编程中的智慧之设计模式三

深入探索设计模式：实际应用和优化策略

在前两篇文章中，我们详细探讨了创建型模式、结构型模式、行为模式和架构模式的基本概念及其在Java中的实现。在本文中，我们将进一步探讨如何在实际项目中应用和优化这些模式，尤其是如何在大型系统中灵活运用设计模式，提高系统的扩展性、可维护性和可复用性。

组合模式（Composite Pattern）

组合模式允许你将对象组合成树形结构来表示“整体/部分”层次结构。组合能使客户以一致的方式处理单个对象和组合对象。

import java.util.ArrayList;
import java.util.List;// 组件接口
interface Component {void showDetails();
}// 叶子节点
class Employee implements Component {private String name;private String position;public Employee(String name, String position) {this.name = name;this.position = position;}@Overridepublic void showDetails() {System.out.println(name + " works as " + position);}
}// 组合节点
class Manager implements Component {private String name;private List<Component> subordinates;public Manager(String name) {this.name = name;this.subordinates = new ArrayList<>();}public void addSubordinate(Component component) {subordinates.add(component);}public void removeSubordinate(Component component) {subordinates.remove(component);}@Overridepublic void showDetails() {System.out.println("Manager: " + name);for (Component component : subordinates) {component.showDetails();}}
}// 客户端
public class CompositePatternDemo {public static void main(String[] args) {Employee emp1 = new Employee("John", "Developer");Employee emp2 = new Employee("Jane", "Designer");Manager manager = new Manager("Robert");manager.addSubordinate(emp1);manager.addSubordinate(emp2);manager.showDetails();}
}

中介者模式（Mediator Pattern）

中介者模式定义了一个对象来封装一组对象如何交互。中介者模式促进了松耦合，使得对象不需要显式地相互引用，从而使得它们可以独立变化。

import java.util.ArrayList;
import java.util.List;// 中介者接口
interface Mediator {void sendMessage(String message, Colleague colleague);
}// 具体中介者
class ConcreteMediator implements Mediator {private List<Colleague> colleagues;public ConcreteMediator() {this.colleagues = new ArrayList<>();}public void addColleague(Colleague colleague) {colleagues.add(colleague);}@Overridepublic void sendMessage(String message, Colleague colleague) {for (Colleague c : colleagues) {if (c != colleague) {c.receive(message);}}}
}// 同事类
abstract class Colleague {protected Mediator mediator;public Colleague(Mediator mediator) {this.mediator = mediator;}public abstract void receive(String message);public abstract void send(String message);
}// 具体同事类
class ConcreteColleague1 extends Colleague {public ConcreteColleague1(Mediator mediator) {super(mediator);}@Overridepublic void receive(String message) {System.out.println("Colleague1 received: " + message);}@Overridepublic void send(String message) {System.out.println("Colleague1 sends: " + message);mediator.sendMessage(message, this);}
}class ConcreteColleague2 extends Colleague {public ConcreteColleague2(Mediator mediator) {super(mediator);}@Overridepublic void receive(String message) {System.out.println("Colleague2 received: " + message);}@Overridepublic void send(String message) {System.out.println("Colleague2 sends: " + message);mediator.sendMessage(message, this);}
}// 客户端
public class MediatorPatternDemo {public static void main(String[] args) {Mediator mediator = new ConcreteMediator();Colleague colleague1 = new ConcreteColleague1(mediator);Colleague colleague2 = new ConcreteColleague2(mediator);((ConcreteMediator) mediator).addColleague(colleague1);((ConcreteMediator) mediator).addColleague(colleague2);colleague1.send("Hi, colleague2!");colleague2.send("Hello, colleague1!");}
}

实际项目中的设计模式应用策略

1. 识别模式应用的场景

在实际项目中，识别适当的设计模式应用场景非常重要。开发者需要熟悉不同设计模式的优缺点及其适用场景，以便在特定情况下选择最佳模式。例如，在需要动态改变对象行为时，策略模式（Strategy Pattern）是一种理想的选择；而在需要通过不同方式创建复杂对象时，建造者模式（Builder Pattern）则更为适用。