构造函数的条件调用

Question

我的情况类似于 this。

如果我仍然想有条件地调用构造函数怎么办？（虽然他们说创建单独的 classes 是可取的）

需求结构：

超级class:

 public class Super
    {
        public Super(DTO1 dto1Object){
               this.dto1Object = dto1Object;     
          }

        public Super(DTO2 dto2Object)){
               this.dto2Object = dto2Object;     
          }
    }

派生class:

 public class Derived extends Super
    {
        public Derived(Object obj)
        {
           //some_condition to check if passed object obj is dto1Object                 
           //do something with dto1Object

           //some_condition to check if passed object is dto2Object                               
           //do something with dto2Object


        }
    }

我该如何实施？

编辑：

根据以下建议以这种方式实现：

超级class:

 public class Super
    {
        protected static DTO1 dto1Obj;
        protected static DTO2 dto2Obj;

        public Super(DTO1 dto1Object){
               this.dto1Object = dto1Object;     
          }

        public Super(DTO2 dto2Object)){
               this.dto2Object = dto2Object;     
          }
    }

派生class:

    public class Derived extends Super
    {
        public Derived(DTO1 dto1Object){ super(dto1Object); }
        public Derived(DTO2 dto2Object){ super(dto2Object); }

        public static Derived create(Object obj) {

           if (obj.equals(dto1Obj) {
             return new Derived((DTO1) obj);
           }

           if (obj.equals(dto2Obj) {
             return new Derived((DTO2) obj);
           }

           // ...

          private String Function(String str){
            if(create(dto1Obj).equals(dto1Obj) { 
             //do something
            }
            else if(create(dto2Obj).equals(dto2Obj)){
             //do something else 
            }
            return str;
          }

        }
    }

编辑2：

根据下面的建议，这是使用 instanceof 的正确方法吗？

if (create(dto1Obj) instanceof DTO1) {
          //something
        }
        else if(create(dto2Obj) instanceof DTO2) {
          //something else
        }

显示以下错误：

Incompatible conditional operand types Derived and DTO1
Incompatible conditional operand types Derived and DTO2

Answer 1

你不能在构造函数中，因为 super(...) 必须是第一个语句。

我能想到的唯一方法是使用静态工厂方法，并调用构造函数的 class 特定重载：

public class Derived extends Super
{
    private Derived(DTO1 dto1Object){ super(dto1Object); }
    private Derived(DTO2 dto2Object){ super(dto2Object); }

    public static Derived create(Object obj) {
       //some_condition to check if passed object obj is dto1Object                 
       //do something with dto1Object
       if (someCondition) {
         return new Derived((DTO1) obj);
       }

       //some_condition to check if passed object is dto2Object                               
       //do something with dto2Object
       if (someOtherCondition) {
         return new Derived((DTO2) obj);
       }

       // ...?
    }
}

构造函数的条件调用

Conditional calling of a constructor

java

constructor

instanceof

constructor-overloading