假設我有一個計算形狀面積的 Shape 接口。我添加了 2 個實現矩形和正方形。我看到的挑戰是兩種實現都有自己的多參數構造函數。如何使用工廠模式初始化它們。我想用java來解決這個問題。public class Rectangle implements Shape {int length;int breadth;public Rectangle(List<String> parameters) { this.length = Integer.parseInt(parameters.get(0)); this.breadth = Integer.parseInt(parameters.get(1));}@Overridepublic int area() { return length * breadth;}}public class Square implements Shape {int edge;public Square(List<String> parameters) { this.edge = Integer.parseInt(parameters.get(0));}@Overridepublic int area() { return edge * edge;}}public interface Shape {int area();}public interface ShapeFactory {public Shape make(String shapeType);public List<String> getParameters(String shapeType);}public class ShapeFactoryImpl implements ShapeFactory {Map<String, List<String>> shapeInitMap = new HashMap<>();public void init(){ shapeInitMap.put("Circle", Arrays.asList(new String[]{"4"})); shapeInitMap.put("Rectangle", Arrays.asList(new String[]{"2","3"}));}@Overridepublic Shape make(String shapeType) { switch (shapeType) { case "Circle": return new Square(getParameters(shapeType)); case "Square": return new Rectangle(getParameters(shapeType)); default: break; } return null;}@Overridepublic List<String> getParameters(String shapeType) { return shapeInitMap.get(shapeType);}}
1 回答
瀟瀟雨雨
TA貢獻1833條經驗 獲得超4個贊
您的解決方案不是最佳的，因為：1）您必須為具體的構造函數創建專用的構造函數Shape，并且您失去了參數的類型檢查（在編譯時）。2）init具體工廠的方法容易出錯。
這就是我要做的。具體工廠應該攜帶具體構造函數的參數Shape，但不能作為不確定的字符串（如果從用戶輸入獲取字符串，請在創建具體工廠之前轉換它們）：
public interface ShapeFactory {
public Shape make(String shapeType);
}
public class ShapeFactoryImpl implements ShapeFactory {
private int circleRadius;
private int rectangleLength;
private int rectangleBreadth;
public ShapeFactoryImpl(int circleRadius, int rectangleLength, int rectangleBreadth){
this.circleRadius = circleRadius;
this.rectangleLength = rectangleLength;
this.rectangleBreadth = rectangleBreadth;
}
public Shape make(String shapeType) {
switch (shapeType) {
case "Circle": return new Circle(this.circleRadius);
case "Rectangle": return new Rectangle(this.rectangleLength, this.rectangleBreadth);
default: throw new Exception("...");
}
}
}
客戶不需要知道ShapeFactory他正在使用的混凝土，也不必擔心Shape他得到的混凝土。依賴關系是相反的：發揮關鍵作用的是抽象，而不是細節。但如果可能的形狀數量增加，您將得到一個具有許多相似參數的構造函數。這是另一個解決方案：
public class ShapeFactoryImpl implements ShapeFactory {
private Shape circle;
private Shape rectangle;
public ShapeFactoryImpl(Circle circle, Rectangle rectangle){
this.circle = circle;
this.rectangle = rectangle;
}
public Shape make(String shapeType) {
switch (shapeType) {
case "Circle": return this.circle.clone();
case "Rectangle": return this.rectangle.clone();
default: throw new Exception("...");
}
}
}
這更好，因為您不會混合參數：每種混凝土都Shape包含自己的參數。如果你想讓它更靈活，你可以使用 Map 將交換機的責任移出具體工廠：
public class ShapeFactoryImpl implements ShapeFactory {
private Map<String, Shape> shapeByType;
public ShapeFactoryImpl(Map<String, Shape> shapeByType){
this.shapeByType = shapeByType;
}
public Shape make(String shapeType) {
Shape shape = this.shapeByType.get(Type).clone();
if (shape == null) {
throw new Exception("...");
}
return shape;
}
}
我什至會使用 anenum來代替形狀類型而不是字符串，并使用 anEnumMap來處理開關：
public class ShapeFactoryImpl implements ShapeFactory {
private EnumMap<ShapeType, Shape> shapeByType;
public ShapeFactoryImpl(Map<ShapeType, Shape> shapeByType){
this.shapeByType = shapeByType;
}
public Shape make(ShapeType shapeType) {
return this.shapeByType.get(Type).clone();
}
}
客戶端必須知道Shape接口ShapeFactory和ShapeType枚舉?！胺掌鳌碧峁┚唧wShapeFactoryImpl實例。
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