对简单工厂模式、工厂方法模式的思考

1 背景

题目源自：【设计模式专题之工厂方法模式】2.积木工厂

1.1 题目描述

小明家有两个工厂，一个用于生产圆形积木，一个用于生产方形积木，请你帮他设计一个积木工厂系统，记录积木生产的信息。

1.2 输入描述

输入的第一行是一个整数 N（1 ≤ N ≤ 100），表示生产的次数。
接下来的 N 行，每行输入一个字符串和一个整数，字符串表示积木的类型。积木类型分为 “Circle” 和 “Square” 两种。整数表示该积木生产的数量

1.3 输出描述

对于每个积木，输出一行字符串表示该积木的信息。

1.4 输入示例

3
Circle 1
Square 2
Circle 1

1.5 输出示例

Circle Block
Square Block
Square Block
Circle Block

2 简单工厂模式

• 一个工厂生产多个对象。
  • （1）抽象对象【通过接口进行抽象】
  • （2）具体对象【通过类实现接口】
  • （3）具体工厂
• 代码示例：

public class Main {public static void main(String[] args) {ShapeFactorySystem shapeFactorySystem = new ShapeFactorySystem(new SimpleShapeFactory());Scanner scanner = new Scanner(System.in);int count = Integer.parseInt(scanner.nextLine());for (int i = 0; i < count; i++) {String line = scanner.nextLine();String[] parts = line.split(" ");String type = parts[0];shapeFactorySystem.produce(type, Integer.parseInt(parts[1]));}}
}interface Shape {void draw(int n);
}class Circle implements Shape {public void draw(int n) {for (int i = 0; i < n; i++) {System.out.println("Circle Block");}}
}class Square implements Shape {@Overridepublic void draw(int n) {for (int i = 0; i < n; i++) {System.out.println("Square Block");}}
}class SimpleShapeFactory {public Shape createShape(String type) {if ("Circle".equals(type)) {return new Circle();} else if ("Square".equals(type)) {return new Square();} else {throw new RuntimeException("Unknown type");}}
}class ShapeFactorySystem {private SimpleShapeFactory simpleShapeFactory;public ShapeFactorySystem(SimpleShapeFactory simpleShapeFactory) {this.simpleShapeFactory = simpleShapeFactory;}public void produce(String type, int n) {Shape shape = simpleShapeFactory.createShape(type);shape.draw(n);}
}

3 工厂方法模式

• 和简单工厂不同的是，不同对象的生产工厂也不同。
• 代码示例：

public class Main {public static void main(String[] args) {ShapeFactorySystem shapeFactorySystem = new ShapeFactorySystem(new CircleFactory(), new SquareFactory());Scanner scanner = new Scanner(System.in);int count = Integer.parseInt(scanner.nextLine());for (int i = 0; i < count; i++) {String line = scanner.nextLine();String[] parts = line.split(" ");String type = parts[0];shapeFactorySystem.produce(type, Integer.parseInt(parts[1]));}}
}interface Shape {void draw(int n);
}class Circle implements Shape {public void draw(int n) {for (int i = 0; i < n; i++) {System.out.println("Circle Block");}}
}class Square implements Shape {@Overridepublic void draw(int n) {for (int i = 0; i < n; i++) {System.out.println("Square Block");}}
}interface ShapeFactory {Shape createShape(String type);
}class CircleFactory implements ShapeFactory {@Overridepublic Shape createShape(String type) {return new Circle();}
}class SquareFactory implements ShapeFactory {@Overridepublic Shape createShape(String type) {return new Square();}
}class ShapeFactorySystem {private ShapeFactory circleFactory;private ShapeFactory squareFactory;public ShapeFactorySystem(ShapeFactory circleFactory, ShapeFactory squareFactory) {this.circleFactory = circleFactory;this.squareFactory = squareFactory;}public void produce(String type, int n) {Shape shape;if ("Circle".equals(type)) {shape = circleFactory.createShape(type);} else if ("Square".equals(type)) {shape = squareFactory.createShape(type);} else {throw new RuntimeException("Unknown type");}shape.draw(n);}
}

4 思考

• 从这个例子中，看不出工厂方法模式比简单工厂模式好在哪里。
• 假设需求变化了，需要增加一种类型，那么，对于简单工厂模式，只要修改：

// 新增类
class xxx implements Shape {@Overridepublic void draw(int n) {for (int i = 0; i < n; i++) {System.out.println("xxx Block");}}
}// 修改方法
class SimpleShapeFactory {public Shape createShape(String type) {if ("Circle".equals(type)) {return new Circle();} else if ("Square".equals(type)) {return new Square();} else if (xxx.equals(type)) {...} else {throw new RuntimeException("Unknown type");}}
}

• 但是对应用层代码（main方法）不需要做任何改动。这反而更好。
• 对于简单工厂模式，要修改：

// 修改应用层代码
public static void main(String[] args) {ShapeFactorySystem shapeFactorySystem = new ShapeFactorySystem(new CircleFactory(), new SquareFactory(), xxx);Scanner scanner = new Scanner(System.in);int count = Integer.parseInt(scanner.nextLine());for (int i = 0; i < count; i++) {String line = scanner.nextLine();String[] parts = line.split(" ");String type = parts[0];shapeFactorySystem.produce(type, Integer.parseInt(parts[1]));}
}// 新增类
class xxx implements Shape {@Overridepublic void draw(int n) {for (int i = 0; i < n; i++) {System.out.println("xxx Block");}}
}// 新增类
class xxxFactory implements ShapeFactory {...
}class ShapeFactorySystem {private ShapeFactory circleFactory;private ShapeFactory squareFactory;private xxxFactory ...;public ShapeFactorySystem(ShapeFactory circleFactory, ShapeFactory squareFactory, xxxFactory ...) {this.circleFactory = circleFactory;this.squareFactory = squareFactory;...}public void produce(String type, int n) {Shape shape;if ("Circle".equals(type)) {shape = circleFactory.createShape(type);} else if ("Square".equals(type)) {shape = squareFactory.createShape(type);} else if (xxx) {...} else {throw new RuntimeException("Unknown type");}shape.draw(n);}
}

• 真麻烦啊。

4.1 改进工厂方法模式

• 代码示例：

public class Main {public static void main(String[] args) {ShapeFactorySystem shapeFactorySystem = ShapeFactorySystem.getSingleton();Scanner scanner = new Scanner(System.in);int count = Integer.parseInt(scanner.nextLine());for (int i = 0; i < count; i++) {String line = scanner.nextLine();String[] parts = line.split(" ");String type = parts[0];shapeFactorySystem.produce(type, Integer.parseInt(parts[1]));}}
}interface Shape {void draw(int n);
}class Circle implements Shape {public void draw(int n) {for (int i = 0; i < n; i++) {System.out.println("Circle Block");}}
}class Square implements Shape {@Overridepublic void draw(int n) {for (int i = 0; i < n; i++) {System.out.println("Square Block");}}
}interface ShapeFactory {Shape createShape();
}class CircleFactory implements ShapeFactory {@Overridepublic Shape createShape() {return new Circle();}
}class SquareFactory implements ShapeFactory {@Overridepublic Shape createShape() {return new Square();}
}class ShapeFactorySystem {private static final Map<ShapeType, ShapeFactory> shapeFactoryMap = new HashMap<>();private static ShapeFactorySystem shapeFactorySystem;private ShapeFactorySystem() {shapeFactoryMap.put(ShapeType.CIRCLE, new CircleFactory());shapeFactoryMap.put(ShapeType.SQUARE, new SquareFactory());}public static ShapeFactorySystem getSingleton() {if (shapeFactorySystem == null) {synchronized (ShapeFactorySystem.class) {if (shapeFactorySystem == null) {shapeFactorySystem = new ShapeFactorySystem();}}}return shapeFactorySystem;}private ShapeFactory acquireShapeFactory(ShapeType type) {return shapeFactoryMap.get(type);}public void produce(String type, int n) {ShapeFactory shapeFactory = acquireShapeFactory(ShapeType.of(type));Shape shape = shapeFactory.createShape();shape.draw(n);}
}enum ShapeType {CIRCLE("Circle"), SQUARE("Square");private String value;private ShapeType(String value) {this.value = value;}private String getValue() {return value;}public static ShapeType of(String value) {for (ShapeType shapeType : ShapeType.values()) {if (shapeType.getValue().equals(value)) {return shapeType;}}// 如果没有找到匹配的枚举对象，可以抛出一个异常或返回nullthrow new IllegalArgumentException("Unknown ShapeType: " + value);}
}

多线程场景下，不能用HashMap。

• 如果新增一种类型：

// 新增类
class xxx implements Shape {@Overridepublic void draw(int n) {for (int i = 0; i < n; i++) {System.out.println("xxx Block");}}
}// 新增类
class xxxFactory implements ShapeFactory {@Overridepublic Shape createShape() {return new xxx();}
}// 修改方法（不修改之前代码，新增语句）
private ShapeFactorySystem() {shapeFactoryMap.put(ShapeType.CIRCLE, new CircleFactory());shapeFactoryMap.put(ShapeType.SQUARE, new SquareFactory());
}// 不修改之前的代码，加一个枚举对象
enum ShapeType {CIRCLE("Circle"), SQUARE("Square"), xxx;...
}

• 当然了，通过map + enum这种改进也可以应用到简单工厂模式中。
• 不过，当创建对象变得复杂时，简单工厂模式就难以应用对了：

class SimpleShapeFactory {public Shape createShape(String type) {if ("Circle".equals(type)) {return new Circle(); // 简单对象} else if ("Square".equals(type)) {return new Square(); // 简单对象} else {throw new RuntimeException("Unknown type");}}
}