Functional Programming in Java

Joining Elements

We’ve explored how to select elements, iterate, and transform collections. Yet in a trivial operation—concatenating a collection—we could lose all the gains we made with concise and elegant code if not for a newly added join function. This simple method is so useful that it’s poised to become one of the most used functions in the JDK. Let’s see how to use it to print the values in a list, comma separated.

Let’s work with our friends list. What does it take to print the list of names, separated by commas, using only the old JDK libraries?

We have to iterate through the list and print each element. Since the Java 5 for construct is better than the archaic for loop, let’s start with that.