5

Same idea as my previous question, just a little more advanced. I want to write the following Scala code in Java:

Option(System.getProperty("not.present")).orElse(Some("default")).get

I tried this:

    final Function0<Option<String>> elseOption = new Function0<Option<String>>() { 
        @Override public Option<String> apply() { 
            return new Some<String>("default"); 
        }
    };

    final Option<String> notPresent =
        new Some<String>(System.getProperty("not.present")).
        orElse(elseOption).get();

But I get:

<anonymous OptionDemo$1> is not abstract and does not override abstract method apply$mcD$sp() in scala.Function0
[error]       orElse(new Function0<Option<String>>() {
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3
  • 4
    By the way: Option(System.getProperty("x")) getOrElse "default" is more concise and clear than what you have
    – oxbow_lakes
    Commented Jan 30, 2012 at 7:59
  • +1 on oxbow_lakes, try to always avoid doing ".get"
    – Alois Cochard
    Commented Jan 30, 2012 at 10:24
  • Good catch! I now have: Option(System.getProperty("not.present")).getOrElse("default")
    – Mike Slinn
    Commented Jan 30, 2012 at 13:16

1 Answer 1

Reset to default
2

Extend AbstractFunction0 instead of Function0. That should give you the trait-provided methods.

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  • The following always returns null in Java, although the equivalent Scala works fine. final AbstractFunction0<String> elseOption = new AbstractFunction0<String>() { @Override public String apply() { return "default"; } }; final String notPresent = (new Some<String>(System.getProperty("not.present"))).getOrElse(elseOption); Sorry, just cannot get code formatting to work in a comment.
    – Mike Slinn
    Commented Jan 30, 2012 at 13:18
  • @MikeSlinn Make another question about it. They don't charge per question here, y'know? :-)
    – Daniel C. Sobral
    Commented Jan 30, 2012 at 16:24
  • @MikeSlinn but, basically, because you used Some, it will always return the content of Some. It is Option, not Some, that turns nulls into None.
    – Daniel C. Sobral
    Commented Jan 30, 2012 at 16:25

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