目錄
- 1 背景
- 1.1 題目描述
- 1.2 輸入描述
- 1.3 輸出描述
- 1.4 輸入示例
- 1.5 輸出示例
- 2 簡單工廠模式
- 3 工廠方法模式
- 4 思考
- 4.1 改進工廠方法模式
1 背景
題目源自：【設計模式專題之工廠方法模式】2.積木工廠
1.1 題目描述
小明家有兩個工廠，一個用于生產圓形積木，一個用于生產方形積木，請你幫他設計一個積木工廠系統，記錄積木生產的信息。
1.2 輸入描述
輸入的第一行是一個整數 N（1 ≤ N ≤ 100），表示生產的次數。
接下來的 N 行，每行輸入一個字符串和一個整數，字符串表示積木的類型。積木類型分為 “Circle” 和 “Square” 兩種。整數表示該積木生產的數量
1.3 輸出描述
對于每個積木，輸出一行字符串表示該積木的信息。
1.4 輸入示例
3
Circle 1
Square 2
Circle 1
1.5 輸出示例
Circle Block
Square Block
Square Block
Circle Block
2 簡單工廠模式
- 一個工廠生產多個對象。
- （1）抽象對象【通過接口進行抽象】
- （2）具體對象【通過類實現接口】
- （3）具體工廠
- 代碼示例：
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 工廠方法模式
- 和簡單工廠不同的是，不同對象的生產工廠也不同。
- 代碼示例：
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
- 從這個例子中，看不出工廠方法模式比簡單工廠模式好在哪里。
- 假設需求變化了，需要增加一種類型，那么，對于簡單工廠模式，只要修改：
// 新增類
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");}}
}
- 但是對應用層代碼（main方法）不需要做任何改動。這反而更好。
- 對于簡單工廠模式，要修改：
// 修改應用層代碼
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]));}
}// 新增類
class xxx implements Shape {@Overridepublic void draw(int n) {for (int i = 0; i < n; i++) {System.out.println("xxx Block");}}
}// 新增類
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);}
}
- 真麻煩啊。
4.1 改進工廠方法模式
- 代碼示例：
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;}}// 如果沒有找到匹配的枚舉對象，可以拋出一個異常或返回nullthrow new IllegalArgumentException("Unknown ShapeType: " + value);}
}
多線程場景下，不能用HashMap。
- 如果新增一種類型：
// 新增類
class xxx implements Shape {@Overridepublic void draw(int n) {for (int i = 0; i < n; i++) {System.out.println("xxx Block");}}
}// 新增類
class xxxFactory implements ShapeFactory {@Overridepublic Shape createShape() {return new xxx();}
}// 修改方法（不修改之前代碼，新增語句）
private ShapeFactorySystem() {shapeFactoryMap.put(ShapeType.CIRCLE, new CircleFactory());shapeFactoryMap.put(ShapeType.SQUARE, new SquareFactory());
}// 不修改之前的代碼，加一個枚舉對象
enum ShapeType {CIRCLE("Circle"), SQUARE("Square"), xxx;...
}
- 當然了，通過map + enum這種改進也可以應用到簡單工廠模式中。
- 不過，當創建對象變得復雜時，簡單工廠模式就難以應用對了：
class SimpleShapeFactory {public Shape createShape(String type) {if ("Circle".equals(type)) {return new Circle(); // 簡單對象} else if ("Square".equals(type)) {return new Square(); // 簡單對象} else {throw new RuntimeException("Unknown type");}}
}
)
)
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