Java Generics Casting between Interfaces -

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i have question according casting when generics in java used. tried provide small example explains problem.

ivariable.java

public interface ivariable { } 

iproblem.java

public interface iproblem<v extends ivariable> { } 

algorithm.java

public class algorithm<v extends ivariable, p extends iproblem<v>> {      public void dosomething(p problem) {          // error: type mismatch: cannot convert p iproblem<ivariable>         iproblem<ivariable> genericproblem = problem;      }  } 

why need cast variable genericproblem explicitly

@suppresswarnings("unchecked") iproblem<ivariable> genericproblem = (iproblem<ivariable>) problem; 

and warning?

the method has p argument of type iproblem because v has implement ivariable well. mistake? workaround?

i not want write

iproblem<v> genericproblem = problem; 

because input variable of problem might different. anyway in opinion iproblem<v> more specific iproblem<ivariable>.

thanks in advance!

an iproblem<v> not equivalent iproblem<ivariable>, if v constrainted ivariable, because java's generics invariant. sure, iproblem<v> way go, if don't want that, can use upper-bounded wildcard express relationship between v , ivariable instead:

iproblem<? extends ivariable> genericproblem = problem;