How to get type of JTextfield from DocumentFilter

Question

Problem: I want to know whether can we get the JTextfield type from the DocumentFilter??
I have read java docs and searched a lot but did not find any information.

Need: I set same DocumentFilter on 2 JTextfields. When the event occur, in the "replace" method of DocumentFilter, I want to know action on which textfield resulted in the event.

Use Case: I have near about 15 texfields(may increase in future) and I want separate checks on all which are:
- maximum text length for input
- only certain characters must be entered(this will be same for all textfields)
For e.g: textfield1 can take maximum 10 chars but textfield2 can take maximum 5 chars.

What I have done so far:
I have created separate filters for every textfield which results in lots of redundant code and increases complexity to handle, for future use.

Looking forward for any help. :-)

Answer 1

Ok, now your need is more clear but, once again, you can't (and you should not) check which textfield are you typing in from inside the DocumentFilter to decide what to do in your replace () method.

Possible solution: create your own DocumentFilter class, passing all the parameters you need (maximum text length, and maybe an array of forbidden characters, or whatever else). All your textfields will have a distinct DocumentFilter instance, with the parameters set in order to suit your needs. This way you will have a clean solution without reduntant code.

For example:

import java.awt.GridLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.border.EmptyBorder;
import javax.swing.text.AbstractDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.DocumentFilter;
public class FilterTextField
{
    public static void main (String [] a) {
        SwingUtilities.invokeLater (new Runnable () {
            @Override public void run () {
                createAndShowGUI ();
            }
        });
    }
    private static void createAndShowGUI () {
        JFrame frame = new JFrame ("Test");
        frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
        frame.setContentPane (new MainPanel ());
        frame.pack ();
        frame.setLocationRelativeTo (null);
        frame.setVisible (true);
    }
}
class MainPanel extends JPanel
{
    public MainPanel () {
        super (new GridLayout (3, 1, 0, 20));

        JTextField t1 = new JTextField (20);
        JTextField t2 = new JTextField (20);
        JTextField t3 = new JTextField (20);

        ((AbstractDocument) t1.getDocument ()).setDocumentFilter (new MyDocumentFilter (5));
        ((AbstractDocument) t2.getDocument ()).setDocumentFilter (new MyDocumentFilter (10, '!', '?'));
        ((AbstractDocument) t3.getDocument ()).setDocumentFilter (new MyDocumentFilter (15, new char [] {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'}));

        add (t1);
        add (t2);
        add (t3);

        setBorder (new EmptyBorder (20, 20, 20, 20));
    }


}
class MyDocumentFilter extends DocumentFilter
{
    private char [] forbiddenCharacters;
    private int maximumLength;

    public MyDocumentFilter (int maximumLength, char ... forbiddenCharacters) {
        this.maximumLength = maximumLength;
        this.forbiddenCharacters = forbiddenCharacters;
    }
    @Override public void replace (FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
        // Get the full text you would have after replacement
        Document document = fb.getDocument ();
        String fullText = new StringBuilder (document.getText (0, document.getLength ())).replace (offset, offset + length, text).toString ();
        // Check your requirements ...
        if (fullText.length () <= maximumLength) {
            if (forbiddenCharacters != null) {
                for (char c : forbiddenCharacters) if (fullText.indexOf (c) > -1) return;
            }
            // Replace method is called only if your requirements are met.
            super.replace (fb, offset, length, text, attrs);
        }
    }
}