集合简介

集合的概念，在 Java 的官方文档中，是这样描述的：

A collection — sometimes called a container — is simply an object that groups multiple elements into a single unit. Collections are used to store, retrieve, manipulate, and communicate aggregate data. Typically, they represent data items that form a natural group, such as a poker hand (a collection of cards), a mail folder (a collection of letters), or a telephone directory (a mapping of names to phone numbers). If you have used the Java programming language — or just about any other programming language — you are already familiar with collections.

可以简单理解为：

• 集合(容器)：是将多个元素分组到一个单元中的对象。
• 集合：用于存储、检索、操作和通信聚合数据。

集合框架

关于集合框架，这样说道：

A collections framework is a unified architecture for representing and manipulating collections. All collections frameworks contain the following:

• Interfaces: These are abstract data types that represent collections. Interfaces allow collections to be manipulated independently of the details of their representation. In object-oriented languages, interfaces generally form a hierarchy.
• Implementations: These are the concrete implementations of the collection interfaces. In essence, they are reusable data structures.
• Algorithms: These are the methods that perform useful computations, such as searching and sorting, on objects that implemen

介绍了集合框架和集合狂的组成：

• 集合框架：用于表示和操作集合的统一体系结构
• 集合框架由三部分组成：接口、实现、算法

集合框架的好处

The Java Collections Framework provides the following benefits:

• Reduces programming effort: By providing useful data structures and algorithms, the Collections Framework frees you to concentrate on the important parts of your program rather than on the low-level "plumbing" required to make it work. By facilitating interoperability among unrelated APIs, the Java Collections Framework frees you from writing adapter objects or conversion code to connect APIs.
• Increases program speed and quality: This Collections Framework provides high-performance, high-quality implementations of useful data structures and algorithms. The various implementations of each interface are interchangeable, so programs can be easily tuned by switching collection implementations. Because you're freed from the drudgery of writing your own data structures, you'll have more time to devote to improving programs' quality and performance.
• Allows interoperability among unrelated APIs: The collection interfaces are the vernacular by which APIs pass collections back and forth. If my network administration API furnishes a collection of node names and if your GUI toolkit expects a collection of column headings, our APIs will interoperate seamlessly, even though they were written independently.
• Reduces effort to learn and to use new APIs: Many APIs naturally take collections on input and furnish them as output. In the past, each such API had a small sub-API devoted to manipulating its collections. There was little consistency among these ad hoc collections sub-APIs, so you had to learn each one from scratch, and it was easy to make mistakes when using them. With the advent of standard collection interfaces, the problem went away.
• Reduces effort to design new APIs: This is the flip side of the previous advantage. Designers and implementers don't have to reinvent the wheel each time they create an API that relies on collections; instead, they can use standard collection interfaces.
• Fosters software reuse: New data structures that conform to the standard collection interfaces are by nature reusable. The same goes for new algorithms that operate on objects that implement these interfaces.

描述了集合框架带来的好处，大概就是这样了：

• 减少编程工作
• 提高程序速度和质量
• 允许不相关api之间的互操作性
• 减少了学习和使用新api的工作量
• 减少了设计新api的工作量
• 促进软件重用

更多参考：Introduction to Collections (The Java™ Tutorials > Collections)