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    <p>Guava team member here.</p> <p>Probably the single biggest disadvantage of <code>null</code> is that it's not obvious what it should mean in any given context: it doesn't have an illustrative name. It's not always obvious that <code>null</code> means "no value for this parameter" -- heck, as a return value, sometimes it means "error", or even "success" (!!), or simply "the correct answer is nothing". <code>Optional</code> is frequently the concept you actually mean when you make a variable nullable, but not always. When it isn't, we recommend that you write your own class, similar to <code>Optional</code> but with a different naming scheme, to make clear what you actually mean.</p> <p>But I would say the biggest advantage of <code>Optional</code> isn't in readability: the advantage is its idiot-proof-ness. It forces you to actively think about the absent case if you want your program to compile at all, since you have to actively unwrap the <code>Optional</code> and address that case. Null makes it disturbingly easy to simply forget things, and though FindBugs helps, I don't think it addresses the issue nearly as well. This is especially relevant when you're returning values that may or may not be "present." You (and others) are far more likely to forget that <code>other.method(a, b)</code> could return a <code>null</code> value than you're likely to forget that <code>a</code> could be <code>null</code> when you're implementing <code>other.method</code>. Returning <code>Optional</code> makes it impossible for callers to forget that case, since they have to unwrap the object themselves.</p> <p>For these reasons, we recommend that you use <code>Optional</code> as a return type for your methods, but not necessarily in your method arguments.</p> <p>(This is totally cribbed, by the way, from the discussion <a href="https://plus.google.com/103410944693236881656/posts/ayfR8F56PGy" rel="noreferrer">here</a>.)</p>
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    1. POWhat's the point of Guava's Optional class
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    1. USLouis Wasserman
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    1. CO+1 for a great explanation. I don't know if this is the inspiration, but I would add a pointer to option types in SML, OCaml, and F#, which have many of the same semantics.
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      1. USAdam Mihalcin
    2. COAlways great to get answer from someone who was directly involved. I'd have +1'd just for that. Would +1 more for a great answer. (but I can't.) I think the point about having it as a return value to force consumers of a unfamiliar method to make an effort to acknowledge that a "nothing" can be returned is one compelling reason. I don't like though how it is being overused (or even abused). e.g, I feel really uneasy when seeing people put Optionals as values into Maps. Map returing null for a non-existent/unmapped key is a well established paradigm... No need to make it more complicated...
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    3. COIt's well-established that `Map` returns `null` if a key is unmapped, but recall that if you do `map.put(key, null)`, then `map.containsKey(key)` will return `true` but `map.get(key)` will return `null`. `Optional` can be handy in clearing up the distinction between the "explicitly mapped to null" case and the "not present in the map" case. I'll grant that `Optional` can be abused, but I'm not yet convinced that the case you describe is an abuse.
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      1. USLouis Wasserman
 

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