将派生类转换为父类时，是否会丢失数据？ [英] When casting a derived class to a parent class do you lose data?

问题描述

例如

public class parentClass{
     //stuff done
 }

public class derivedClass extends parentClass{
    // has data that parentClass does not
}

// some function 
public parentClass foo(parentClass myVar){
    return myVar
}

// ... later ...

{
  ...
   derivedClass dClass1 = new derivedClass();

   parentClass pClass = foo(dClass1);

   derivedClass dClass2 = (derivedClass)pClass;
 ...
}

dClass1和dClass2之间的数据丢失了吗？我不确定，我认为答案是否定的。我知道如果我使用双打和整数然后数据丢失，但这不是使用指针和对象，所以我不确定。

Was data lost between dClass1 and dClass2? I am not sure, I think the answer is no. I know that if I was using doubles and ints then data IS lost, but that isn't using pointers and objects, so I wasn't sure.

推荐答案

您无法投射对象，因此无法丢失数据。您所能做的就是将引用转换为对象，这不会以任何方式改变它。

You cant cast objects so you can't lose data. All you can do is cast the reference to an object and this doesn't alter it in any way.

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