I want to convert array into Map using Java 8 streams:
String[] arr = {"two", "times", "two", "is", "four"};
Arrays.stream(arr).collect(Collectors.toMap(s -> s, 1, Integer::sum);
The s -> s part is marked as error
no instance(s) of type variable(s) T, U exists so that Integer conforms to Function
Actually the 1 is the error. The value 1 cannot serve as the valueMapper, whose type should be Function<? super T, ? extends U>.
In your example the value mapper should be a function that accepts an element of your Stream (a String) and returns an Integer. The lambda expression s -> 1 will do.
The following works:
String[] arr = {"two", "times", "two", "is", "four"};
Map<String,Integer> map = Arrays.stream(arr).collect(Collectors.toMap(s -> s, s -> 1, Integer::sum));
System.out.println (map);
Output:
{times=1, four=1, is=1, two=2}
