reference to an instance method of an arbitrary object of a particular type
The lambda equivalent of
String::compareToIgnoreCase
would be
(String a, String b) -> a.compareToIgnoreCase(b)
// 2
String::toLowerCase;
(String someString) -> someString.toLowerCase();
//3
Function<Long, Double> converter = Long::doubleValue;
Function<Long, Double> converter = val -> val.doubleValue();