Java 8 Lambdas

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 abstraction. 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 method. You can use method references in the same places as lambda expressions.

You can also call constructors using the same abbreviated syntax. If you ...