使用命令模式设计一个图形绘制系统，该系统可以绘制矩形、椭圆、三角形等图形，恢复和撤销功能。绘制类图并编程实现。java实现

好的，下面是命令模式的类图：


在这个类图中，我们可以看到以下几个角色：

- `Command`: 命令接口，定义了执行和撤销命令的方法。
- `ConcreteCommand`: 具体命令类，实现了命令接口，包含了一个对于接收者的引用，用于执行具体的操作。
- `Receiver`: 接收者，真正执行命令的对象。
- `Invoker`: 调用者，用于调用命令并管理命令的历史记录。
- `Client`: 客户端，负责创建命令对象并将其传递给调用者。

下面是一份基于该类图的 Java 代码实现：

// Command.java
public interface Command {
    void execute();
    void undo();
}

// RectangleCommand.java
public class RectangleCommand implements Command {
    private Receiver receiver;
    private int x1, y1, x2, y2;

    public RectangleCommand(Receiver receiver, int x1, int y1, int x2, int y2) {
        this.receiver = receiver;
        this.x1 = x1;
        this.y1 = y1;
        this.x2 = x2;
        this.y2 = y2;
    }

    @Override
    public void execute() {
        receiver.drawRectangle(x1, y1, x2, y2);
    }

    @Override
    public void undo() {
        receiver.eraseRectangle(x1, y1, x2, y2);
    }
}

// EllipseCommand.java
public class EllipseCommand implements Command {
    private Receiver receiver;
    private int x1, y1, x2, y2;

    public EllipseCommand(Receiver receiver, int x1, int y1, int x2, int y2) {
        this.receiver = receiver;
        this.x1 = x1;
        this.y1 = y1;
        this.x2 = x2;
        this.y2 = y2;
    }

    @Override
    public void execute() {
        receiver.drawEllipse(x1, y1, x2, y2);
    }

    @Override
    public void undo() {
        receiver.eraseEllipse(x1, y1, x2, y2);
    }
}

// TriangleCommand.java
public class TriangleCommand implements Command {
    private Receiver receiver;
    private int x1, y1, x2, y2, x3, y3;

    public TriangleCommand(Receiver receiver, int x1, int y1, int x2, int y2, int x3, int y3) {
        this.receiver = receiver;
        this.x1 = x1;
        this.y1 = y1;
        this.x2 = x2;
        this.y2 = y2;
        this.x3 = x3;
        this.y3 = y3;
    }

    @Override
    public void execute() {
        receiver.drawTriangle(x1, y1, x2, y2, x3, y3);
    }

    @Override
    public void undo() {
        receiver.eraseTriangle(x1, y1, x2, y2, x3, y3);
    }
}

// Receiver.java
public class Receiver {
    public void drawRectangle(int x1, int y1, int x2, int y2) {
        // 绘制矩形
    }

    public void eraseRectangle(int x1, int y1, int x2, int y2) {
        // 擦除矩形
    }

    public void drawEllipse(int x1, int y1, int x2, int y2) {
        // 绘制椭圆
    }

    public void eraseEllipse(int x1, int y1, int x2, int y2) {
        // 擦除椭圆
    }

    public void drawTriangle(int x1, int y1, int x2, int y2, int x3, int y3) {
        // 绘制三角形
    }

    public void eraseTriangle(int x1, int y1, int x2, int y2, int x3, int y3) {
        // 擦除三角形
    }
}

// Invoker.java
import java.util.Stack;

public class Invoker {
    private Stack<Command> undoStack = new Stack<>();
    private Stack<Command> redoStack = new Stack<>();

    public void execute(Command command) {
        command.execute();
        undoStack.push(command);
        redoStack.clear();
    }

    public void undo() {
        if (!undoStack.isEmpty()) {
            Command command = undoStack.pop();
            command.undo();
            redoStack.push(command);
        }
    }

    public void redo() {
        if (!redoStack.isEmpty()) {
            Command command = redoStack.pop();
            command.execute();
            undoStack.push(command);
        }
    }
}

// Client.java
public class Client {
    public static void main(String[] args) {
        Receiver receiver = new Receiver();
        Invoker invoker = new Invoker();

        // 创建命令对象
        Command command1 = new RectangleCommand(receiver, 10, 10, 100, 100);
        Command command2 = new EllipseCommand(receiver, 20, 20, 200, 100);
        Command command3 = new TriangleCommand(receiver, 30, 30, 150, 150, 200, 50);

        // 执行命令
        invoker.execute(command1);
        invoker.execute(command2);
        invoker.execute(command3);

        // 撤销命令
        invoker.undo();
        invoker.undo();

        // 重做命令
        invoker.redo();
    }
}

在这份代码中，我们使用了 `Receiver` 来表示真正执行命令的对象，`Invoker` 用于调用命令并管理命令的历史记录，而 `Client` 则负责创建命令对象并将其传递给 `Invoker`。可以看到，每个具体命令类都包含了一个对于接收者的引用，这个引用在执行命令时被使用。同时，每个具体命令类也实现了 `undo()` 方法，用于撤销该命令所做的操作。