Inferring a generic type from a generic type in Java (compile time error) -

i have static function following signature generic type t

public static<t> list<t> sortmap(map<t, comparable> map) 

which should return list of map keys property.

now want pass generic hashmap of type s

map<s,double> map 

in calling static function within generic class, has map member variable.

i have listed minimal code example below.

however, error message (s , t both t's in different scopes of code, i.e. t#1 = t, t#2= s):

  required: map<t#1,comparable>   found: map<t#2,double>   reason: cannot infer type-variable(s) t#1   (argument mismatch; map<t#2,double> cannot converted map<t#1,comparable>) 

how can resolve issue? surprised java not allow inferring generic type generic type. structure in java can 1 use work kind of more abstract code reasoning?

code:

public class exampleclass<t> {     map<t, double> map;     public exampleclass () {         this.map = new hashmap();     }     //the following line produces mentioned error     list<t> sortedmapkeys = utilitymethods.sortmap(map); }  public class utilitymethods {      public static<t> list<t> sortmap(map<t, comparable> map) {         // sort map in way , return list      } } 

it's not problem t , s, comparable , double.

the reason error map<t, double> not map<t, comparable>.

you'll have widen bit scope of second type-parameter. like:

public static <t, s extends comparable<s>> list<t> function(map<t, s> map) {     //implementation } 

then, you'll able invoke method with:

map<s, double> map = new hashmap<s, double>(); function(map);