对象的泛型下界 [英] Generic lower bound to Object

问题描述

可以将一个泛型参数绑定为：

  public< T super Object> void someMethod（T t）; 
  

是否有这样一个绑定的有效用法？

解决方案

根据JLS http://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.4 类型参数（< T

  TypeParameter：
 TypeVariable TypeBound * 
 
 TypeBound：
 extends TypeVariable 
 extends ClassOrInterfaceType AdditionalBoundList * 
 
 AdditionalBoundList：
 AdditionalBound AdditionalBoundList 
 AdditionalBound 
 
 AdditionalBound：
&接口类型
  

* =可选

TypeBound ，仅指定 extends 的用法。
不幸的是，未指定使用 super 的下限类型参数。下限仅在通配符用法中指定（ JLS＃4.5.1 ）

好的问题，让我在JLS中挖掘，我不知道为什么没有实现在java中，它只是没有指定。

It is possible to code a generic parameter bound as:

public <T super Object> void someMethod(T t);

Is there a valid usage of such a bound?

解决方案

According to the JLS http://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.4 a type parameter (The < T extends Object > term) consists out of:

TypeParameter:
    TypeVariable TypeBound*

TypeBound:
    extends TypeVariable
    extends ClassOrInterfaceType AdditionalBoundList*

AdditionalBoundList:
    AdditionalBound AdditionalBoundList
    AdditionalBound

AdditionalBound:
    & InterfaceType

* = optional

You see the TypeBound, there is only the usage of extends specified. Unfortunately, a lower bound type parameter, using super, is not specified. A lower bound is only specified in the wildcard usage (JLS#4.5.1)

Good question, that got me digging in the JLS, and I don't know why this not implemented in java, it is just not specified.

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