The TreeSet of Java Learning

Set: Unordered, can not repeat element

|--hashset: The data structure is a hash table, and the thread is non-synchronous.

The principle of guaranteeing element uniqueness: Determining whether the hashcode value of an element is the same

If same, the Equals method of the element will continue to be judged, whether true

|--treeset: You can sort the elements in the Set collection

Note: When sorting, when the main conditions are the same, be sure to judge the secondary condition (otherwise it will be considered the same object without being added)

1 ImportJava.util.Iterator;2 ImportJava.util.TreeSet;3 4 /**5 * Requirements:6 * Store custom objects in TreeSet collection students7 * Want to sort by the age of the students8  */9  Public classPackagedemo {Ten  One      Public Static voidMain (string[] args) { ATreeSet ts=NewTreeSet (); -Ts.add (NewStudent ("Pikachu 1", 20)); -Ts.add (NewStudent ("Pikachu", 20)); theTs.add (NewStudent ("pickup", 19)); -Ts.add (NewStudent ("Racal", 21)); -Ts.add (NewStudent ("Racal", 21)); -          +Iterator it=ts.iterator (); -          +          while(It.hasnext ()) { AStudent student=(Student) It.next (); atSystem.out.println (Student.getname () + "...." +student.getage ()); -         } -          -     } -  - } in classStudentImplementscomparable{//This interface forces students to have a comparative -     PrivateString name; to     Private intAge ; +      PublicStudent (String name,intAge ) { -          This. name=name; the          This. age=Age ; *     } $      PublicString GetName () {Panax Notoginseng         returnname; -     } the      Public intGetage () { +         returnAge ; A     } the @Override +      Public intcompareTo (Object o) { -         if(NULL==o) { $             Throw NewRuntimeException ("Pass in an empty object"); $         } -         if(! (OinstanceofStudent)) { -             Throw NewRuntimeException ("Not in student class"); the         } -Student student=(Student) o;Wuyi         if( This.age>student.age) { the             return1;  -}Else if( This. age==student.age) { Wu             return This.name.compareTo (student.name);///Note: When sorting, when the main conditions are the same, be sure to judge the secondary condition (otherwise it will be considered the same object without being added) -         } About         return-1; $     } -      -      -}

The TreeSet of Java Learning