Don't understand output from collect(), please help me :    /* please explain output from collect()  */

        import java.util.List; 
        import java.util.Arrays;
        import java.util.HashMap;
        import java.util.stream.Collectors;
    
        class example1 {
        public static void main(String []args){
            List <Integer> list = Arrays.asList(new Integer []{3,4,5,6,7,8,9});
            HashMap<Integer, List<Integer>> map = 
        list.parallelStream().collect(Collectors.groupingByConcurrent(i->i%2 == 0?1:2));   /* what's problem here */
            System.out.println(map.get(0));
                  }
             }  
/*/* output
/*java: incompatible types: inference variable R has incompatible bounds
/*    equality constraints: /*java.util.concurrent.ConcurrentMap<java.lang.Integer,java.util.List<java.lang./* Integer>>
/*    upper bounds: /*java.util.concurrent.ConcurrentHashMap<java.lang.Integer,java.util.List<java.l/*ang.Integer>>,java.lang.Object  */
  
