Thread advanced application-8-JAVA5 thread concurrent collection application and case analysis of collections tool class

1. What are the differences between HashSet and HashMap?

Difference: The former is a single row the latter is a double row, that is, HashMap has a key has a value, hashset only key;

Contact: The bottom of the hashset is HashMap, you can refer to HashSet class source, the default construction method is:

Public HashSet () {

Map = new Hashmap<key,object>

}

is hashset only with the HashMap key, instead of his value, the former value can be arbitrarily assigned by the programmer, anyway

2. The collection in the thread concurrency library is inferior

HashMap and HashSet If the CPU fills up when thousands of threads are concurrent, a collection of new technology concurrent libraries is developed in the JAVA5 thread concurrency library, where the concurrentmap can be used. can also be used in the hashmap of the use of synchronous lock synchronized, in fact, Concurrentmap class is written in the original hashmap to rewrite all the methods, but the return value is the original method plus a synchronous lock

3. Synchronizing Collections

14The following is a case application of a class in a thread concurrent library collection, which is more closely associated with the instructions for changing the knowledge point2  PackageCom.java5.thread.newSkill;3 4 Importjava.util.ArrayList;5 Importjava.util.Collection;6 ImportJava.util.Iterator;7 Importjava.util.concurrent.CopyOnWriteArrayList;8 9  Public classCollectionmodifyexceptiontest {Ten  One     /** A      * @paramargs -      */ -      Public Static voidMain (string[] args) { the  -         //Copyonwritearraylist is a class in the thread concurrency library collection to avoid concurrency exceptions in HashMap -         /* - * Direct use of traditional ArrayList will appear a variety of thread concurrency anomaly, interested can try +          */ -collection<user> users =NewCopyonwritearraylist<user>(); +         //collection<user> users = new arraylist<user> (); AUsers.add (NewUser ("Yangkai", 21)); atUsers.add (NewUser ("Yang Yi", 20)); -Users.add (NewUser ("dashing", 22)); -Iterator itrusers =users.iterator (); -          while(Itrusers.hasnext ()) { -User User =(User) Itrusers.next (); -             if("Chic". Equals (User.getname ())) { in users.remove (user); -}Else { to System.out.println (user); +             } -         } the     } *  $ }Panax Notoginseng  - Helper Class: User class the  PackageCom.java5.thread.newSkill; +  A  Public classUser { the  +     PrivateString name; -     Private intAge ; $User (String name,intAge ) { $         Super(); -          This. Name =name; -          This. Age =Age ; the     } -     Wuyi      PublicString GetName () { the         returnname; -     } Wu  -      Public voidsetName (String name) { About          This. Name =name; $     } -  -      Public intGetage () { -         returnAge ; A     } +  the      Public voidSetage (intAge ) { -          This. Age =Age ; $     } the  the @Override the      Public inthashcode () { the         Final intPrime = 31; -         intresult = 1; inresult = Prime * result +Age ; theresult = Prime * result + ((name = =NULL) ? 0: Name.hashcode ()); the         returnresult; About     } the @Override the      Public Booleanequals (Object obj) { the         if( This==obj) +             return true; -         if(obj = =NULL) the             return false;Bayi         if(GetClass ()! =Obj.getclass ()) the             return false; theUser other =(User) obj; -         if(Age! =other.age) -             return false; the         if(Name = =NULL) { the             if(Other.name! =NULL) the                 return false; the}Else if(!name.equals (other.name)) -             return false; the         return true; the     } the @Override94      PublicString toString () { the         return"User [age=" + Age + ", name=" + name + "]"; the     } the @Override98     protectedObject Clone ()throwsclonenotsupportedexception { About         return Super. Clone (); -     }101     102}

Thread advanced application-8-JAVA5 thread concurrent collection application and case analysis of collections tool class