目录
- Lesson: Introduction to Collections
Lesson: Introduction to Collections
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.
简单地来说，集合(有时叫做容器)就是一个把多个元素组合进一个单个单元的对象。集合通常用于存储、提取，操作和传递聚合数据。Typically, they represent data items that form a natural group, 例如一手扑克(一个卡片的集合)，一封邮件(一个字母的集合)，或者一个电话簿(一个姓名到电话的映射)。如果你已经使用过java百年城语言或者任何其他的语言，那么你应该是已经熟悉集合。
What Is a Collections Framework?
何为集合框架
A collections framework is a unified architecture for representing and manipulating collections. All collections frameworks contain the following:
所有集合框架包括如下：
- 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 implement collection interfaces. The algorithms are said to be polymorphic: that is, the same method can be used on many different implementations of the appropriate collection interface. In essence, algorithms are reusable functionality.
Apart from the Java Collections Framework, the best-known examples of collections frameworks are the C++ Standard Template Library (STL) and Smalltalk’s collection hierarchy. Historically, collections frameworks have been quite complex, which gave them a reputation for having a steep learning curve. We believe that the Java Collections Framework breaks with this tradition, as you will learn for yourself in this chapter.
Benefits of the Java Collections Framework Java集合框架的优点
The Java Collections Framework provides the following benefits:
Java集合框架提供了如下有点：
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.
降低变成的难度：
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.
提升编程的速度和质量：
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.
允许不相关的API之间可相互操作：
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.
减少学习和使用新的API的工作量：
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.
减少设计新的API的工作量：
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.
促进软件重用：
