treeset

contentRemark: Details of varchar except ID and parentid This design improves query display efficiency as long as every field is maintained!See the following maintenance Program :-- ===================================================== ===Alter procedure appsp_addnew@ ID integer, @ Title varchar (8000) = NULL, @ Content varchar (8000) = NULLAs-- Declare @ ID int-- Set @ ID = 0If @ ID = 0BeginInsert into tree (parentid, orderid, indent, title, content)Values (0, 0, 0, @ title, @ content)-- Pin t

implemented based on hashmap, which is the fundamental difference between set and list. The hashset storage method uses the key in hashmap as the corresponding storage item of the set. Look at the add (ObjectOBJ.Public Boolean add (Object OBJ){Return map. Put (OBJ, present) = NULL;} This is also the root reason why repeated items cannot be found in the set as in the list, because the key of hashmap cannot be duplicated. Linkedhashset: A subclass of hashset, a linked list.

In Android development, we often need to classify and operate data. For lightweight data storage, we may not need to use SQLite or XML with imperfect efficiency and class libraries, because sharedpreferences does not have the data enumeration method, if it is only a string or Int array, it can be separated by a tag, let's take a look at the introduction of arraylist sorted list set hashmap, an auxiliary class of basic data types provided by Android or Java. If you are familiar with STL or boost

differencesArrayList for thread sync, vector synchronization for thread, multi-select ArrayList in non-multithreaded environment3 Set (element not duplicated)1 TreeSet 1 built-in integer and string types are sorted by natural order and dictionary order, and custom object type ordering requires implementation of the comparable interface Packagecom.fjnu.test;ImportJava.util.Iterator;ImportJava.util.TreeSet; Public classTester { Public Static voidMain

The principle of storage elementsWhen adding elements to HashSet, the Hashcode method of the element is called first to get the hash code value of the element, and then the hash code value is calculated to calculate the position of the element in the hash table.Scenario 1: If the calculated position does not currently have any elements, then the element can be added directly to the hash tableScenario 2: If another element is already present in the calculated position, then the Equals method of

Java container Summary Java containers refer to the List, Set, and Map classes. Due to translation problems, Collection refers to the number of them. List Fast Random Access to ArrayList LinkedList insertion and deletion are fast It is easy to understand that array is an array and random access is fast. Link is a linked list. Of course, it is faster to insert and delete links. Set each element can only be placed once Use Hash TreeSet uses the red/bla

lower. The implementation method is the same as that of ArrayList, but thread security is considered, so the efficiency is slightly lower. --- | Set: No storage order, which cannot be repeated --- | HashSet --- | TreeSet --- | LinkedHashSet --- | Map: Key-Value Pair --- | HashMap --- | TreeMap --- | HashTable --- | LinkedHashMap Why are there so many collection containers? Because each container stores data differently, this storage method is called

I. Implementation of Common collection classes 1. ArrayDeque/shortlist: array and linked list of double-end queues 2. HashSet/Map: Hash 3. TreeSet/Map: red/black tree In fact, TreeSet uses TreeMap internally. When a new element is added, an empty Object is put into the TreeMap as the value. 3.1 When the Comparable and Comparator compare methods are implemented, a positive number indicates that the object o

cases: 1) It can be passed to a sorting method, such as Collections. sort () or Arrays. sort (), to precisely control the sorting method. 2) It can also be used to control the sorting of specific data structures, such as TreeSet or TreeMap. For example, to create a TreeSet, we can pass a comparator to its constructor or implement the comparable interface. Implementation 1 (using comparator) class Dog {int

: fast access speed.HashSet the principle of storing elements:When adding elements to HashSet, the Hashcode method of the element is called to get the hash code value of the element, and then the hash code value is calculated to calculate the position of the element in the hash table.Scenario 1: If the calculated position does not currently have any elements, then the element can be added directly to the hash table.Scenario 2: If the calculated position already has other elements, then the Equal

the HashSet class accesses the object according to the hash algorithm, and when a new object is added to the collection, the object's Hashcode () method is called to get the object's hash code, and then the location of the object stored in the collection is computed based on the code. The Hashcode () method is actually the physical address of the returned object store.So in general, HashSet is judged by the two-element Hashcode () method and the Equals () method to determine whether the two ele

allowed to be duplicated, plus a single original element, or just one.Linkedhashsetclass uses a list implementation to extend the HashSet class, which supports elements within the rule setSort(in the order they were inserted)Note:If you do not need to maintain the order in which elements are inserted, you should use HashSet, which is more efficient than linkedhashset.TreeSetclass implements the specific class Navigableset class of SortedSet, which can be added to a

. The Linkedhashset performance is better than hashset when iterating through all the elements in the set, but the performance is slightly inferior to hashset at insert time. The TreeSet class TreeSet is the only implementation class for the SortedSet interface, and TreeSet ensures that the collection element is in the sorted state.

element, but the elements in the HashSet set must overwrite the equals () and hashcode () methods, while the TreeSet set class stores the elements in it in order. HashSet stores elements in a set based on the hash algorithm, and uses the hash algorithm to improve access efficiency. Features of a HashSet set: 1. the arrangement order of elements cannot be guaranteed. The order of elements in the set may change at any time. A maximum of three null elem

togetherTo traverse a set collection: 1. Change the collection to an array, 2. Iterate through iterators (unordered: The order of addition is different from the order printed)Treeset: Sorts elements using the self-heating order of the elements, using a two-fork tree for the underlyingTreeSet Use note points:1. When adding objects to TreeSet, if the object has this naturally ordered attribute, sort by this

Describe:Given an array of integers, let you find the smallest number of k from the arrayIdeas:The simplest and most brutal way is to sort the array and take the first number of K. However, the only thing required is to find the smallest number of k, with the sort can be but a little wasted, such as the 10,000 integer array of the smallest 10 numbers, the average time to sort the complexity of the difference is Nlog (N).So think of, with the heap to achieve, but oneself realize and too troubleso

[Java class set] _ notes for sorting and repeating Elements Objectives of this chapter: Master the sorting principle of treesetUnderstanding the definition of repeated elements in the Set Interface 3. Details: The contents of the treeset class can be sorted, so now I will give a class at will to see if it can be sorted. Import Java. util. set; import Java. util. treeset; class person {private string name; p

Hashset needs to override equals and hashcode Treeset needs to override equals and compareto The results returned by the two functions must be consistent. In general, hashset and treeset only put immutable objects, and final modifies attributes. New comparator () {public int compare (Object O1, object O2 ){...... } The Anonymous class can be used as a treeset