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JTextField Difficulty

Posted on 2001-08-07
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Last Modified: 2010-12-01
I need to do following things on a JTextField

1. Make sure only numbers are entered. Meaning that when a user presses a character on the keyboard nothing happens on the JTextField

2. Limit the entry to 4 digits.

3. Not allow -ve values

4. Once a valid value is entered, then on the enter key do something.

Please help me with this. Since I have tried all possible things in my capacity to figure out how to accomplish this.

Thanks In Advance

Bijoy
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Comment
Question by:bijoyn
  • 3
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6 Comments
 
LVL 15

Expert Comment

by:mohan_sekar
ID: 6360092
Hi,

        He is the code I am using to enter only numbers

 
    Put a filtering document in you JTextField is best.
  Here is the class that I use to filter out thing basis on the  
  mask string.
 
  In you application, You only need to do:
 
 
      JTextField jtf = new JTextField(();
      //
      // Only allow numeric 0,1,2,3,4,5,6,7,8,9 to be entered
      //
      jtf.setDocument(new MyTextFilter(MyTextFilter.NUMERIC));
 
  Let me know if you need further help.  Have fun!
 
//
// file MyTextFilter.java
//
import com.sun.java.swing.text.AttributeSet;
import com.sun.java.swing.text.BadLocationException;
import com.sun.java.swing.text.PlainDocument;
 
public class MyTextFilter
  extends PlainDocument
{
  public static final String LALPHA        =
"abcdefghijklmnopqrstuvwxyz";
  public static final String UALPHA        =
"ABCDEFGHIJKLMNOPQRSTUVWXYZ";
  public static final String ALPHA         = LALPHA + UALPHA;
  public static final String NUMERIC       = "0123456789";
  public static final String ALPHA_NUMERIC = ALPHA + NUMERIC;
  public MyTextFilter()
  {
    this(ALPHA_NUMERIC);
  }
  public MyTextFilter(String p_charset)
  {
    m_charset = p_charset;
  }
  public void insertString(int          p_offset,
                           String       p_str,
                           AttributeSet p_attr)
    throws BadLocationException
  {
    if (p_str == null)
      return;
 
    for (int i=0; i<p_str.length(); i++)
      if (m_charset.indexOf(p_str.valueOf(p_str.charAt(i))) == -1)
        return;
     
    super.insertString(p_offset, p_str, p_attr);
  }
 
  /**
   * the allow input character set
   */
  protected String m_charset = null;
}

:-)

bye

Mohan
0
 
LVL 15

Expert Comment

by:mohan_sekar
ID: 6360130
Hi again,


       Here is the code to limit the no. of characters.
---------------------------------

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

public class LimitedPlainDocument extends DFPlainDocument
{
        public LimitedPlainDocument (int maxLength)
        {
                this.maxLength = maxLength;
        }

        private int maxLength;
       
        public final int getMaxLength()
                {
                        return maxLength;
                }
       
        public final void setMaxLength (int maxLength)
                {
                        this.maxLength = maxLength;
                }
       
        public void insertString (int offs, String str, AttributeSet a)
throws
BadLocationException
        {
                if (str == null || getLength() + str.length() <= maxLength)
                            super.insertString (offs, str, a);
                else
                {
                        int remainder = maxLength - getLength();
                        if (remainder > 0)
                                super.insertString (offs, str.substring (0,
remainder), a);
                }
        }
}

call jTextField.setDocument(new LimitedPlainDocument(5));

and u won't be able to enter more than 5 chars even using Clipboard operations.

:-)

bye

Mohan
0
 
LVL 15

Accepted Solution

by:
mohan_sekar earned 300 total points
ID: 6360180
Hi again,

         Here is the code to filter -ive numbers

import java.awt.Toolkit;

import javax.swing.text.*;


/**
 * Document to only allow numbers.
 * <p>
 * @author Mike Foley
 **/
public class TextFilterDocument extends PlainDocument {

    /**
     * Valid number strings.
     **/
    public static final String NUMBERS = "0123456789";


    /**
     * TextFilterDocument, constructor
     **/
    public TextFilterDocument()
{
        super();
}


    /**
     * A String is being inserted into the Document.
     * Ensure that all characters are in NUMBERS.
     *
     * @param offset Where the new string goes.
     * @param string The String to be inserted after check.
     * @param attributeSet Attributes for the new string.
     **/
    public void insertString( int offset, String string,
                              AttributeSet attributeSet )
        throws BadLocationException {

        //
        // If nothing to insert, do nothing.
        //
        if( string == null )
            return;

        //
        // Ensure each character in the string is a number.
        //
        for( int i = 0; i < string.length(); i++ ) {
            if( NUMBERS.indexOf( string.valueOf(
                string.charAt(i) ) ) == -1 ) {
                   
                //
                // Not a number, don't insert the string.
                // Beep to let the user know something is wrong.
                //
                Toolkit.getDefaultToolkit().beep();
                return;
            }
        }

        //
        // Let our parent do the real work.
        //
        super.insertString( offset, string, attributeSet );

    }  // insertString

}  // TextFilterDocument

call the code using the following statement

JTextField integerTextField = new JTextField( new TextFilterDocument() );

I hope I have solved ur problems!!

;-)

bye

Mohan



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LVL 3

Expert Comment

by:rkenworthy
ID: 6360362
here's my simplified solution:

class DocumentListenerExample extends JPanel implements DocumentListener, KeyListener {

  JTextField Field = null;

  public class DocumentListenerExample() {
    Field = new JTextField();
    getContainer().add(Field);
    Field.getDocument().addDocuementListener(this);
    Field.addKeyListener(this);
  }

  public void changeUpdate(DocumentEvent evt) { }

  public void insertUpdate(DocumentEvent evt) {
    removeUpdate(evt);
  }

  public void removeUpdate(DocumentEvent evt) {
    String error = validate(Field.getText());
    if (error != null) {
      //System.out.println("Error: " + error);
      // show dialog or something...
    }
  }

  protected String validate(String text) {
    int num = -1;
    try {
      num = Integer.parseInt(text);
    }
    catch (NumberFormatException e) {
      return e.getText();
    }

    if (num < 0) return "Number cannot be negative.";

    return null;
  }

  public void keyPressed(KeyEvent e) {}
  public void keyReleased(KeyEvent e) {}

  public void keyTyped(KeyEvent e) {
    if ((int) e.getKeyChar() == KeyEvent.VK_ENTER) {
      //DO SOMETHING...
    }
  }

  public static final void main(String args[]) {
    JFrame f = new JFrame();
    f.getContainer().add(new DocumentListenerExample());
    f.pack();
    f.show()
  }
}


I didnt compile this program but should do the trick...

Hope it helps,
Rob
0
 

Author Comment

by:bijoyn
ID: 6360862
Hi Mohan & Rob

Thanks for the solutions. The difference between the two solutions are many. As I had specified. I wanted to restrict the user to input only 4 characters ( which Mohan gave me a solution ). The second was to input only numeric
values to the same textfield. this though Mohan has given me the solution. I am not sure how to combine the 1st and the second requirement together because u can setDocument to one class at a time. Also Mohan once u set the textfield to be numeric, u need not write the code for -ve numbers or do we ?.

Rob your solution allows me to enter non-numeric which is validated later. This is not what I wanted.

Mohan can u tell me how to combine the NUMERIC and the MAXLENGTH together in one Document class

Appreciate it.

Bijoy
0
 

Author Comment

by:bijoyn
ID: 6361059
Mohan,

I could combine the two functionalities within the same class and thanks a lot for your help.

Bijoy.
0

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