工厂模式

定义一个创建对象的接口，让其子类自己决定实例化哪一个工厂类，工厂模式使其创建过程延迟到子类进行，它提供了一种创建对象的最佳方式。

public interface Shape {
   void draw();
}

public class Rectangle implements Shape {

   @Override
   public void draw() {
      System.out.println("Inside Rectangle::draw() method.");
   }
}

public class Square implements Shape {

   @Override
   public void draw() {
      System.out.println("Inside Square::draw() method.");
   }
}

public class ShapeFactory {
    
   //使用 getShape 方法获取形状类型的对象
   public Shape getShape(String shapeType){
      if(shapeType == null){
         return null;
      }        
      if(shapeType.equalsIgnoreCase("CIRCLE")){
         return new Circle();
      } else if(shapeType.equalsIgnoreCase("RECTANGLE")){
         return new Rectangle();
      } else if(shapeType.equalsIgnoreCase("SQUARE")){
         return new Square();
      }
      return null;
   }
}

public class FactoryPatternDemo {

   public static void main(String[] args) {
      ShapeFactory shapeFactory = new ShapeFactory();

      //获取 Circle 的对象，并调用它的 draw 方法
      Shape shape1 = shapeFactory.getShape("CIRCLE");

      //调用 Circle 的 draw 方法
      shape1.draw();

      //获取 Rectangle 的对象，并调用它的 draw 方法
      Shape shape2 = shapeFactory.getShape("RECTANGLE");

      //调用 Rectangle 的 draw 方法
      shape2.draw();

      //获取 Square 的对象，并调用它的 draw 方法
      Shape shape3 = shapeFactory.getShape("SQUARE");

      //调用 Square 的 draw 方法
      shape3.draw();
   }
}

//完善
public class ShapeFactory {
    public static Object getClass(Class<?extends Shape> clazz) {
        Object obj = null;

        try {
            obj = Class.forName(clazz.getName()).newInstance();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }

        return obj;
    }
}

Rectangle rect = (Rectangle) ShapeFactory.getClass(Rectangle.class);
rect.draw();
Square square = (Square) ShapeFactory.getClass(Square.class);
square.draw();

//进阶
public class ShapeFactory {
    public static <T> T getClass(Class<? extends T> clazz) {
        T obj = null;

        try {
            obj = (T) Class.forName(clazz.getName()).newInstance();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }

        return obj;
    }
}

Rectangle rect = ShapeFactory.getClass(Rectangle.class);
rect.draw();

Shape square = ShapeFactory.getClass(Square.class);
square.draw();