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This article introduces the relevant knowledge of "what are the characteristics of the Java collection container". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

I. introduction to collection containers

Collection container is the most basic API module in Java development, which is usually used to store dynamically created elements at run time. The basic features are as follows:

Generic features that store objects of any type

Dynamic expansion to store any number of objects

The amount of storage here is constrained by environments such as programs and memory, and as you can see from List's get () method, the scope of index is Integer.MAX_VALUE.

II. API system

Three core interfaces: List, Set inherit Collection, Map independent interface

List and Set system

API:ArrayList,LinkedList, Vector, the core of List system

Core of Set system: API:HashSet, TreeSet, LinkedHashSet

Queue queues API:PriorityQueue, LinkedHashSet

Map system

Core of Map system: API:HashMap, LinkedHashMap, TreeMap, Hashtable

3. Detailed explanation of basic container 1. Core content

Basic usage such as element storage, addition, deletion, modification, search, etc.

Thread safety problems in API method

Container initialization size and dynamic expansion mechanism

Characteristics of underlying data structure

Comparison of containers with the same interface or different interface systems

Basically proficient in using and understanding collection containers, you need to know the following: basic usage of API, thread safety issues; container size and expansion; structural features, arrays, linked lists, hash tables

2. Detailed explanation of API system.

Collection: the root interface of the collection container, defining public methods

List system:

ArrayList

Maintain Object array implementation, features: fast query, slow addition and deletion, non-thread-safe, so high efficiency.

LinkedList

Low-level maintenance linked list data structure implementation, features: slow query, fast additions and deletions, non-thread safety, so high efficiency.

Vector

The bottom maintains the Object array, the implementation is the same as ArrayList, but Vector is thread-safe and inefficient.

Set system:

HashSet

The underlying layer is supported by a hash table, which is characterized by fast access, unique and unordered elements.

LinkedHashSet

The underlying data structure is linked list and hash table, the linked list ensures the order of elements, and the hash table ensures element uniqueness and non-thread safety.

TreeSet

The data structure is a red-black tree, and if the elements have the characteristics of natural order, they are sorted according to the properties of the natural order of the elements, or custom sorting based on the comparator.

Map system:

The implementation class of the Map interface has the characteristics: the stored data is in the way of key-value pairs, the key can not be repeated, the value can be repeated.

HashMap

The underlying hashCode table is used to add elements to the HashMap. Null values and null keys are allowed, and the order of the elements is not guaranteed.

TreeMap

TreeMap: based on the data structure of binary tree, the keys with natural characteristics are sorted and stored: the keys of elements are sorted and stored directly; without natural characteristics, the Comparable interface is implemented and the sorting rules are defined in ComparaTo.

HashTable

Thread-safe, relatively inefficient, null values are not allowed.

3. Container traversal

Process control based on for, foreach and while

Iterable iterator core interface

Lambda expressions: traversing, grouping, querying

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