Java 将对象转换为 ArrayList<String>
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cast object to ArrayList<String>
提问by padre
is it possible to cast an Objectto e.g. ArrayList<String>
是否可以将 an 转换Object为例如ArrayList<String>
the code below gives an example of the problem. The Problem is in the last row
下面的代码给出了问题的一个例子。问题在最后一行
setDocs((ArrayList<Document>)obj);
where I want to cast an Object objto ArrayList<String>
在这里我想投一个Object obj，以ArrayList<String>
public void setValue(Object obj)
{
if(obj instanceof TFile)
setTFile((TFile)obj);
else
if(obj instanceof File)
setFile((File)obj));
else
if(obj instanceof Document)
setDoc((Document)obj);
else
if(obj instanceof ArrayList)
setDocs((ArrayList<Document>)obj);
}
采纳答案by Guillaume
In Java generics are not reified, i.e. their generic type is not used when casting.
在 Java 中，泛型没有具体化，即在转换时不使用它们的泛型类型。
So this code
所以这段代码
setDocs((ArrayList<Document>)obj);
will be executed as
将被执行为
setDocs((ArrayList)obj);
As that runtime cast won't check your ArrayListcontains Documentobjects, the compiler raises a warning.
由于该运行时强制转换不会检查您的ArrayListcontainsDocument对象，因此编译器会发出警告。
回答by Thilo
No, that is not possible due to how generics are implemented in Java.
不，这是不可能的，因为泛型在 Java 中是如何实现的。
The type information is not available at runtime, so it cannot be checked by instanceof.
类型信息在运行时不可用，因此无法通过instanceof.
What you can do is cast to Listand then check each element if it is a Documentor not.
您可以做的是强制转换为List然后检查每个元素是否为 a Document。
