Re: Controlling content of text field

Hello,

I need to control content of text field in Swing.
I mean:
- user may enter only digits (0-9) and no other characters,
- there may by no more than 4 digits in text field,
- if value in text field is smaller than 50 or greater than 500,
    background of text field should become red -- if value
    it correct, background should be green.
All checkings should take place "on-line" (after each new
character(s) or after deleting of character(s)).

I created two working examples with use of a) JTextField
and b) JFormattedTextField.
I just wonder if there is some other (better) way to solve
my problem...?
Since I am new to Swing, I wish to learn correct methods
of solving basic problems. So, please tell me if my code is
good, and what are other possibilities. Thanks in advance!

Regards,
Robbo

------------------------
a)

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

public class Swing {
     public static void main(String[] args) {
         new Swing();
     }

     private static final int MIN = 50;
     private static final int MAX = 500;
     private static final int MAX_CHARS = 4;

     JTextField tf1 = null;

     public Swing() {
         JFrame f = new JFrame("Swing...");
         f.setSize(300, 120);
         Container c = f.getContentPane();
         c.setLayout(new FlowLayout());
         f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         tf1 = new JTextField(10);
         MyDocument md = new MyDocument();
         tf1.setDocument(md);
         md.addDocumentListener(new MyDocumentListener());
         c.add(tf1);
         f.setVisible(true);
     }

     class MyDocument extends PlainDocument {
         @Override
         public void insertString(int ofs, String str,
javax.swing.text.AttributeSet a)
                                             throws
javax.swing.text.BadLocationException {
             if (str == null)
                 return;

             char[] t = new char[str.length()];
             int l = 0;
             for (int i = 0; i< str.length(); i++) {
                 char c = str.charAt(i);
                 if (Character.isDigit(c))
                    t[l++] = c;
             }

             if ((str.length() != l) || (ofs>= MAX_CHARS)) {
                 Toolkit.getDefaultToolkit().beep();
                 l = 0;
             }

             super.insertString(ofs, new String(t, 0, l), a);
         }
     }

     class MyDocumentListener implements DocumentListener {
         public void changedUpdate(DocumentEvent e) { }

         public void insertUpdate(DocumentEvent e) {
             funct();
         }

         public void removeUpdate(DocumentEvent e) {
             funct();
         }

         private void funct() {
             int i = 0;
             try {
                 i = Integer.valueOf(tf1.getText());
             } catch (NumberFormatException e) {
                 tf1.setBackground(Color.red);
                 return;
             }

             if ((i< MIN) || (i> MAX)) {
                 tf1.setBackground(Color.red);
             } else
                 tf1.setBackground(Color.green);
         }
     }
}
------------------------
b)

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

public class Swing {
     public static void main(String[] args) {
         new Swing();
     }

     private static final int MIN = 50;
     private static final int MAX = 500;

     JFormattedTextField ftf1 = null;

     public Swing() {
         JFrame f = new JFrame("Swing...");
         f.setSize(250, 100);
         Container c = f.getContentPane();
         c.setLayout(new BorderLayout());
         f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         try {
             ftf1 = new JFormattedTextField(new MaskFormatter("####"));
         } catch (java.text.ParseException e) {
             System.exit(1);
         }

         ftf1.getDocument().addDocumentListener(new MyDocumentListener());
         c.add(ftf1);
         f.setVisible(true);
     }

     class MyDocumentListener implements DocumentListener {
         public void changedUpdate(DocumentEvent e) { }

         public void insertUpdate(DocumentEvent e) {
             funct();
         }

         public void removeUpdate(DocumentEvent e) {
             funct();
         }

         private void funct() {
             int i = 0;
             try {
                 i = Integer.valueOf(ftf1.getText().trim());
             } catch (NumberFormatException e) {
                 ftf1.setBackground(Color.red);
                 return;
             }

             if ((i< MIN) || (i> MAX)) {
                 ftf1.setBackground(Color.red);
             } else
                 ftf1.setBackground(Color.green);
         }
     }
}