Stream mapToLong(ToLongFunction mapper) returns a LongStream consisting of the results of applying the given function to the elements of this stream.
Stream mapToLong(ToLongFunction mapper) is an intermediate operation. These operations are always lazy. Intermediate operations are invoked on a Stream instance and after they finish their processing, they give a Stream instance as output.
LongStream mapToLong(ToLongFunction<? super T> mapper) Where, LongStream is a sequence of primitive long-valued elements and T is the type of stream elements. mapper is a stateless function which is applied to each element and the function returns the new stream.
Example 1 : mapToLong() function with operation of returning stream satisfying the given function.
The stream after applying the function is : 225
Example 2 : mapToLong() function with returning number of set-bits in string length.
4 1 1 3 2