Creating a Text Area
The text area fires a document event whenever the text changes or some style on the text changes. 

  
 TextArea textArea = new JTextArea("Line1\nLine2");
 TextArea.getDocument().addDocumentListener(
   new MyDocumentListener());
     
 // The next two lines should be in one line.
 class MyDocumentListener implements 
   DocumentListener {
     public void insertUpdate(DocumentEvent evt) {
         // Some text was inserted.
     }
     public void removeUpdate(DocumentEvent evt) {
         // Some text was inserted.
     }
     public void changedUpdate(DocumentEvent evt) {
         // The style of some text was changed.
     }
 }