Advanced Collections and Collectors - Java 8 Lambdas - page 63

Chapter 5. Advanced Collections and
Collectors
There's a lot more to the collections library changes than I covered in Chapter 3 . It's time to
cover some of the more advanced collections changes, including the new Collector abstrac-
tion. I'll also introduce method references, which are a way of using existing code in lambda
expressions with little to no ceremony. They pay huge dividends when it comes to writing
Collection -heavy code. More advanced topics within the collections library will also be
covered, such as element ordering within streams and other useful API changes.
Method References
A common idiom you may have noticed is the creation of a lambda expression that calls a
method on its parameter. If we want a lambda expression that gets the name of an artist, we
would write the following:
artist -> artist . getName ()
This is such a common idiom that there's actually an abbreviated syntax for this that lets you
reuse an existing method, called a method reference . If we were to write the previous lambda
expression using a method reference, it would look like this:
Artist: : getName
The standard form is Classname::methodName . Remember that even though it's a method,
you don't need to use brackets because you're not actually calling the method. You're
providing the equivalent of a lambda expression that can be called in order to call the meth-
od. You can use method references in the same places as lambda expressions.
You can also call constructors using the same abbreviated syntax. If you were to use a
lambda expression to create an Artist , you might write: