备忘录

public class Invoker {
	List<String> backupLib = new ArrayList<>(List.of(""));//新建空白文档
	private TextEditor receiver;
	int index = 0;
	
	public Invoker(TextEditor receiver) {
		this.receiver = receiver;
	}

	public Invoker invoke(Command c) {
		c.execute();
		if (!(c instanceof CopyCommand)) {//copy命令不备份数据
			if (index>0&&index < backupLib.size()-1) {//覆盖版本范围，从1到最新版本-1
				index++;
				backupLib.set(index, receiver.getState());
			} else {
				backupLib.add(receiver.getState());
				index++;
			}

		}
		
		return this;
	}

	public Invoker undo() {
		if (index > 0) {
			index--;
			restore(index);
		}
		return this;
	}

	public Invoker redo() {
		if (index < backupLib.size() - 1) {
			index++;
			restore(index);
		}
		return this;
	}

	public void restore(int index) {
		String restore = backupLib.get(index);
		receiver.setState(restore);
	}

}

//public class TextEditor下面添加



	//Memonto恢复备份

	public void setState(String state) {

		buffer.delete(0, buffer.length());//buffer清空方法，免创建对象

		buffer.append(state);

	}

//测试方法
public static void main(String[] args) {

		TextEditor editor = new TextEditor();

		Invoker inv=new Invoker(editor);

//		editor.add("Command pattern in text editor.\n");

		Command add=new AddCommand(editor, "Command pattern in text editor.\n");

		Command copy = new CopyCommand(editor);

//		copy.execute();

//		editor.add("----\n");

		Command add2=new AddCommand(editor, "----\n");

		Command paste = new PasteCommand(editor);

		inv.invoke(add);

		inv.invoke(copy);

		inv.invoke(add2);

		inv.invoke(paste);

		inv.undo();

		inv.invoke(add2);

		inv.undo();

		inv.redo();

//		inv.undo();

//		inv.invoke(add);

//		inv.undo();

//		inv.redo();

//		paste.execute();

		System.out.println(editor.getState());

	}