如何通过反射减少IF-ELSE的使用？我可以得到代码示例 [英] How to reduce the usage of IF - ELSE by reflection ? Can I get the code example

问题描述

我正在尝试使用PizzaFactory Class的代码，以便我可以删除if else条件，使我的代码更具动态性。但是我不能弄清楚如何。

  Pizza.java 
包PizzaTrail; 
 import java.util.List; 
 
 //这是将由具体工厂扩展的主要抽象工厂
 public abstract class Pizza {public abstract List fetchIngredients（String Type）; 
 
 
 PizzaFactory.java 
包PizzaTrail; 
 import java.util.List; 
 
 //这是具体的工厂
 public class PizzaFactory extends Pizza 
 {
 public static Pizza getConcretePizza（String PType）
 {
披萨p = null; 
 if（PType.equals（Cheese））
 {
 p = new CheesePizza（）; 
} else if（PType.equals（Pepperoni））
 {
 p = new PepperoniPizza（）; 
} 
 else if（PType.equals（Clam））
 {
 p = new CalmPizza（）; 
 
} 
 else if（PType.equals（Veggie））
 {
 p = new VeggiePizza（）; 
 
} 
 return（p）; 
} 
} 
 
 
 ChessePizza.java 
包PizzaTrail; 
 
 import java.util.ArrayList; 
 import java.util.List; 
 
 public class CheesePizza extends Pizza {
列表ing = new ArrayList（）; 
 @Override 
 public List fetchIngredients（String Type）
 {
 ing.add（Ingredient：Shredded Mozzarella Cheese）; 
 ing.add（Ingredient：Peppers）; 
 ing.add（Ingredate：Feta cheese）; 
 ing.add（Ingredinator：Pesto）; 
 return（ing）; 
} 
 
} 
 
} 
  

任何人都可以帮我找到在pizzaFactory类中使用的反射，以便我可以动态调用类CheesePizza等。

解决方案

为了在减少if-else使用方面回答您的问题，您可以动态地确定要使用的类例如而不是

  if（PType.equals（Cheese））{
 p = new CheesePizza（）; 
  

您可以使用

  Class.forName（PType +Pizza）。newInstance（）; //可能需要一个包
  

（上面假设一个无参数构造函数）

，这样会删除任何切换类型的行为。

然而，我不会推荐这个。以上是很难调试的，不明显的。您的IDE可能会将这些类别标记为未被使用，并且可能会在未来的重构器中被删除。简单来说，我宁愿通过if / else序列指定可用的比萨饼的规格，一个基于字符串的切换，字符串到方法对象的映射等，而不是任何复杂的，不明显的，也许是脆弱的机制。

I was trying to use reflection for the code of PizzaFactory Class so that I can remove the if else condition and make my code more dynamic. But I am not able to figure out how.

   Pizza.java
    package PizzaTrail;
   import java.util.List;

    //this is the main abstract factory which will be extended by the concrete factory 
    public abstract class Pizza {  public abstract List fetchIngredients(String Type); }


    PizzaFactory.java 
   package PizzaTrail;
   import java.util.List;

   //this is the concrete factory 
   public class PizzaFactory extends Pizza
   { 
        public static Pizza getConcretePizza(String PType)
        { 
          Pizza p=null;
          if (PType.equals("Cheese")) 
          {
                     p=new CheesePizza();
          } else if (PType.equals("Pepperoni")) 
          {
              p=new PepperoniPizza();
          }
           else if (PType.equals("Clam")) 
          {
               p = new CalmPizza();

           }
           else if (PType.equals("Veggie")) 
           {
               p= new VeggiePizza();

            }
            return(p); 
       }   
   }


     ChessePizza.java
     package PizzaTrail;

      import java.util.ArrayList;
      import java.util.List;

     public class CheesePizza extends Pizza {
      List ing = new ArrayList();
       @Override
       public List fetchIngredients(String Type)
       {
       ing.add("Ingredient : Shredded Mozzarella Cheese");
      ing.add("Ingredient : Peppers");
      ing.add("Ingredient : Feta cheese");
     ing.add("Ingredient : Pesto");
      return (ing);   
      }

    }

  }

Can anyone help me get the reflection used in the pizzaFactory class so that i can call the class CheesePizza, etc dynamically?

解决方案

To answer your question in terms of reducing 'if-else' usage, you could dynamically determine the class to use e.g. instead of

if (PType.equals("Cheese")) {
    p=new CheesePizza();

you could use

Class.forName(PType + "Pizza").newInstance(); // might need a package

(the above assumes a no-args constructor)

and that would remove any switching-type behaviour.

However I wouldn't recommend this. The above is difficult to debug and non-obvious. Your IDE will likely mark such classes as not being used and a possible candidate for removal during a future refactor. I would favour clarity in the vast majority of cases.

In short, I would much rather specify the specifications of available pizzas via an if/else sequence, a String-based switch, a map of strings to method objects etc. rather than any convoluted, non-obvious, perhaps fragile mechanism.

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