Java Tutorial/Swing Event/DocumentListener

DocumentListener and DocumentEvent

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/*
 * DocumentEventDemo.java requires no other files.
 */
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.Document;
public class DocumentEventDemo extends JPanel implements ActionListener {
  JTextField textField;
  JTextArea textArea;
  JTextArea displayArea;
  public DocumentEventDemo() {
    super(new GridBagLayout());
    GridBagLayout gridbag = (GridBagLayout) getLayout();
    GridBagConstraints c = new GridBagConstraints();
    JButton button = new JButton("Clear");
    button.addActionListener(this);
    textField = new JTextField(20);
    textField.addActionListener(new MyTextActionListener());
    textField.getDocument().addDocumentListener(new MyDocumentListener());
    textField.getDocument().putProperty("name", "Text Field");
    textArea = new JTextArea();
    textArea.getDocument().addDocumentListener(new MyDocumentListener());
    textArea.getDocument().putProperty("name", "Text Area");
    JScrollPane scrollPane = new JScrollPane(textArea);
    scrollPane.setPreferredSize(new Dimension(200, 75));
    displayArea = new JTextArea();
    displayArea.setEditable(false);
    JScrollPane displayScrollPane = new JScrollPane(displayArea);
    displayScrollPane.setPreferredSize(new Dimension(200, 75));
    c.gridx = 0;
    c.gridy = 0;
    c.weightx = 1.0;
    c.fill = GridBagConstraints.HORIZONTAL;
    gridbag.setConstraints(textField, c);
    add(textField);
    c.gridx = 0;
    c.gridy = 1;
    c.weightx = 0.0;
    c.gridheight = 2;
    c.fill = GridBagConstraints.BOTH;
    gridbag.setConstraints(scrollPane, c);
    add(scrollPane);
    c.gridx = 1;
    c.gridy = 0;
    c.weightx = 1.0;
    c.weighty = 1.0;
    gridbag.setConstraints(displayScrollPane, c);
    add(displayScrollPane);
    c.gridx = 1;
    c.gridy = 2;
    c.weightx = 0.0;
    c.gridheight = 1;
    c.weighty = 0.0;
    c.fill = GridBagConstraints.HORIZONTAL;
    gridbag.setConstraints(button, c);
    add(button);
    setPreferredSize(new Dimension(450, 250));
    setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
  }
  class MyDocumentListener implements DocumentListener {
    final String newline = "\n";
    public void insertUpdate(DocumentEvent e) {
      updateLog(e, "inserted into");
    }
    public void removeUpdate(DocumentEvent e) {
      updateLog(e, "removed from");
    }
    public void changedUpdate(DocumentEvent e) {
      // Plain text components don"t fire these events.
    }
    public void updateLog(DocumentEvent e, String action) {
      Document doc = (Document) e.getDocument();
      int changeLength = e.getLength();
      displayArea.append(changeLength + " character"
          + ((changeLength == 1) ? " " : "s ") + action + " "
          + doc.getProperty("name") + "." + newline + "  Text length = "
          + doc.getLength() + newline);
      displayArea.setCaretPosition(displayArea.getDocument().getLength());
    }
  }
  class MyTextActionListener implements ActionListener {
    /** Handle the text field Return. */
    public void actionPerformed(ActionEvent e) {
      int selStart = textArea.getSelectionStart();
      int selEnd = textArea.getSelectionEnd();
      textArea.replaceRange(textField.getText(), selStart, selEnd);
      textField.selectAll();
    }
  }
  /** Handle button click. */
  public void actionPerformed(ActionEvent e) {
    displayArea.setText("");
    textField.requestFocus();
  }
  /**
   * Create the GUI and show it. For thread safety, this method should be
   * invoked from the event-dispatching thread.
   */
  private static void createAndShowGUI() {
    // Create and set up the window.
    JFrame frame = new JFrame("DocumentEventDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    // Create and set up the content pane.
    JComponent newContentPane = new DocumentEventDemo();
    newContentPane.setOpaque(true); // content panes must be opaque
    frame.setContentPane(newContentPane);
    // Display the window.
    frame.pack();
    frame.setVisible(true);
  }
  public static void main(String[] args) {
    // Schedule a job for the event-dispatching thread:
    // creating and showing this application"s GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        createAndShowGUI();
      }
    });
  }
}

Get document from DocumentListener

import java.awt.BorderLayout;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
public class Test extends JFrame {
  JTextArea text = new JTextArea(10, 40);
  public Test() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    text.setLineWrap(true);
    text.getDocument().addDocumentListener(new DocumentListener() {
      public void showSize(DocumentEvent e) {
        System.out.println("Doc size: " + e.getDocument().getLength());
      }
      public void insertUpdate(DocumentEvent e) {
        showSize(e);
      }
      public void removeUpdate(DocumentEvent e) {
        showSize(e);
      }
      public void changedUpdate(DocumentEvent e) {
        showSize(e);
      }
    });
    getContentPane().add(
        new JScrollPane(text, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
            JScrollPane.HORIZONTAL_SCROLLBAR_NEVER), BorderLayout.CENTER);
    pack();
    setSize(200, 200);
  }
  public static void main(String[] args) {
    new Test().setVisible(true);
  }
}

How to Write a Document Listener

import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.Document;

class MyDocumentListener implements DocumentListener {
  final String newline = "\n";
  public void insertUpdate(DocumentEvent e) {
      updateLog(e, "inserted into");
  }
  public void removeUpdate(DocumentEvent e) {
      updateLog(e, "removed from");
  }
  public void changedUpdate(DocumentEvent e) {
      //Plain text components don"t fire these events.
  }
  public void updateLog(DocumentEvent e, String action) {
      Document doc = (Document)e.getDocument();
      int changeLength = e.getLength();
      System.out.println(
          changeLength + " character"
        + ((changeLength == 1) ? " " : "s ")
        + action + " " + doc.getProperty("name") + "."
        + newline
        + "  Text length = " + doc.getLength() + newline);
  }
}

public class UsingDocumentListener {
  public static void main(String[] a){
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JTextField textField = new JTextField();
    
    textField.getDocument().addDocumentListener(new MyDocumentListener());
    textField.getDocument().putProperty("name", "Text Field");
    frame.add(textField);
    frame.setSize(300, 200);
    frame.setVisible(true);
  }

}

Listening to JTextField Events with a DocumentListener

import java.awt.BorderLayout;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.Document;
public class AddingDocumentListenerJTextFieldSample {
  public static void main(String args[]) {
    final JFrame frame = new JFrame("Default Example");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JTextField textField = new JTextField();
    frame.add(textField, BorderLayout.NORTH);
    DocumentListener documentListener = new DocumentListener() {
      public void changedUpdate(DocumentEvent documentEvent) {
        printIt(documentEvent);
      }
      public void insertUpdate(DocumentEvent documentEvent) {
        printIt(documentEvent);
      }
      public void removeUpdate(DocumentEvent documentEvent) {
        printIt(documentEvent);
      }
      private void printIt(DocumentEvent documentEvent) {
        DocumentEvent.EventType type = documentEvent.getType();
        String typeString = null;
        if (type.equals(DocumentEvent.EventType.CHANGE)) {
          typeString = "Change";
        }  else if (type.equals(DocumentEvent.EventType.INSERT)) {
          typeString = "Insert";
        }  else if (type.equals(DocumentEvent.EventType.REMOVE)) {
          typeString = "Remove";
        }
        System.out.print("Type : " + typeString);
        Document source = documentEvent.getDocument();
        int length = source.getLength();
        System.out.println("Length: " + length);
      }
    };
    textField.getDocument().addDocumentListener(documentListener);
    
    frame.setSize(250, 150);
    frame.setVisible(true);
  }
}