Replace your if..else if…/ nested if-not-null -then-get blocks with Java 8 Optional(s)

Optional is a welcome inclusion in Java 8, famously as an alternative for null values. The main intent of Optional was supplying non-null return values for library methods when the actual result was like no-result.

Described here is a step ahead, over this, on how to replace a specific if..else chaining with an elegant looking block using Optionals.

Full-fledged samples for the examples mentioned below are implemented both in Java 8 and pre-Java 8 —

https://github.com/abksrv/optional-chaining-comparison-if-else.git

if..else if…

In general, the following types of if..else block:

if(check1(obj) != null) 
  doSomething(check1(obj))
else if(check2(obj) != null)    
  doSomething(check2(obj))    
  /*...*/    
else if(checkN(obj) != null)    
  doSomething(checkN(obj))
/*where check1..checkN are homogeneous checks on obj (with same return type).*/

can be prettified on Java 8 as:

check1(obj).map(Optional::of)    
  .orElseGet(() -> check2(obj)).map(Optional::of)
  /*...*/    
  .orElseGet(() -> checkN(obj))    
  .ifPresent(checkResult -> doSomething(checkResult));
/*where check1..checkN are homogeneous checks on obj returning Optional of same type or empty Optional instead of null.*/

Or, more elegantly on Java 9 onward as:

check1(obj)    
  .or(() -> check2(obj))
  /*...*/    
  .or(() -> checkN(obj))    
  .ifPresent(checkResult -> doSomething(checkResult));

Not only this piece is Null Pointer Exceptions proof, it is also more readable and gets rid of ugly ‘!= null’s.

A little explanation:

The checkK methods in the Java 8 fragments return Optional objects instead of null. The intended action for the first non-empty Optional only will be done inside ifPresent at line 5.

As an example, consider the following password validation fragment using the said Optional chaining in Java 8 -

Validates an input String password in the sequence — minimumLengthValidator, numericCharactersValidator, upperCaseCharactersValidator. Returns as soon as the first first failure is encountered without looking for further validations. The returned Optional contains details on failure if validation fails, else is empty. Link to repository provided at start of this article.

Instead of .orElseGet(() -> checkK()),

check1(obj).map(Optional::of).orElse(check2(obj))...

would also yield the correct result, but this would unnecessarily call all the checkK methods although we require it to be called only until we get a first non-empty Optional.

if-not-null-then-get nested blocks

I hope the following must be very common —

If the getters in the above code are made to return Optional objects instead of null, this becomes pretty like —

Another little explanation:

flatMap maps the value present in the Optional to an Optional which describes the result of applying the specified Function to that value. If no value was present in the Optional, it returns an empty Optional.

There are few other usage of Optional including Stream features using stream method. So, start replacing your null return values and share your other Optional practices. :)

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