减少if或switch

减少if或switch

方式一：枚举

public enum Operator {

    ADD {
        @Override
        public int apply(int a, int b) {
            return a + b;
        }
    },

    MUL {
        @Override
        public int apply(int a, int b) {
            return a * b;
        }
    };

    public abstract int apply(int a, int b);

}

方式二：工厂模式

1. 接口

   public interface Operation {
   
       int apply(int a, int b);
   
   }
   

2. 实现

   public class AddOperation implements Operation{
       @Override
       public int apply(int a, int b) {
           return a + b;
       }
   }
   
   public class MultOperation implements Operation{
       @Override
       public int apply(int a, int b) {
           return a * b;
       }
   }
   
   

3. 操作工厂

   public class OperatorHolder {
   
       public static final String OPERATION_ADD = "add";
   
       public static final String OPERATION_MUL = "multiply";
   
       static final Map<String, Operation> operations;
   
       static {
           operations = new HashMap<>(2);
           operations.put(OPERATION_ADD, new AddOperation());
           operations.put(OPERATION_MUL, new MultOperation());
       }
   
       public static int operate(int a, int b, String type) throws Exception{
           Operation operation = operations.get(type);
           if (operation == null){
               throw new IllegalArgumentException("illegal type " + type);
           }
           return operation.apply(a, b);
       }
   
   }
   

方式三：TODO

待补充