什么是java集合？ [英] What is a java collection?

问题描述

我想知道：Java中的集合是什么？

I want to know: What is a collection in Java?

推荐答案

通常是 java.util.Collection （虽然 java.util.Map 正式也是集合框架的一部分）

Usually an instance of java.util.Collection (although java.util.Map is officially also a part of the collections framework)

虽然Collection接口可以直接实现，但通常客户端代码将使用一个子接口的实现：设置，列表，队列 / Deque

Although the Collection interface can be implemented directly, usually client code will use an implementation of one of the sub interfaces: Set, List, Queue / Deque

下面是一些示例代码（左侧）通常见界面，右侧有一个实现类）。

Here is some sample code (on the left side you will usually see an interface and on the right side an implementation class).

集合不存储重复项，其所有元素都是唯一的：

Sets don't store duplicates, all of their elements are unique:

final Set<String> basicSet = new HashSet<String>();
basicSet.add("One");
basicSet.add("Two");
basicSet.add("One");
basicSet.add("Three");
System.out.println(basicSet.toString());
// Output: [Three, One, Two]
// (seemingly random order, no duplicates)

SortedSets 是以特定顺序存储元素的集合的特殊情况：

SortedSets are a special case of sets that store elements in a specified order:

final SortedSet<String> sortedSet = new TreeSet<String>();
sortedSet.add("One");
sortedSet.add("Two");
sortedSet.add("One");
sortedSet.add("Three");
System.out.println(sortedSet.toString());
// Output: [One, Three, Two]
// (natural order, no duplicates)

列表让您多次存储值并访问或修改插入顺序：

Lists let you store a value multiple times and access or modify insertion order:

final List<String> strings = new ArrayList<String>();
strings.add("Two");
strings.add("Three");
strings.add(0, "One");
strings.add(3, "One");
strings.add("Three");
strings.add(strings.size() - 1, "Two");
System.out.println(strings);
// Output: [One, Two, Three, One, Two, Three]

还有用于定义列表的实际速记：

There is also a practical shorthand for defining a list:

List<String> strings = Arrays.asList("One", "Two", "Three");
// this returns a different kind of list but you usually don't need to know that

等。

要更好地了解，请阅读来自Sun Java教程（在线）的Collections Trail ，或 Java通用和收藏 by Maurice Naftalin和Philip Wadler

To get a better understanding, read The Collections Trail from the Sun Java Tutorial (online), or Java Generics and Collections by Maurice Naftalin and Philip Wadler

这篇关于什么是java集合？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！