Java泛型和泛型类型 [英] Java Generics and generic types

问题描述

我有一个类ExtA，它包含一个过滤器函数来过滤一个ArrayList：

I have a class ExtA which contains a filter function to filter an ArrayList:

public ExtA<T> filt(...)
{

 //code


}

当我编译它时给我错误：无法找到符号类T.为什么这样？

when I compile it is giving me error: cannot find symbol- class T. Why is this?

推荐答案

你必须告诉它，在这种情况下，T是一个泛型类型：

You have to tell it, that T is a generic type in this case:

public <T> ExtA<T> filt(Func<T, Boolean> a)

您使用符号 T ，但该符号仅在接口声明本身中有效。你在方法中使用的 T 是一个不同的 T 。您必须再次声明它，因为该方法未在接口声明中实现。

You declared your interface with the symbol T, but that symbol is only valid in the interface declaration itself. The T you are using in your method is a different T. You have to declare it again, since the method is not implemented inside the interface declaration.

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