Java Basic Knowledge Hardening Collection Framework note 43:set Collection TreeSet stores an integer type of element and traverses

1. TreeSet class overview:

• ability to sort elements according to a certain rule.

• or sort according to the comparator provided when the set was created

• Depending on the construction method used

2. code example:

1  Packagecn.itcast_05;2 3 ImportJava.util.TreeSet;4 5 /*6 * TreeSet: Ability to sort elements according to a certain rule. 7 * There are two ways of sorting8 * A: Natural sort9 * B: Comparator sortTen  *  One * Features of the TreeSet collection: sort and unique  A  *  - * by observing TreeSet's Add () method , we know that we will eventually look at the put () method of TreeMap .  -  */ the  Public classTreesetdemo { -      Public Static voidMain (string[] args) { -         //To create a collection object -         //sort in natural order +treeset<integer> ts =NewTreeset<integer>(); -  +         //Create elements and add A         //20,18,23,22,17,24,19,18,24 atTs.add (20); -Ts.add (18); -Ts.add (23); -Ts.add (22); -Ts.add (17); -Ts.add (24); inTs.add (19); -Ts.add (18); toTs.add (24); +  -         //Traverse the          for(Integer i:ts) { * System.out.println (i); $         }Panax Notoginseng     } -}

Run the effect as follows:

3. TreeseT guarantees the source parsing of the ordering of elements :

By observing the Add () method of TreeSet, we know that we will eventually look at the put () method of TreeMap.

1 InterfaceCollection {...}2 3 InterfaceSetextendsCollection {...}4 5 InterfaceNavigablemap {6 7 }8 9 classTreeMapImplementsNavigablemap {Ten       Publicv put (K key, V value) { OneEntry<k,v> T =Root; A         if(T = =NULL) { -Compare (key, key);//type (and possibly null) check -  theRoot =NewEntry<> (key, value,NULL); -Size = 1; -modcount++; -             return NULL; +         } -         intCMP; +Entry<k,v>parent; A         //split comparator and comparable paths atcomparator<?Superk> CPR =Comparator; -         if(CPR! =NULL) { -              Do { -Parent =T; -CMP =Cpr.compare (key, T.key); -                 if(CMP < 0) int =T.left; -                 Else if(CMP > 0) tot =T.right; +                 Else -                     returnT.setvalue (value); the} while(t! =NULL); *         } $         Else {Panax Notoginseng             if(Key = =NULL) -                 Throw Newnullpointerexception (); thecomparable<?Superk> k = (comparable<?SuperK>) key; +              Do { AParent =T; theCMP =K.compareto (t.key); +                 if(CMP < 0) -t =T.left; $                 Else if(CMP > 0) $t =T.right; -                 Else -                     returnT.setvalue (value); the} while(t! =NULL); -         }WuyiEntry<k,v> e =NewEntry<>(key, value, parent); the         if(CMP < 0) -Parent.left =e; Wu         Else -Parent.right =e; About fixafterinsertion (e); $size++; -modcount++; -         return NULL; -     } A } +  the classTreeSetImplementsSet { -     Private transientNavigablemap<e,object>m; $      the      PublicTreeSet () { the           This(NewTreemap<e,object>()); the     } the  -      Public BooleanAdd (e e) { in         returnM.put (e, PRESENT) = =NULL; the     } the}

The real comparison is dependent on the CompareTo () method of the element, and this method is defined in the comparable. So, if you want to rewrite the method, you must first comparable the interface. This interface represents a natural sort.

Java Basic Knowledge Hardening Collection Framework note 43:set Collection TreeSet stores an integer type of element and traverses