为什么 List 中没有 tail() 或 head() 方法来获取最后一个或第一个元素? [英] Why no tail() or head() method in List to get last or first element?

问题描述

我最近和一位同事讨论了为什么 Java 中的 List 接口没有 head() 和 tail() 方法.

I recently had a discussion with a collegue why the List interface in Java doesn't have a head() and tail() method.

为了实现这样的功能，必须编写一个看起来像这样的包装器:

In order to implement such a functionality would have to write a wrapper that looked something like this:

public E head() {
 if (underlyingList == null || underlyingList.isEmpty())
  return null;

 return underlyingList.get(0);
}


public E tail() {
 if (underlyingList == null || underlyingList.isEmpty())
  return null;

 return underlyingList.get(underlyingList.size()-1);
}

我不了解所有 List 实现，但我认为至少在 LinkedList 和 ArrayList 中，获取最后一个和第一个元素(恒定时间)应该非常简单.

I'm not aware of all List implementations but I assume that at least in LinkedList and ArrayList it should be pretty trivial to get the last and first element (constant time).

所以问题是:

为任何 List 实现提供尾部方法不是一个好主意有什么具体原因吗?

Is there a specific reason why it is not a good idea to provide a tail method to any List implementation?

推荐答案

Java Collections Framework 由 Joshua Bloch 编写.他的 API 设计原则之一是:高功率重量比.

Java Collections Framework is written by Joshua Bloch. One of his API design principles is: High power-to-weight ratio.

tail() 和 head() 可以通过 get() 和 size() 实现，所以没有必要将 tail() 和 head() 添加到非常通用的接口 java.util.List 中.一旦用户使用了这些方法，您就没有机会删除它们，您必须永远维护这些不必要的方法.这很糟糕.

tail() and head() can be implemented by get() and size(), so it's not necessary to add tail() and head() to a very general interface java.util.List. Once users use the methods, you don't have chance to remove them and you have to maintain these unnecessary methods forever. That's bad.

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