Java tutorial
/* * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package javax.swing.undo; import java.io.Serializable; import javax.swing.UIManager; /** * An abstract implementation of <code>UndoableEdit</code>, * implementing simple responses to all boolean methods in * that interface. * * @author Ray Ryan */ @SuppressWarnings("serial") // Same-version serialization only public class AbstractUndoableEdit implements UndoableEdit, Serializable { /** * String returned by <code>getUndoPresentationName</code>; * as of Java 2 platform v1.3.1 this field is no longer used. This value * is now localized and comes from the defaults table with key * <code>AbstractUndoableEdit.undoText</code>. * * @see javax.swing.UIDefaults */ protected static final String UndoName = "Undo"; /** * String returned by <code>getRedoPresentationName</code>; * as of Java 2 platform v1.3.1 this field is no longer used. This value * is now localized and comes from the defaults table with key * <code>AbstractUndoableEdit.redoText</code>. * * @see javax.swing.UIDefaults */ protected static final String RedoName = "Redo"; /** * Defaults to true; becomes false if this edit is undone, true * again if it is redone. */ boolean hasBeenDone; /** * True if this edit has not received <code>die</code>; defaults * to <code>true</code>. */ boolean alive; /** * Creates an <code>AbstractUndoableEdit</code> which defaults * <code>hasBeenDone</code> and <code>alive</code> to <code>true</code>. */ public AbstractUndoableEdit() { super(); hasBeenDone = true; alive = true; } /** * Sets <code>alive</code> to false. Note that this * is a one way operation; dead edits cannot be resurrected. * Sending <code>undo</code> or <code>redo</code> to * a dead edit results in an exception being thrown. * * <p>Typically an edit is killed when it is consolidated by * another edit's <code>addEdit</code> or <code>replaceEdit</code> * method, or when it is dequeued from an <code>UndoManager</code>. */ public void die() { alive = false; } /** * Throws <code>CannotUndoException</code> if <code>canUndo</code> * returns <code>false</code>. Sets <code>hasBeenDone</code> * to <code>false</code>. Subclasses should override to undo the * operation represented by this edit. Override should begin with * a call to super. * * @exception CannotUndoException if <code>canUndo</code> * returns <code>false</code> * @see #canUndo */ public void undo() throws CannotUndoException { if (!canUndo()) { throw new CannotUndoException(); } hasBeenDone = false; } /** * Returns true if this edit is <code>alive</code> * and <code>hasBeenDone</code> is <code>true</code>. * * @return true if this edit is <code>alive</code> * and <code>hasBeenDone</code> is <code>true</code> * * @see #die * @see #undo * @see #redo */ public boolean canUndo() { return alive && hasBeenDone; } /** * Throws <code>CannotRedoException</code> if <code>canRedo</code> * returns false. Sets <code>hasBeenDone</code> to <code>true</code>. * Subclasses should override to redo the operation represented by * this edit. Override should begin with a call to super. * * @exception CannotRedoException if <code>canRedo</code> * returns <code>false</code> * @see #canRedo */ public void redo() throws CannotRedoException { if (!canRedo()) { throw new CannotRedoException(); } hasBeenDone = true; } /** * Returns <code>true</code> if this edit is <code>alive</code> * and <code>hasBeenDone</code> is <code>false</code>. * * @return <code>true</code> if this edit is <code>alive</code> * and <code>hasBeenDone</code> is <code>false</code> * @see #die * @see #undo * @see #redo */ public boolean canRedo() { return alive && !hasBeenDone; } /** * This default implementation returns false. * * @param anEdit the edit to be added * @return false * * @see UndoableEdit#addEdit */ public boolean addEdit(UndoableEdit anEdit) { return false; } /** * This default implementation returns false. * * @param anEdit the edit to replace * @return false * * @see UndoableEdit#replaceEdit */ public boolean replaceEdit(UndoableEdit anEdit) { return false; } /** * This default implementation returns true. * * @return true * @see UndoableEdit#isSignificant */ public boolean isSignificant() { return true; } /** * This default implementation returns "". Used by * <code>getUndoPresentationName</code> and * <code>getRedoPresentationName</code> to * construct the strings they return. Subclasses should override to * return an appropriate description of the operation this edit * represents. * * @return the empty string "" * * @see #getUndoPresentationName * @see #getRedoPresentationName */ public String getPresentationName() { return ""; } /** * Retreives the value from the defaults table with key * <code>AbstractUndoableEdit.undoText</code> and returns * that value followed by a space, followed by * <code>getPresentationName</code>. * If <code>getPresentationName</code> returns "", * then the defaults value is returned alone. * * @return the value from the defaults table with key * <code>AbstractUndoableEdit.undoText</code>, followed * by a space, followed by <code>getPresentationName</code> * unless <code>getPresentationName</code> is "" in which * case, the defaults value is returned alone. * @see #getPresentationName */ public String getUndoPresentationName() { String name = getPresentationName(); if (!"".equals(name)) { name = UIManager.getString("AbstractUndoableEdit.undoText") + " " + name; } else { name = UIManager.getString("AbstractUndoableEdit.undoText"); } return name; } /** * Retreives the value from the defaults table with key * <code>AbstractUndoableEdit.redoText</code> and returns * that value followed by a space, followed by * <code>getPresentationName</code>. * If <code>getPresentationName</code> returns "", * then the defaults value is returned alone. * * @return the value from the defaults table with key * <code>AbstractUndoableEdit.redoText</code>, followed * by a space, followed by <code>getPresentationName</code> * unless <code>getPresentationName</code> is "" in which * case, the defaults value is returned alone. * @see #getPresentationName */ public String getRedoPresentationName() { String name = getPresentationName(); if (!"".equals(name)) { name = UIManager.getString("AbstractUndoableEdit.redoText") + " " + name; } else { name = UIManager.getString("AbstractUndoableEdit.redoText"); } return name; } /** * Returns a string that displays and identifies this * object's properties. * * @return a String representation of this object */ public String toString() { return super.toString() + " hasBeenDone: " + hasBeenDone + " alive: " + alive; } }