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

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