Optionals #

Java provides an Optional API for handling missing values with functional combinators.

Optional is primarily intended for use as a method return type where there is a clear need to represent “no result,” and where using null is likely to cause errors.

The combinators map, filter and flatMap are useful for handling optional values, but their use does not come naturally to programmers who are used to conventional programming patterns involving null checks. After introducing the Optional interface via unit tests demonstrating the behaviour of the mentioned combinators, we show how to transform traditional null checks into idiomatic use of optionals. We will also discuss anti-patterns when programming with optionals and how to avoid them.

Our discussion provides another example of how the functional combinators can be used as powerful combining forms for building new programs from existing ones while employing useful properties for reasoning about programs as mentioned in the introduction to this tutorial. More specifically, we will see how programs that would conventionally use sequencing and conditional statements can be expressed using expressions involving functional interfaces with optionals. Presenting this combinatorial style of programming by means of the relatively simple type of optionals will serve as a bridge to combinatorial parsing and can help consolidate and expand intuitions assiciated with map, filter and flatMap that are independent of concrete types implementing these combinators.