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JavaIntermediate#streams
A method reference is shorthand for a lambda that calls an existing method, using :: syntax. Types include static (Class::staticMethod), instance on a particular object (obj::method), instance on an arbitrary object (Class::instanceMethod), and constructor references (Class::new).
List<String> names = List.of("bob","amy");
names.forEach(System.out::println); // instance method reference on particular object
names.stream().map(String::toUpperCase); // instance method on arbitrary object