What is the type of the list being returned?

Consider the following piece of code:

class Test{
  static <T> List<T> lstOf(T ...values){
      List<T> lst = new ArrayList<T>(values.length);
      for ( T val : values)
          lst.add(val);
      return lst;
  }

    static class Obj<T>{
        T value;
        public Obj(T val){
            this.value = val;
        }
    }

    public static void main(String [] args){
        Obj<Integer> intVal = new Obj<Integer>(22);
        Obj<Long> longVal = new Obj<Long>(22L);
        List<Obj<? extends Number>> lst = lstOf(intVal, longVal);
    }
}

The compiler complains that "lst" is of type

java.util.List<Test.Obj<? extends java.lang.Number&java.lang.Comparable<? extends java.lang.Number&java.lang.Com开发者_运维知识库parable<?>>>>

What is the type of the list object returned by lstOf method? How do I successfully assign a type to the returned value?

The inferred type is List<Test.Obj<? extends Number & Comparable<? extends Number & Comparable<?>>>> as the message indicates. This is because Java is picking the most specific type that is common to the arguments it is given (both have type arguments that are Numbers that implement Comparable). To make it just use the type you're interested in, Obj<? extends Number>, call it as:

List<Obj<? extends Number>> lst = Test.<Obj<? extends Number>>lstOf(intVal, longVal);

ColinD has the detailed answer, but I would suggest instead specifying lst:

List<? extends Obj<? extends Number>> lst = lstOf(intVal, longVal);

It is a type of the parameter you're passing to the method.

If you call lstOf(String ... strs) then the result is List<String>.