Dark Horse Programmer – Java Basic Collection (1) Collection

——Java training, Android training, iOS training, .Net training, looking forward to communicating with you! —— /strong> There are many collections in Java, also called containers. The following figure shows the composition and classification of the collection framework. 1. Why do collection classes appear? Object-oriented languages ​​embody things in the form of objects, so in order to facilitate the operation of multiple objects, objects are stored. Collections are the most commonly used way to store objects. 2. Arrays and collections are both containers. What are the differences? Although arrays can also store objects, their length is fixed; collection lengths are variable. Basic data types can be stored in arrays, while collections can only store objects. 3. Characteristics of collection classes Collections are only used to store objects. The length of the collection is variable, and the collection can store different types of objects. 　　　　　Collection Collection is a common interface in the collection framework. There are two sub-interfaces under it: List and Set. Affiliation: Collection                                                                                                                                                                                                                                               |–List//Elements are ordered and elements can be repeated. Because the collection system has indexes.                      |–Set//The elements are unordered and the elements cannot be repeated. The following is an overview of Collection: 1 import java.util.*; 2…