I do not have idea what am doing wrong. in the below stream api related code snippet

Question

Following is the code that gives me error "Bad return type in lambda expression: U cannot be converted to Integer". I do not understand why it needs Integer here as the keys are String.

public static void main(String[] args) {

        String input="java is headache";
        //-1st non repeated char using stream
        String [] arr= input.split("");
        List<String> myList= Arrays.asList(arr);
        System.out.println(myList);

        Map<String ,Long > myMap=myList.stream()
                .collect(toMap(Function.identity(), String::length,
                *(e1, e2) -> e2*, LinkedHashMap::new));




    }

Highlighted area is the piece of code showing as incorrect in the IDE.

Answer 1

You have incorrectly declared the type of myMap, which throws off the compiler:

        Map<String, Integer> myMap = myList.stream()
                .collect(Collectors.toMap(Function.identity(), String::length,
                        (e1, e2) -> e2, LinkedHashMap::new));

In general, the compiler often gives generics-related errors in the wrong place. It can help to separate out all parts, and explicitly typing them. In this case, I extracted the third parameter to a BinaryOperator<Integer> variable, which pointed me to the real error.