java.util.function package was introduced in Java 8. It contains functional interfaces, which is described the following way in the API specification:
Functional interfaces provide target types for lambda expressions and method references. Each functional interface has a single abstract method, called the functional method for that functional interface, to which the lambda expression's parameter and return types are matched or adapted.
In this blog post I'm quickly going through 4 out of the over 40 interfaces in this package.
Read the full blog post here:
FUNCTIONAL INTERFACES IN JAVA 8