为什么 Java Collection Framework 不包含 Tree 和 Graph [英] Why Java Collection Framework doesn't contain Tree and Graph

问题描述

我熟悉 Java Collection Framework，它包含基本接口:Collection 和 Map.我想知道为什么框架不包含作为基本集合的树和图的结构.两者都可以看作是Collection的子类型.

I am familiar with Java Collection Framework which contains basic interfaces: Collection and Map. I am wondering why the Framework doesn't contain structures as Tree and Graph which are basic collections. Both can be regarded as sub types of Collection.

顺便说一下，我知道TreeSet 是由红黑树底层实现的.但是，TreeSet 不是 Tree 而是 Set，因此框架中没有真正的 Tree.

By the way, I know TreeSet is implemented by Red-Black Tree underlying. However, the TreeSet is not a Tree but a Set, so there's no real Tree in the framework.

推荐答案

我想知道为什么框架不包含作为基本集合的树和图的结构.两者都可以看作是Collection的子类型.

这是个好问题.我认为这可以归结为范围界定.Collections API 提供的类的核心功能是:

This is a good question. I think it simply boils down to scoping. The core features that Collections API provides classes for are:

• 迭代顺序:列表和排序映射有指定的迭代顺序，大多数集合没有.

• iteration order: Lists and sorted maps have specified iteration order, most sets don't.

duplicates:列表允许重复，集合不允许

duplicates: Lists allow duplicates, sets do not

index:列表值由整数索引，地图值由其他对象索引.

index: List values are indexed by integers, map values are indexed by other objects.

这让我们走得很远，我认为 Joshua Bloch 等人认为可以在顶部实现更多功能丰富的集合(需要元素之间的内部关系的图和树、具有多重性的集合、双向映射等)这三个核心功能中的一部分，因此在库中效果更好.

This gets us very far and I assume Joshua Bloch et al argued that more feature rich collections (graphs and trees which require internal relationship between elements, sets with multiplicity, bi-directional maps, ...) can be implemented on top of these three core features, and are thus better off in libraries.

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