对象的泛型下界

本文介绍了对象的泛型下界的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 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 docs.oracle/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 docs.oracle/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.