怎样判断文本区域中的内容是否更改

[blueball]

做一个文本编辑器，请问怎样判断文本区域中的内容是否更改（从而可以要求用户对其保存）？

[sunni]

点火！

[mymoto]

/**
* textÎĵµ¼àÌý
*/
class MyDocumentListener implements DocumentListener{
public void changedUpdate(DocumentEvent e){
}

public void insertUpdate(DocumentEvent e){
}
public void removeUpdate(DocumentEvent e){
}
}

[F1in2003]

public interface DocumentListener extends EventListener {

/**
* Gives notification that there was an insert into the document. The
* range given by the DocumentEvent bounds the freshly inserted region.
*
* @param e the document event
*/
public void insertUpdate(DocumentEvent e);

/**
* Gives notification that a portion of the document has been
* removed. The range is given in terms of what the view last
* saw (that is, before updating sticky positions).
*
* @param e the document event
*/
public void removeUpdate(DocumentEvent e);

/**
* Gives notification that an attribute or set of attributes changed.
*
* @param e the document event
*/
public void changedUpdate(DocumentEvent e);
}