Static methods in Interfaces with Java 8

Java 8 is here! That was a long wait. I mean for people who like to wait for the thing to be fully released before they even try it. I know a lot of people who even think they need to wait until Java 9 is out to start to use Java 8. For me the wait for a little shorter since I’ve been using Java 8 for quite some time and even shipped apps with it. Small apps but real apps.

Anyway, let’s take a look at one of the new features that I really like. People talked a lot about default methods in interfaces. They are great! Another great thing is static methods in interfaces. I really love those.

You remember those times where you had a Function interface and a Functions class with a bunch of static methods to create specific implementations of Function? Take a look at Guava code. It uses a lot this pattern. And we used to like it.

Now time has come to merge these two classes. We can put all static methods of Functions back into Function like this:

public interface Function<T, R> {
  R apply(T t);

  static Function<?, String> toStringFunction() {
    return value -> value.toString();
  }

  static <E> Function<E, E> identity() {
    return value -> value;
  }

  static <R> Function<?, R> constant(R constantValue) {
    return value -> constantValue;
  }
}