Author: Real Gagnon
Author's WebSite: http://tactika.com/realhome/realhome.html

The following class will help a JTextField to filter numeric or alphanumeric characters.

 import com.sun.java.swing.text.*;

 // or import javax.swing.text.*; if Java 2

  public class JTextFieldFilter extends PlainDocument {
    public static final String LOWERCASE  =
         "abcdefghijklmnopqrstuvwxyz";
    public static final String UPPERCASE  =
         "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    public static final String ALPHA   = 
         LOWERCASE + UPPERCASE;
    public static final String NUMERIC = 
         "0123456789";
    public static final String FLOAT = 
         NUMERIC + ".";
    public static final String ALPHA_NUMERIC = 
         ALPHA + NUMERIC;

    protected String acceptedChars = null;
    protected boolean negativeAccepted = false;
    
    public JTextFieldFilter() {
      this(ALPHA_NUMERIC);
      }
    public JTextFieldFilter(String acceptedchars) {
      acceptedChars = acceptedchars;
      }
   
    public void setNegativeAccepted(boolean negativeaccepted) {
      if (acceptedChars.equals(NUMERIC) ||
          acceptedChars.equals(FLOAT) ||
          acceptedChars.equals(ALPHA_NUMERIC)){
          negativeAccepted = negativeaccepted;
         acceptedChars += "-";
         }
       }

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

      if (acceptedChars.equals(UPPERCASE))
         str = str.toUpperCase();
      else if (acceptedChars.equals(LOWERCASE))
         str = str.toLowerCase();

      for (int i=0; i < str.length(); i++) {
        if (acceptedChars.indexOf(str.valueOf(str.charAt(i))) == -1)
          return;
        }

      if (acceptedChars.equals(FLOAT) || 
         (acceptedChars.equals(FLOAT + "-") && negativeAccepted)) {
         if (str.indexOf(".") != -1) {
            if (getText(0, getLength()).indexOf(".") != -1) {
               return;
               }
            }
         }

      if (negativeAccepted && str.indexOf("-") != -1) {
         if (str.indexOf("-") != 0 || offset != 0 ) {
            return;
            }
         }

      super.insertString(offset, str, attr);
    }
  }

Usage

  import java.awt.*; 
  import com.sun.java.swing.*;
  // or  import javax.swing.*;    if Java 2

   public class tswing extends JApplet{
     JTextField tf1,tf1b,tf1c,tf2,tf3;
     JLabel l1,l1b,l1c,l2,l3;

     public void init() {
       getContentPane().setLayout(new FlowLayout());
       //
       l1 = new JLabel("only numerics");
       tf1 = new JTextField(10);
       getContentPane().add(l1);
       getContentPane().add(tf1);
       tf1.setDocument
          (new JTextFieldFilter(JTextFieldFilter.NUMERIC));

       //
       l1b = new JLabel("only float");
       tf1b = new JTextField(10);
       getContentPane().add(l1b);
       getContentPane().add(tf1b);
       tf1b.setDocument
          (new JTextFieldFilter(JTextFieldFilter.FLOAT));

       //
       l1c = new JLabel("only float(can be negative)");
       tf1c = new JTextField(10);
       getContentPane().add(l1c);
       getContentPane().add(tf1c);
       JTextFieldFilter jtff = new JTextFieldFilter(JTextFieldFilter.FLOAT);
       jtff.setNegativeAccepted(true);
       tf1c.setDocument(jtff);

       //
       l2 = new JLabel("only uppercase");
       tf2 = new JTextField(10);
       getContentPane().add(l2);
       getContentPane().add(tf2);
       tf2.setDocument
          (new JTextFieldFilter(JTextFieldFilter.UPPERCASE));

       //
       l3 = new JLabel("only 'abc123%$'");
       tf3 = new JTextField(10);
       getContentPane().add(l3);
       getContentPane().add(tf3);
       tf3.setDocument
          (new JTextFieldFilter("abc123%$"));
       }
   }

Posted On: 5-Jul-1999

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