Java 8 Optional: combine two possibly null object

Question

I have to ensure if two values are non null. When the first and second have non null values, pass first as argument to second. If one of them are null value, then return false. This can be done in the following piece of code:

String value1 = function_to_get_value1()
if (value1 == null) return false;
String value2 = function_to_get_value2(value1)
if (value2 == null) return false;
return true;

It can also be done in short form:

try {
  return function_to_get_value2(function_to_get_value1()) != null;
} catch (NullPointerException e) {
  return false;
}

I was wondering how to do this in fluent form with Optional.

Note: `function_to_get_value2(function_to_get_value1())` doesn't match "When the first and second have non null values, pass first as argument to second." - you're always passing value1. You're also not checking value2 for being null, i.e. you'd need to do `return function_to_get_value2(function_to_get_value1()) != null` instead. — Thomas, Apr 28 '21 at 14:56
Does this answer your question? [What's the most elegant way to combine optionals?](https://stackoverflow.com/questions/32776705/whats-the-most-elegant-way-to-combine-optionals) — Zeuzif, Apr 28 '21 at 14:57

score 2 · Accepted Answer · edited May 12 '21 at 06:37

You could try something like this:

return Optional.ofNullable(function_to_get_value1())
               .map(v1 -> function_to_get_value2(v1))
               .isPresent();

map() applies the lambda if value is present and returns a new Optional.ofNullable() or otherwise returns an empty Optional. So in the end you have an empty Optional if either value was null or a non-empty one.

If you have a look at the source code for those methods, it basically is equivalent to this:

//Optional.ofNullable(...)
Optional<UiObject> v1Opt = value1 == null ? Optional.empty() : Optional.of(value1);

//Optional.map(...)
Optional<UiObject> v2Opt;
if(v1Opt.isPresent()) {
   //this is the lambda
   UiObject value2 = function_to_get_value2(value1);

   //Optional.ofNullable(...) called in map(...)
   v2Opt = value2 == null ? Optional.empty() : Optional.of(value2);
} else {
   v2Opt = Optional.empty();
}

//Optional.isPresent()
return v2Opt.value != null;

Java 8 Optional: combine two possibly null object

1 Answers1