How TreeMap and TreeSet compare elements when sorting, how the sort () method in the Collections tool class compares elements

TreeSet and TreeMap sorting when comparing elements require element objects to implement comparable interfaces

There are two ways to compare elements in the collections sort method:

Element object implementation comparable interface

Entity class Dog

1  Public classDogImplementsCloneable,comparable<dog> {2 3     PrivateString name;4     PrivateString age;5     6      PublicString GetName () {7         returnname;8     }9      Public voidsetName (String name) {Ten          This. Name =name; One     } A      PublicString getage () { -         returnAge ; -     } the      Public voidsetage (String age) { -          This. Age =Age ; -     } -      PublicDog (string name, String age) { +         Super(); -          This. Name =name; +          This. Age =Age ; A     } at      PublicDog () { -         Super(); -     } - @Override -      PublicString toString () { -         return"Dog [name=" + name + ", age=" + Age + "]"; in     } -      to      PublicObject Clone ()throwsclonenotsupportedexception { +          -         return Super. Clone (); the     } * @Override $      Public intcompareTo (Dog o) {Panax Notoginseng          -         return  This. GetName (). CompareTo (O.getname ()); the     } +}

Test class

1  Public classTest {2 3      Public Static voidMain (string[] args) {4list<dog> list =NewArraylist<dog>();5Dog D1 =NewDog ("CAC", "11");6Dog D2 =NewDog ("BAC", "11");7Dog D3 =NewDog ("AAC", "11");8Dog D4 =NewDog ("EAC", "11");9 List.add (d1);Ten List.add (D2); One List.add (D3); A List.add (D4); - //Mycompare mc = new Mycompare (); - //Collections.sort (LIST,MC); the Collections.sort (list); -          for(Dog dog:list) { - System.out.println (dog); -         } +          -     } +}

Results:

Dog [NAME=AAC, age=11]
Dog [Name=bac, age=11]
Dog [NAME=CAC, age=11]
Dog [Name=eac, age=11]

Custom comparer, Collections.sort (List list,comparator<t> Compare), creating a comparator class implementation interface

1  Public classTest {2 3      Public Static voidMain (string[] args) {4list<dog> list =NewArraylist<dog>();5Dog D1 =NewDog ("CAC", "11");6Dog D2 =NewDog ("BAC", "11");7Dog D3 =NewDog ("AAC", "11");8Dog D4 =NewDog ("EAC", "11");9 List.add (d1);Ten List.add (D2); One List.add (D3); A List.add (D4); -Mycompare MC =NewMycompare (); - Collections.sort (LIST,MC); the          for(Dog dog:list) { - System.out.println (dog); -         } -          +     } - } +  A classMycompareImplementsComparator<dog>{ at  - @Override -      Public intCompare (dog D1, dog D2) { -String S1 =d1.getname (); -String s2 =d2.getname (); -         if(s1.equals (S2)) in             return0; -         Else { to             returnS1.compareto (S2); +         } -     } the  *}

Results:

Dog [NAME=AAC, age=11]
Dog [Name=bac, age=11]
Dog [NAME=CAC, age=11]
Dog [Name=eac, age=11]

How TreeMap and TreeSet compare elements when sorting, how the sort () method in the Collections tool class compares elements