如何在工厂方法中初始化具有多个参数构造函数的类
假设我有一个计算形状面积的 Shape 接口。我添加了 2 个实现矩形和正方形。我看到的挑战是两种实现都有自己的多参数构造函数。如何使用工厂模式初始化它们。我想用java来解决这个问题。
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));
}
@Override
public int area() {
return length * breadth;
}
}
public class Square implements Shape {
int edge;
public Square(List<String> parameters) {
this.edge = Integer.parseInt(parameters.get(0));
}
@Override
public 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"}));
}
@Override
public Shape make(String shapeType) {
switch (shapeType) {
case "Circle":
return new Square(getParameters(shapeType));
case "Square":
return new Rectangle(getParameters(shapeType));
default:
break;
}
return null;
}
@Override
public List<String> getParameters(String shapeType) {
return shapeInitMap.get(shapeType);
}
}
哆啦的时光机1回答
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潇潇雨雨
您的解决方案不是最佳的，因为：1）您必须为具体的构造函数创建专用的构造函数Shape，并且您失去了参数的类型检查（在编译时）。2）init具体工厂的方法容易出错。这就是我要做的。具体工厂应该携带具体构造函数的参数Shape，但不能作为不确定的字符串（如果从用户输入获取字符串，请在创建具体工厂之前转换它们）：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("..."); } }}客户不需要知道ShapeFactory他正在使用的混凝土，也不必担心Shape他得到的混凝土。依赖关系是相反的：发挥关键作用的是抽象，而不是细节。但如果可能的形状数量增加，您将得到一个具有许多相似参数的构造函数。这是另一个解决方案：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("..."); } }}这更好，因为您不会混合参数：每种混凝土都Shape包含自己的参数。如果你想让它更灵活，你可以使用 Map 将交换机的责任移出具体工厂：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; }}我什至会使用 anenum来代替形状类型而不是字符串，并使用 anEnumMap来处理开关：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(); }}客户端必须知道Shape接口ShapeFactory和ShapeType枚举。“服务器”提供具体ShapeFactoryImpl实例。
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Java