sorting - Error for Collections.sort using Comparable, Java -

first-timer here, having problem here java code: import java.util.*;

public class pootis { public static void main(string[] args) {        superhero batman = new superhero("bruce", 26, "batman");     human rachel = new human("rachel", 24);     superhero ironman = new superhero("tony", 35, "ironman");     human pepper = new human("pepper", 22);        list<human> people = new arraylist<>();     people.add(batman);     people.add(rachel);     people.add(ironman);     people.add(pepper);      collections.sort(people);//<-----     } } 

the purpose of program sort people in people arraylist age. using comparable interface this. problem appears when collections.sort(people) called. did wrong?? second class:

public class human implements comparable<human> { private int age; private string name;  public human(string givenname, int age) {     this.name = givenname;     this.age = age; } @override public int compareto(human other){     if(getage() > other.getage()){         return 1;     }     else if(getage() < other.getage()){         return -1;     }     return 0; }   public string getname() {     return name; }  public int getage() {     return age; }   } 

this error:

pootis.java:65: error: no suitable method found sort(list) collections.sort(people); ^ method collections.sort(list,comparator) not applicable (cannot instantiate arguments because actual , formal argument lists differ in length) method collections.sort(list) not applicable (inferred type not conform declared bound(s) inferred: object bound(s): comparable) t#1,t#2 type-variables: t#1 extends object declared in method sort(list,comparator) t#2 extends comparable declared in method sort(list) 1 error

this superhero class:

public class superhero { string alterego, name; int age;  public superhero(string givenname, int age, string alterego) {     super();     this.alterego = alterego;     this.name = givenname;     this.age = age; }  public string getalterego() {     return alterego; } public string introduce() {     return "hey! i'm " + name + " , i'm " + age + " years old. i'm known as" + alterego + "!"; } } 

the signature of collections.sort() is:

public static <t extends comparable<? super t>> void sort(list<t> list) 

this means can call sort on list of comparable objects. using list<object> not valid object not comparable. sort() overloaded

public static <t> void sort(list<t> list,                         comparator<? super t> c) 

but not applicable method call you've provided 1 parameter.

bear in mind that, per javadoc, in order sort list using collections.sort() elements must mutually comparable. in case means should have way of comparing human superhero. also, if superhero extends human, list should declared list<human> (or viceversa).