java - Priority Queue Sorting String -

i need use priorityqueue sort person objects.

the person class:

    public class person implements comparable<person>{     private string firstname;     private string lastname;      public person(string firstname, string lastname){        this.firstname = firstname;        this.lastname = lastname;     }      public string getfirstname() {return firstname;}      public string getlastname() {return lastname;}      public string tostring(){        return "name: " + firstname + " " + lastname + "\n";     }      public int compareto(person p){        string pname1 = firstname + lastname;        string pname2 = p.firstname + p.lastname;        return pname1.compareto(pname2);     } 

the main code:

    import java.util.priorityqueue;      public class priorityq{         public static void main(string[] args){            priorityqueue<person> pers = new priorityqueue<person>();            pers.add(new person("sam", "smith"));            pers.add(new person("charlie", "black"));            pers.add(new person("betty", "brown"));            pers.add(new person("jessica", "stewart"));            pers.add(new person("john", "friday"));            pers.add(new person("frank", "folcy"));            system.out.print(pers);              }        } 

i need to:

1. print without sort (already done in main)
2. sort last name
3. sort first name, last name

i must not change code in person class.

i created new class:

    import java.util.comparator;     public class lastnamecomparator implements comparator<person>{        public int compareto(person a, person b){          person p1 = (person)a;          person p2 = (person)b;          if(p1.getlastname().equals(p2.getlastname()))          {             return p1.getfirstname().compareto(p2.getfirstname());          }          return p1.getlastname().compareto(p2.getlastname());        }     } 

it has compile error:

lastnamecomparator.java:2: error: lastnamecomparator not abstract , not override abstract method compare(person,person) in comparator 

first have remove comparable interface person class , implementations: try this:

import java.util.comparator;     public class lastnamecomparator implements comparator<person>{         @override     public int compare(person o1, person o2) {          return o1.lastname.compareto(o2.lastname);     }     } 

and in main method following sort last name:

collections.sort(pers,new lastnamecomparator());     iterator<person> = pers.iterator();     while(it.hasnext()){         system.out.println(it.next());        }