java - JTextField in which the predefined text in not editable but other text can be appended to it?

Question

While going through Java swing I faced this problem. I have a JTextField which has predefined and not editable text. the user should be able to append other text to it but without editing the predefined text. Is there any method to obtain this solution or any other?

Answer 1

You can simply use a DocumentFilter:

import java.awt.FlowLayout;

import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.text.AbstractDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;

public class TestDocumentFilter {

    private static final String TEXT_NOT_TO_TOUCH = "You can't touch this!";

    private void initUI() {
        JFrame frame = new JFrame(TestDocumentFilter.class.getSimpleName());
        frame.setLayout(new FlowLayout());
        final JTextField textfield = new JTextField(50);
        textfield.setText(TEXT_NOT_TO_TOUCH);
        ((AbstractDocument) textfield.getDocument()).setDocumentFilter(new DocumentFilter() {
            @Override
            public void insertString(FilterBypass fb, int offset, String string, AttributeSet attr) throws BadLocationException {
                if (offset < TEXT_NOT_TO_TOUCH.length()) {
                    return;
                }
                super.insertString(fb, offset, string, attr);
            }

            @Override
            public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
                if (offset < TEXT_NOT_TO_TOUCH.length()) {
                    length = Math.max(0, length - TEXT_NOT_TO_TOUCH.length());
                    offset = TEXT_NOT_TO_TOUCH.length();
                }
                super.replace(fb, offset, length, text, attrs);
            }

            @Override
            public void remove(FilterBypass fb, int offset, int length) throws BadLocationException {
                if (offset < TEXT_NOT_TO_TOUCH.length()) {
                    length = Math.max(0, length + offset - TEXT_NOT_TO_TOUCH.length());
                    offset = TEXT_NOT_TO_TOUCH.length();
                }
                if (length > 0) {
                    super.remove(fb, offset, length);
                }
            }
        });
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(textfield);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new TestDocumentFilter().initUI();
            }
        });
    }

}