Java Basic Knowledge Hardening Collection Framework note 57:map Collection HashMap collection (hashmap<student,string>) case

Source: Internet
Author: User

1. Case of HashMap Collection (hashmap<student,string>)

Hashmap<student,string>
Key: Student
Requirement: If the member variable values for two objects are the same, then the same object.
Value: String

HashMap is the most commonly used map collection, and its key-value pairs are stored with the hash code of the key to determine where the value is placed.

An object that is a key in HashMap must override the Hashcode () method of object and the Equals () method

2. code example:

(1)Student. Java, as follows:

1  Packagecn.itcast_02;2 3  Public classStudent {4     PrivateString name;5     Private intAge ;6 7      PublicStudent () {8         Super();9     }Ten  One      PublicStudent (String name,intAge ) { A         Super(); -          This. Name =name; -          This. Age =Age ; the     } -  -      PublicString GetName () { -         returnname; +     } -  +      Public voidsetName (String name) { A          This. Name =name; at     } -  -      Public intGetage () { -         returnAge ; -     } -  in      Public voidSetage (intAge ) { -          This. Age =Age ; to     } +  - @Override the      Public inthashcode () { *         Final intPrime = 31; $         intresult = 1;Panax Notoginsengresult = Prime * result +Age ; -result = Prime * result + ((name = =NULL) ? 0: Name.hashcode ()); the         returnresult; +     } A  the @Override +      Public Booleanequals (Object obj) { -         if( This==obj) $             return true; $         if(obj = =NULL) -             return false; -         if(GetClass ()! =Obj.getclass ()) the             return false; -Student other =(Student) obj;Wuyi         if(Age! =other.age) the             return false; -         if(Name = =NULL) { Wu             if(Other.name! =NULL) -                 return false; About}Else if(!name.equals (other.name)) $             return false; -         return true; -     } -  A}

(2) test class HashMapDemo4, as follows:

1  Packagecn.itcast_02;2 3 ImportJava.util.HashMap;4 ImportJava.util.Set;5 6 /*7 * hashmap<student,string>8 * Key: Student9 * Requirements: If the member variable values for two objects are the same, then the same object . Ten * Value: String One  */ A  Public classHashMapDemo4 { -      Public Static voidMain (string[] args) { -         //To create a collection object theHashmap<student, string> HM =NewHashmap<student, string>(); -  -         //Create student Objects -Student S1 =NewStudent ("Marten Cicada", 27); +Student s2 =NewStudent ("Wang Zhaojun", 30); -Student s3 =NewStudent ("Xi Shi", 33); +Student S4 =NewStudent ("Yang Yuhuan", 35); AStudent S5 =NewStudent ("Marten Cicada", 27); at  -         //adding elements -Hm.put (S1, "8888"); -Hm.put (S2, "6666"); -Hm.put (S3, "5555"); -Hm.put (S4, "7777"); inHm.put (S5, "9999"); -  to         //Traverse +Set<student> set =Hm.keyset (); -          for(Student key:set) { theString value =Hm.get (key); *System.out.println (Key.getname () + "---" + key.getage () + "---" $+value);Panax Notoginseng         } -     } the}

Run the results as follows:

Student as the key object, overriding object's Hashcode () method and the Equals () method, (code as above), rerun the result as follows :

Java Basic Knowledge Hardening Collection Framework note 57:map Collection HashMap collection (hashmap<student,string>) case

Related Article

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.