A converter converts a source object of type S to a target of type T . Use Java 8’s core Functional Interfaces. Functional Interfaces How does lambda expressions fit into Javas type system? Static Method : Integer.valueOf(String number) -> Integer::valueOf(this is method references) 2. In contrast, when you are using the Java Collections iteration features (e.g a Java Iterator or the Java for-each loop used with a Java Iterable) you have to implement the iteration of the elements yourself.