#眉標=Java
#副標=使用Java Swing輕鬆寫個Undoable程式(3)
＃大標＝javax.swing.text對Undoable的支援
＃作者＝文／侯捷


========<程式1>===============================
//in JTextArea
public JTextArea(Document doc, String text, int rows, int cols) {
    super();
    this.rows = rows;
    this.columns = cols;
    if (doc == null) {
        doc = createDefaultModel();
    }
    setDocument(doc);
    ...  
}
protected Document createDefaultModel() {
    return new PlainDocument();
}

//in JTextComponent 
public void setDocument(Document doc) {
    Document old = model;  
    ...	            
    model = doc;
}

public PlainDocument() {
    this(new GapContent());
}
=============<程式1 end>===========================

=======<程式2>==================================
public abstract class AbstractDocument 
                          implements Document, Serializable {
    ...
    private Content data;
    public interface Content { ... }
}
==========<程式2 end >==================================

=====================<程式3>=============
public class MyClass extends JFrame {
  protected JTextArea textArea = new JTextArea();
  protected UndoManager manager = new UndoManager();
  ...
  public MyClass() {  //ctor
    ...
    textArea.getDocument().addUndoableEditListener(
        new UndoableEditListener() {
          public void undoableEditHappened(UndoableEditEvent e) {
            manager.addEdit(e.getEdit());
            updateButtons();  //這是自定的method，用來更新按鈕狀態
          }
        });
    ...
  }
  public static void main(String argv[]) {
    new MyClass();
  }
}
======<程式３end>==============

========<程式4>=========================
PlainDocument.insertString()
  AbstractDocument.insertString()
      AbstractDocument.handleInsertString()
          GapContent.insertString()  
              new InsertUndo（產生一個UndoableEdit物件）
          PlainDocument.insertUpdate()
              AbstractDocument.insertUpdate()
          AbstractDocument.fireInsertUpdate()
          AbstractDocument.fireUndoableEditUpdate() //發送
              UndoableEditListener.undoableEditHappened()  //接收
=============<程式4 end>=========================

＝＝＝＝＝＝＝＝＝<程式5  GapContent.InsertUndo的詳細定義>==========
class InsertUndo extends AbstractUndoableEdit {
	protected InsertUndo(int offset, int length) {
	    super();
	    this.offset = offset;
	    this.length = length;
	}
	public void undo() throws CannotUndoException {
	    super.undo();
	    // Get the Positions in the range being removed.
	    posRefs = getPositionsInRange(null, offset, length);
	    string = getString(offset, length);
	    remove(offset, length);
	}
	public void redo() throws CannotRedoException {
	    super.redo();
	    insertString(offset, string);
	    string = null;
	    // Update the Positions that were in the range removed.
	    if(posRefs != null) {
		  updateUndoPositions(posRefs, offset, length);
		  posRefs = null;
	    }
	}
	/** Where string was inserted. */
	protected int offset;
	/** Length of string inserted. */
	protected int length;
	/** The string that was inserted. only be valid after undo. */
	protected String string;
	/** An array of instances of UndoPosRef for the Positions in the
	 * range that was removed, valid after undo. */
	protected Vector posRefs;
} 
================<程式5 end>===========================
========<程式6	GapContent.RemoveUndo的詳細定義。>========

class RemoveUndo extends AbstractUndoableEdit {
	protected RemoveUndo(int offset, String string) {
	    super();
	    this.offset = offset;
	    this.string = string;
	    this.length = string.length();
	    posRefs = getPositionsInRange(null, offset, length);
	}
	public void undo() throws CannotUndoException {
	    super.undo();
	    insertString(offset, string);
	    // Update the Positions that were in the range removed.
	    if(posRefs != null) {
		  updateUndoPositions(posRefs, offset, length);
	        posRefs = null;
	    }
	    string = null;
	}
	public void redo() throws CannotRedoException {
	    super.redo();
	    string = getString(offset, length);
	    // Get the Positions in the range being removed.
	    posRefs = getPositionsInRange(null, offset, length);
	    remove(offset, length);
	}
	/** Where the string was removed from. */
	protected int offset;
	/** Length of string removed. */
	protected int length;
	/** The string that was removed. valid when redo is valid. */
	protected String string;
	/** An array of instances of UndoPosRef for the Positions in the
	 * range that was removed, valid before undo. */
	protected Vector posRefs;
} 
======<程式6 end>===========
#中標=運行分析