<> aggregate

​ Java Set is java A toolkit is provided , All inherited from java.util.*. It mainly includes two interfaces Collection Interface and Map Interface and related tool classes (
Iterator Iterator Interface ,Enumeration Enumeration class ,Arrays and Colletions).

(1)Collection It's an interface , contain List List and Set aggregate . among List It's an orderly queue , Element values can be repeated , Index from 0 start , The implementation classes are LinkedList,
ArrayList,Vector; and Set Is a collection that does not allow duplicate elements ,Set The implementation classes of HashSet and TreeSet.HashSet Rely on HashMap
, It's actually through the HashMap Realized ;TreeSet Rely on TreeMap, It's actually through the TreeMap Realized .
(2)Map Is a mapping interface , adopt key-value Key value pair implementation . The implementation classes are HashMap,TreeMap,WeakHashMap,Hashtable.
(3)Iterator Is a tool for traversing collections ,Enumeration It's also a traversal collection , But it's more functional than that Iterator less , Only in Hashtable, Vector,
Stack Use in .
(4)Arrays and `Collections Is an operation array , Two tool classes of the collection .

Here is a more specific comparison :
(1) ArrayList, LinkedList, Vector, Stack yes List Of 4 Implementation classes , Compare their similarities and differences .

1)ArrayList Is an array queue , Equivalent to a dynamic array . It is implemented by an array , High efficiency of random access , Random insertion , The efficiency of random deletion is low . The default size is 10 element

2)LinkedList It's a two-way linked list . It can also be used as a stack , Queue or double ended queue for operation .LinkedList Low efficiency of random access , But randomly inserted , High efficiency of random deletion .

3)Vector It's a vector queue , and ArrayList equally , It is also a dynamic array , Implemented by array . however ArrayList It's not thread safe , and Vector It's thread safe .

4)Stack It's a stack , It inherits from Vector. Its characteristics are : First in, second out (FILO, First In Last Out).

(2)HashMap,HashTable,TreeMap The difference between

1)HashMap It is stored in the form of key value pairs , But there is no guarantee of order , Single thread ; Default size 16, The default expansion factor is 0.75,
structure 1.7 before ( array + Linked list ),1.8 after ( array + Linked list + Red and black trees )

HashMap stay JDK1.8 And later versions introduced the structure of red black tree , If the number of linked list elements in the bucket is greater than or equal to 8 Time , Converting linked list into tree structure ; If the number of linked list elements in the bucket is less than or equal to 6 Time , Tree structure reduced to linked list . Because the average search length of red and black trees is log(n), Count Reg 8 When , The average search length is 3, If you continue to use the linked list , The average search length is 8/2=4, This is necessary to convert to a tree . If the list length is less than or equal to 6,6/2=3, Although the speed is also very fast , But the time to convert to tree structure and spanning tree is not too short .

There are also options 6 and 8, There's a difference in the middle 7 It can effectively prevent frequent conversion of linked list and tree . Suppose , If the number of linked lists exceeds 8 Then the linked list is converted into a tree structure , The number of linked lists is less than 8 Then the tree structure is converted into a linked list , If one HashMap Constantly inserting , Delete element , The number of linked lists is in 8 Wandering left and right , It will happen frequently , Linked list to tree , It's going to be inefficient .

2)HashTable And HashMap The storage method is the same , But it's thread safe ;

3)TreeMap Is an ordered key value pair , Sorting based on red black tree .

©2019-2020 Toolsou All rights reserved,
SQL Server Database Glossary CSS Animation effect dedecms Website is hacked How to solve hijacking to other websites Count the number of letters (java Language implementation )Java Basics ( Three ) String In depth analysis The difference between static method and non static method And storage location Django Personal blog building tutorial --- Time classified archiving Keras Save and load model (JSON+HDF5)hive Summary of processing methods for a large number of small files Website mobile phone number capture method