JAVA 兑现Undo/Redo（撤销/恢复）二

JAVA 实现Undo/Redo（撤销/恢复）二
三， DrawLineCommand，实现一次Undo/Redo功能

一个继承了UndoableCommand提供具体的撤销/恢复功能的子类，就可以实现一次Undo/Redo。这里实现一个在容器上画直线的子类DrawLineCommand，带有擦除和重画直线的功能。

import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import java.util.Random;

public class DrawLineCommand extends UndoableCommand {

    private int x1, y1, x2, y2;
    private Container container;

    public DrawLineCommand(Container container) {
        this.container = container;
        x1 = new Random().nextInt(100) + 100;
        y1 = new Random().nextInt(100) + 100;
        x2 = new Random().nextInt(100) + 300;
        y2 = new Random().nextInt(100) + 250;
    }

    @Override
    public void command() {
        drawLine(Color.RED);
        System.out.print("Draw a ");
        System.out.println(toString());
    }

    @Override
    public void restore() {
        drawLine(container.getBackground());
        System.out.print("Erase the ");
        System.out.println(toString());
    }

    private void drawLine(Color c) {
        Graphics g = container.getGraphics();
        g.setColor(c);
        g.drawLine(x1, y1, x2, y2);
        g.dispose();
    }

    @Override
    public String toString() {
        StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append("line between point(");
        stringBuilder.append(x1).append(",").append(y1).append(") and point(");
        stringBuilder.append(x2).append(",").append(y2).append(")");
        return stringBuilder.toString();
    }
}


下面给出一个UndoTest类来测试DrawLineCommand

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import javax.swing.*;

public class UndoTest extends JFrame {

    UndoableCommand command;
    Action drawLineAction, undoAction, redoAction;

    public UndoTest() {
        undoAction = new AbstractAction("Undo") {

            @Override
            public void actionPerformed(ActionEvent e) {
                command.undo();
                setEnabled(false);
                redoAction.setEnabled(true);
            }
        };
        undoAction.setEnabled(false);

        redoAction = new AbstractAction("Redo") {

            @Override
            public void actionPerformed(ActionEvent e) {
                command.redo();
                setEnabled(false);
                undoAction.setEnabled(true);
            }
        };
        redoAction.setEnabled(false);

        drawLineAction = new AbstractAction("Draw Line") {

            @Override
            public void actionPerformed(ActionEvent e) {
                command = new DrawLineCommand(getContentPane());
                command.execute();
                undoAction.setEnabled(true);
            }
        };
    }

    public void createAndShowGUI() {
        JToolBar toolBar = new JToolBar();
        toolBar.add(drawLineAction);
        toolBar.add(undoAction);
        toolBar.add(redoAction);
        add(toolBar, BorderLayout.NORTH);
        setSize(600, 400);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new UndoTest().createAndShowGUI();
            }
        });
    }
}

结果：DrawLineCommand能完美完成最近一次的Undo/Redo

可见，用UndoableCommand来实现一次Undo/Redo功能是可行的，那么如何实现多次或者无限制的Undo/Redo呢？