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上海企业名录地址电话,青岛招聘seo,镇江市住房和城乡建设局网站,南京搭建公司命令模式详解一、命令模式概述命令模式(Command Pattern)是一种行为型设计模式，它将请求封装为对象，从而允许使用不同的请求参数化其他对象，并支持请求的排队、记录、撤销等操作。核心特点解耦调用者与执行者：调用者无需知…

命令模式详解

一、命令模式概述

命令模式(Command Pattern)是一种行为型设计模式，它将请求封装为对象，从而允许使用不同的请求参数化其他对象，并支持请求的排队、记录、撤销等操作。

核心特点

解耦调用者与执行者：调用者无需知道具体执行细节
参数化请求：可将命令对象作为参数传递
支持撤销/重做：记录命令历史实现操作回滚
支持事务：实现命令的原子执行

二、命令模式的结构

主要角色

Command：抽象命令接口
ConcreteCommand：具体命令实现
Invoker：调用者/请求者
Receiver：命令接收者/执行者
Client：创建具体命令并设置接收者

三、命令模式的实现

1. 基本实现

// 命令接口
public interface Command {void execute();void undo();
}// 接收者 - 知道如何执行操作
public class Light {public void on() {System.out.println("开灯");}public void off() {System.out.println("关灯");}
}// 具体命令 - 开灯命令
public class LightOnCommand implements Command {private Light light;public LightOnCommand(Light light) {this.light = light;}public void execute() {light.on();}public void undo() {light.off();}
}// 调用者 - 遥控器
public class RemoteControl {private Command command;public void setCommand(Command command) {this.command = command;}public void pressButton() {command.execute();}public void pressUndo() {command.undo();}
}// 使用示例
Light light = new Light();
Command lightOn = new LightOnCommand(light);RemoteControl remote = new RemoteControl();
remote.setCommand(lightOn);
remote.pressButton();  // 开灯
remote.pressUndo();    // 关灯

2. 支持多命令和撤销历史

// 高级遥控器
public class AdvancedRemoteControl {private List<Command> commandHistory = new ArrayList<>();public void executeCommand(Command command) {command.execute();commandHistory.add(command);}public void undoLastCommand() {if (!commandHistory.isEmpty()) {Command lastCommand = commandHistory.remove(commandHistory.size() - 1);lastCommand.undo();}}
}

四、命令模式的应用场景

1. 文本编辑器操作

// 文档类 - 接收者
public class Document {private StringBuilder content = new StringBuilder();public void write(String text) {content.append(text);}public void delete(int length) {if (content.length() >= length) {content.delete(content.length() - length, content.length());}}public String getContent() {return content.toString();}
}// 抽象命令
public interface TextCommand {void execute();void undo();
}// 写入命令
public class WriteCommand implements TextCommand {private Document document;private String text;public WriteCommand(Document document, String text) {this.document = document;this.text = text;}public void execute() {document.write(text);}public void undo() {document.delete(text.length());}
}// 编辑器 - 调用者
public class TextEditor {private List<TextCommand> history = new ArrayList<>();private Document document = new Document();public void executeCommand(TextCommand command) {command.execute();history.add(command);}public void undo() {if (!history.isEmpty()) {TextCommand lastCommand = history.remove(history.size() - 1);lastCommand.undo();}}public void showDocument() {System.out.println("当前文档内容: " + document.getContent());}
}

2. 交易系统

// 交易接收者
public class StockTrade {public void buy(String stock, int shares) {System.out.println("买入 " + shares + " 股 " + stock);}public void sell(String stock, int shares) {System.out.println("卖出 " + shares + " 股 " + stock);}
}// 订单命令接口
public interface Order {void execute();
}// 买入命令
public class BuyOrder implements Order {private StockTrade stockTrade;private String stock;private int shares;public BuyOrder(StockTrade stockTrade, String stock, int shares) {this.stockTrade = stockTrade;this.stock = stock;this.shares = shares;}public void execute() {stockTrade.buy(stock, shares);}
}// 订单处理器 - 调用者
public class OrderProcessor {private List<Order> orders = new ArrayList<>();public void takeOrder(Order order) {orders.add(order);}public void processOrders() {for (Order order : orders) {order.execute();}orders.clear();}
}

3. 智能家居控制

// 设备接口
public interface SmartDevice {void on();void off();
}// 具体设备
public class SmartLight implements SmartDevice {public void on() {System.out.println("智能灯开启");}public void off() {System.out.println("智能灯关闭");}
}// 场景命令
public class SceneCommand implements Command {private List<Command> commands = new ArrayList<>();public void addCommand(Command command) {commands.add(command);}public void execute() {for (Command command : commands) {command.execute();}}public void undo() {for (int i = commands.size() - 1; i >= 0; i--) {commands.get(i).undo();}}
}// 使用场景命令
SceneCommand goodNightScene = new SceneCommand();
goodNightScene.addCommand(new LightOffCommand(livingRoomLight));
goodNightScene.addCommand(new ThermostatSetCommand(thermostat, 20));remote.setCommand(goodNightScene);
remote.pressButton();  // 执行晚安场景

五、命令模式的变体

1. 宏命令（组合命令）

public class MacroCommand implements Command {private Command[] commands;public MacroCommand(Command[] commands) {this.commands = commands;}public void execute() {for (Command command : commands) {command.execute();}}public void undo() {for (int i = commands.length - 1; i >= 0; i--) {commands[i].undo();}}
}

2. 延迟执行命令

public class DelayedCommand implements Command {private Command command;private long delayMillis;public DelayedCommand(Command command, long delayMillis) {this.command = command;this.delayMillis = delayMillis;}public void execute() {new Thread(() -> {try {Thread.sleep(delayMillis);command.execute();} catch (InterruptedException e) {Thread.currentThread().interrupt();}}).start();}
}