CODEWITHSUNDEEP
javaguava
Vincent Mimoun-Prat
Vincent Mimoun-Prat

Reputation: 28541

Addind an Optional.absent() element to a collection in Guava

I can't find the trick here: I want a function to return a list of optional objects in order to mean that my list does contain this many elements but that some of them are not valid. 

public Optional<String> getMyObjects() {
  List<Optional<String>> result = Lists.newArrayListWithCapacity(2);

  result.add(Optional.of("This value is valid"));
  result.add(Optional.absent()); // Compiler error

  return result;
}

This does not compile:

The method add(Optional<String>) in the type List<Optional<String>> is not 
applicable for the arguments (Optional<Object>)

How would you put it? I have tried casting without success

Upvotes: 3

Views: 1167

Answers (3)

JB Nizet
JB Nizet

Reputation: 691785

Use

result.add(Optional.<String>absent())

to force the generic type.

Or, to let the compiler infer it:

Optional<String> o = Optional.absent();
result.add(o);

Upvotes: 4

Jean Logeart
Jean Logeart

Reputation: 53829

Try:

result.add(Optional.<String> absent());

The absent() method is parametrized.

Upvotes: 3

Grzegorz Rożniecki
Grzegorz Rożniecki

Reputation: 28005

Try:

result.add(Optional.<String>absent());

Read more about parametrized methods and explicit type argument specification in great yet unofficial Java Generics FAQ.

Upvotes: 8

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