Java - 定义扩展类A并实现接口B的成员 [英] Java - Defining a member that extends class A and implements interface B

问题描述

我有一个必须满足两个条件的变量，我想在定义中设置它们。我知道我可以用单个变量定义任一条件，像以上任何一个例子一样

  private Class <？延伸A>变量; //或
私有变量; //或
私人类<？扩展B>变量; //或
私有B变量; 
  

但是有没有办法让变量满足两个条件？

我希望得到类似的东西

  private Class <？扩展A实现B>变量; 
  

但是当我需要调用它或存储时，我找不到任何可以不使用类型转换的方法它的多个副本

解决方案

您可以声明具有多个边界的类型参数，例如：

  public static< T extends A& B个void test（Class< T> clazz）
  

但是你不能声明一个具有多个边界的变量： / p>

 私人类<？扩展A& B个变量; //不起作用
  

您可以创建 abstract class C ，它扩展了 A 并实现了 B ，所以只需要一个边界。

 抽象类C扩展A implements B {} 
  
 
 $ b $ p 
 
 
 
 
 
 $ b $私人类< ？扩展C>变量; 
  

I have a variable that must meet two conditions, and I want to set them in the definition

I know that I can define either condition with an individual variable, like in any of these examples

private Class<? extends A> variable; //or
private A variable; //or
private Class<? extends B> variable; //or
private B variable;

But is there a way to have the variable meet both conditions?

I was hoping for something like this

private Class<? extends A implements B> variable;

But I can't find any way to do this without typecasting when I need to call it or storing multiple copies of it

解决方案

You can declare type parameters that have multiple bounds, such as:

public static <T extends A & B> void test(Class<T> clazz)

But you cannot declare a variable that has multiple bounds:

private Class<? extends A & B> variable;  // doesn't work

You can create an abstract class C that extends A and implements B, so that only one bound is required.

abstract class C extends A implements B {}

Then:

private Class<? extends C> variable;

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