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备忘录模式在文本编辑器中的应用
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‎src/com/anxpp/designpattern/memento/textEditor/TextEditor.java‎

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package com.anxpp.designpattern.memento.textEditor;
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import java.util.LinkedList;
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//文本编辑器
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public class TextEditor {
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public static void main(String[] args) {
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//使用这个文本编辑器
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MyTextEditor editor = new MyTextEditor("这里是初始文本，可能为文件中读取的值。");
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System.out.println("开始修改文本：");
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editor.append("添加文字1");
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editor.delWords(); //删除最后一个
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// editor.delWords(2); //删除最后2个 这两个方法是没有问题的，这里避免控制台输出太多，取消这两次修改
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// editor.delWords(1,5); //删除前面5个
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System.out.println("开始恢复：");
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for(int i=0;i<10;i++) editor.recoverMemento();//恢复大于实际修改的次数不会出错，只会将文本设为o初始化状态
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System.out.println("开始重做：");
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for(int i=0;i<10;i++) editor.redo(); //重做大于实际恢复的次数不会出错，只会将文本设为最后状态
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System.out.println("再次恢复：");
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for(int i=0;i<10;i++) editor.recoverMemento();//恢复大于实际修改的次数不会出错，只会将文本设为o初始化状态
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System.out.println("再次重做：");
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for(int i=0;i<10;i++) editor.redo(); //重做大于实际恢复的次数不会出错，只会将文本设为最后状态
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System.out.println("再次恢复：");
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for(int i=0;i<10;i++) editor.recoverMemento();//恢复大于实际修改的次数不会出错，只会将文本设为o初始化状态
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editor.append("添加文字2");
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System.out.println("再次重做：");
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for(int i=0;i<10;i++) editor.redo(); //重做大于实际恢复的次数不会出错，只会将文本设为最后状态
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}
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}
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interface IMemento {}
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//发起人兼负责人
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class MyTextEditor {
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public StringBuffer text;
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private LinkedList<IMemento> mementos; //保存快照
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private LinkedList<IMemento> undos; //保存撤销的操作
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public MyTextEditor(){
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this("");
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}
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public MyTextEditor(String defaultStr){
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text = new StringBuffer(defaultStr);
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mementos = new LinkedList<IMemento>();
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undos = new LinkedList<IMemento>();
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print();
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}
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public void clearHistory(){
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mementos.clear();
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undos.clear();
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}
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public void append(String appendStr){
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if(appendStr==null||appendStr.length()==0) return;
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createMemento();
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text.append(appendStr);
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print();
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undos.clear();
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}
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//删除最后一个
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public void delWords(){
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delWords(1);
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}
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//删除最后n个
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public void delWords(int n){
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if(n<1||n>text.length()) return;
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delWords(text.length()-n+1,text.length());
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}
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//删除中间start到end的字符,第一个文字为第一个(而不是0)
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public void delWords(int start,int end){
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if(start<1 || end>text.length()+1) return;
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createMemento();
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text = text.delete(start-1, end);
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print();
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}
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public void reset(String text){
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this.text = new StringBuffer(text);
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}
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//新的快照
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public void createMemento(){
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mementos.push(new Memento(this));
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}
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//恢复状态
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public boolean recoverMemento(){
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Memento memento = (Memento) mementos.poll();
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if(memento==null) return false;
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undos.push(new Memento(this));
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reset(memento.state);
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print();
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return true;
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}
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//redo,redo的操作也可以恢复！
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public boolean redo(){
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Memento memento = (Memento) undos.poll();
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if(memento==null) return false;
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createMemento();
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reset(memento.state);
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print();
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return true;
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}
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//内部类实现备忘录
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private class Memento implements IMemento{
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private String state;
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private Memento(MyTextEditor editor){
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this.state = editor.text.toString();
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}
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}
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void print(){
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System.out.println("当前文本：" + text);
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}
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}

‎src/com/anxpp/designpattern/memento/textEditor/package-info.java‎

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/**
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* @author Administrator
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* 备忘录模式的应用
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*/
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package com.anxpp.designpattern.memento.textEditor;

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