Map Study Notes

Collection is a single-column collection, and map is a double-row collection. It contains the <k,v> key-value pairs, note that the keys are unique and the values are not unique.

Here are three ways to read: Keyset,valueset, and EntrySet.

Keyset is the collection that gets all the keys. Valueset is to get all worthwhile collections. EntrySet is a collection of all entries, and entry is the meaning of each entry (the key and the value).

The specific usage is:

1  PackageJavastudy;2 3 Importjava.util.Collection;4 ImportJava.util.HashMap;5 ImportJava.util.Iterator;6 ImportJava.util.Map.Entry;7 ImportJava.util.Set;8 9  Public classTextmap {Ten      Public Static voidMain (String args[]) One     { A         //Create a HashMap array (note: Because the map type is a key-value pair, and the type is worth a larger initial) -         //hashmap<float, string> hp =new hashmap<float,string> (); -hashmap<string,string> HP =NewHashmap<string,string>(); the         //use the put definition to map out the actual keys and values -Hp.put ("010", "Beijing"); -Hp.put ("021", "Shanghai"); -Hp.put ("022", "Chongqing"); +Hp.put ("023", "Tianjin"); -         //traversing prints its array +         //get a collection of all keys ASet<string> sd=Hp.keyset (); atIterator<string> zips=sd.iterator (); -           while(Zips.hasnext ()) -          { -              //get the key value -String zip=Zips.next (); -              //because the key value is unique, the value is obtained from each key, the key is unique, and the value is not unique.  inString cityname=hp.get (Zip); -System.out.println (zip+ ":" +cityname); to          } +         //values get all worthwhile collections -Collection<string> cs=hp.values (); theIterator<string> it =cs.iterator (); *           while(It.hasnext ()) $          {Panax Notoginseng System.out.println (It.next ()); -          } the  +         //EntrySet is printed to get all entries, entry= one line, meaning of an entry; ASet<entry<string, string>> se=Hp.entryset (); theIterator<entry<string, string>> ie=se.iterator (); +           while(Ie.hasnext ()) -          { $              //The key is unique, the value is not unique; Getkey is the collection of keys, GetValue gets all the worth of the collection; $Entry<string, string> es=Ie.next (); -System.out.println (Es.getkey () + ":" +Es.getvalue ()); -          } the           -     }Wuyi  the}

Also try to use a custom concept to create a sort of set of classes for the comparator and its people, specifically (if you have questions, refer to the previous chapter for a specific introduction):

1  PackageJavastudy;2 3 ImportJava.util.Comparator;4 ImportJava.util.Iterator;5 ImportJava.util.Map.Entry;6 ImportJava.util.Set;7 ImportJava.util.TreeMap;8 9  Public classTexttree {Ten  One      Public Static voidMain (string[] args) { A         //TODO auto-generated Method Stub -Treemap<people,people> tm=NewTreemap<people,people> (NewMyComp ());  -Tm.put (NewPeople ("Mark", 12),NewPeople ("Jine", 19)); theTm.put (NewPeople ("Keven", 16),NewPeople ("Bob", 20)); -Set<entry<people,people>> SE =Tm.entryset (); -Iterator<entry<people, people>> is=se.iterator (); -          while(Is.hasnext ()) +         { -Entry<people, people>es=Is.next (); +System.out.println (Es.getkey () + "\ T" +Es.getvalue ()); A         } at     } - } - classMyCompImplementsComparator<people> - { -  - @Override in      Public intCompare (People O1, people O2) { -         //TODO auto-generated Method Stub to         returnO1.name.compareTo (o2.name); +     } -      the }  * classpeople $ {Panax Notoginseng String name; -     intAge ; thePeople (String name,intAge ) +     { A          This. name=name; the          This. age=Age ; +     } -     voidShow () $     { $System.out.println (String.Format ("Name =%s, age =%d", Name,age)); -     } - @Override the      PublicString toString () { -         return"Name=" + name + ", age=" +Age ;Wuyi     } the}

Map Study Notes