语法< T extends Class< T>>在Java中 [英] The syntax <T extends Class<T>> in Java

问题描述

我对以下内容有一些想法：

  public interface MaxStack< T extends Comparable< T>> 
  

<1>为什么实现 MaxStack 应该这样写：



  public class MaxStackclass< T extends Comparable< T>>实施MaxStack< T> 
  

而不是 public class MaxStackclass< T extends Comparable< T>>实现MaxStack< T扩展Comparable< T>> ？





2-为什么这个类的私有变量使用泛型，只能写成< T> ，而不是< code>< T extnds Comparable< T>> ？例如，私人列表< T> stack = new ArrayList< T>（）;

<3> < T extends Comparable< ; T>> 和< T扩展Comparable> - 如果我需要比较类中的元素，编辑：我认为3的问题在于它可能允许插入一个以第二种方式定义的列表，使其具有不同的元素，这些元素都是从可比，然后当我想比较它们时，这是不可能的，因为我们无法将字符串与Integer进行比较，都是从Comparable扩展而来。 解决方案

1. 在声明 maxStackclass< T extends Comparable< T>> 在 T 上。所以你不需要它。




2. 原因与上面相同。
   

3. < T extends Comparable< T>> 意味着 T 必须实现 Comparable 接口，它可以比较两个 T 实例。 < T扩展Comparable> 意味着 T implements Comparable 这样它就可以比较两个 Object 。如果我需要比较我班中的元素，那么我们就可以比较一下这些元素。

，两者都可以，
不可以？



嗯，技术上你可以 使用两者的结果。但是对于声明< T extends Comparable> ，它将涉及不必要的转换，您可以避免使用类型安全的< T extends Comparable< T> >




I have couple of thoughts regarding the following:

public interface MaxStack<T extends Comparable <T>>

1-Why does the class that implements MaxStack should be written like this:

public class MaxStackclass<T extends Comparable <T>> implements MaxStack<T>

and not public class MaxStackclass<T extends Comparable <T>> implements MaxStack<T extends Comparable <T>>?

2- why do the private variables of this class, when I use generics, should be written only with <T> and not with <T extnds Comparable<T>>? For example, private List<T> stack= new ArrayList<T>();

3-What is the difference between <T extends Comparable<T>> and <T extends Comparable>- if I need to compare bewteen elements in my class, both will be O.K, no?

Edit: I think that thee problem with 3 is that maybe it allows to insert of a list that was defined in the second way to have different elements which all extends from comparable and then when I want to compare them, it won't be possible, since we can't compare String to Integer, both extend from Comparable.

解决方案

1. In the declaration maxStackclass<T extends Comparable <T>> you have already expressed the bounds on T. So you do not need it again.

2. Reason same as above. No need to specify bounds on the same type parameter again.

3. <T extends Comparable<T>> means that T must implement the Comparable interface that can compare two T instances. While <T extends Comparable> means T implements Comparable such that it can compare two Objects in general. The former is more specific.

if I need to compare bewteen elements in my class, both will be O.K, no?

Well, technically you can achieve the same result using both. But for the declaration <T extends Comparable> it will involve unnecessary casts which you can avoid using the type safe <T extends Comparable<T>>

这篇关于语法&lt; T extends Class&lt; T&gt;&gt;在Java中的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！