This Java tip illustrates a method of matches bracket as user edits document. This tip extends parenthesis matcher tip and extends its functionality. The tip continuously colors as the user edits the document. This tip may also be termed as live parenthesis matcher.

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

public class LiveParenMatcher extends ParenMatcher implements DocumentListener {

  public LiveParenMatcher() {
    super();
    getDocument().addDocumentListener(this);
  }

  public void changedUpdate(DocumentEvent de) {
    // no insertion or deletion, so do nothing
  }

  public void insertUpdate(DocumentEvent de) {
    SwingUtilities.invokeLater(this); // will call run()
  }

  public void removeUpdate(DocumentEvent de) {
    SwingUtilities.invokeLater(this); // will call run()
  }

  public static void main(String[] args) {
    JFrame frame = new JFrame("LiveParenMatcher");
    frame.setContentPane(new JScrollPane(new LiveParenMatcher()));
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(300, 200);
    frame.setVisible(true);
  }

  // ---- finished from "The DocumentListener Interface" ----

  // ---- begin from "The DocumentEvent Interface" ----
  
  public void insertUpdate_2(DocumentEvent de) {
    Document doc = de.getDocument();
    int offset = de.getOffset();
    int length = de.getLength();
    String inserted = "";
    try {
      inserted = doc.getText(offset, length);
    } catch (BadLocationException ble) { }

    for (int j=0; j < inserted.length(); j+=1) {
      char ch = inserted.charAt(j);
      if (ch == '(' || ch == '[' || ch == '{' ||
          ch == ')' || ch == ']' || ch == '}'  ) {
        SwingUtilities.invokeLater(this); // will call run()
        return; // no need to check further
      }
    }
  }

  // ---- begin from "The Segment Class" ----

  public void insertUpdate_3(DocumentEvent de) {
    Document doc = de.getDocument();
    int offset = de.getOffset();
    int length = de.getLength();
    Segment seg = new Segment();
    try {
      doc.getText(offset, length, seg); // text placed in Segment
    } catch (BadLocationException ble) { }

    // iterate through the Segment
    for (char ch = seg.first(); ch != seg.DONE; ch = seg.next())
      if (ch == '(' || ch == '[' || ch == '{' ||
          ch == ')' || ch == ']' || ch == '}'  ) {
        SwingUtilities.invokeLater(this); // will call run()
        return; // no need to check further
      }
  }

  // ---- begin from "The ElementIterator Class" ----

  public void removeUpdate_2(DocumentEvent de) {
    // print some debugging information before matching the parens
    ElementIterator iter = new ElementIterator(de.getDocument());

    for (Element elem = iter.first(); elem != null; elem = iter.next()) {
      DocumentEvent.ElementChange change = de.getChange(elem);
      if (change != null) { // null means there was no change in elem
        System.out.println("Element "+elem.getName() + " (depth " +
            iter.depth()+") changed its children: " +
            change.getChildrenRemoved().length+" children removed, " +
            change.getChildrenAdded().length+" children added.\n");
      }
    }
    SwingUtilities.invokeLater(this); // will call run()
  }

}