Functional Interfaces vs. Function Types in Java with Lambdas

In several steps the Java type system is extended by features, which we know from functional programming languages. In Java 5.0 [GJSB05] generic types as well as a limited form of existential types (bounded wildcards) are introduced. In Java 8 the language will be expanded by lambda expressions, functional interfaces as target types, method and constructor references and default methods. In an earlier approach real function types were introduced as types of lambdas. The function types have been replaced by functional interfaces (interfaces with one method).