and the symbol (-) in JTextField

Question

I am trying to create a math quiz and I want the user to be able to enter numbers regardless of whether they are negative or positive. Is there any way to do this? I thought about using regular expressions, but I heard that they are bad to use. I tried using keylistener, but then what if the user inserts? I tried to parse a string to get an integer, but then a negative character would not work.

Any ideas?

package com.quiz.ui; import java.awt.BorderLayout; import java.awt.event.KeyEvent; import java.awt.event.KeyListener; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.JTextField; public class SSCCE { private JFrame frame; private JPanel contentPane; private JTextField usernameField; public static void main(String[] arguments) { new SSCCE().construct(); } public void construct() { frame = new JFrame("Login"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.add(getContentPane()); frame.pack(); frame.setVisible(true); } public JPanel getContentPane() { usernameField = new JTextField(5); usernameField.addKeyListener(new KeyListener() { @Override public void keyPressed(KeyEvent arg0) { int keyCode = arg0.getKeyCode(); if ((keyCode > 47 && keyCode < 58) || keyCode == 45) { arg0.consume(); } System.out.println(arg0.getKeyCode()); } @Override public void keyReleased(KeyEvent arg0) { // TODO Auto-generated method stub } @Override public void keyTyped(KeyEvent arg0) { // TODO Auto-generated method stub } }); contentPane = new JPanel(new BorderLayout()); contentPane.add(usernameField); return contentPane; } } 

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

Alternatively, consider Validating Input with an InputVerifier . A A formatted text box may also be suitable.

Answer 3

You can use Integer.parseInt (String s, int radix), to decimal use 10 as the value of redix.