Jtextfield somente numero (,)virgula

package caixa;

import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.text.*;

public class jTextOnlyNumber extends JFrame{

JTextField txtJT;

public jTextOnlyNumber(){
setTitle("TextField somente numeros");

Container contentPane = getContentPane();
contentPane.setLayout(null);
txtJT = new JTextField();
txtJT.setDocument(new NumberDocument());
txtJT.setBounds(16, 24, 185, 25);
contentPane.add(txtJT);
setSize(250, 100);
setVisible(true);
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});

}
public class NumberDocument extends PlainDocument{

public NumberDocument(){
super();

}
public void insertString(int offset, String str, AttributeSet attr) throws BadLocationException {
//permite apenas uma virgula
if(str.equals(",")){
if(txtJT.getText().indexOf(",")>-1)
return;
else
super.insertString(offset, str, attr);
}
if (str.codePointAt(0) < 48 || str.codePointAt(0) > 57)	return;
super.insertString(offset, str, attr);
}
}
public static void main(String args[]){
jTextOnlyNumber jt = new jTextOnlyNumber();
}
}

public class teste extends javax.swing.JFrame {

    /** Creates new form teste */
    public teste() {
        initComponents();
    }
 private void jSair2ActionPerformed(java.awt.event.ActionEvent evt) {
        
        this.dispose();
}

    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new teste().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify
    private javax.swing.JButton jSair2;
    private javax.swing.JTextField valor;
    // End of variables declaration

}