Casting objects in JRuby

Question

Is there a way I can explicitly cast one Java object to another Java class from JRuby?

Sometimes I want to be able to invoke SomeJavaClass#aMethod(MySuperClass) rather than SomeJavaClass#aMethod(MyClass) from JRuby.

From Java, I'd do this:

someJavaObject.aMethod( (MySuperClass) myObj );

but I didn't see a #cast ruby method or anything like that to do the equivalent from JRuby.

Note that the question Casting Java Objects From JRuby lacks an answer for the general case, which is why I'm re-asking the question.

Nikita Fedyashev · Accepted Answer · 2020-10-23 11:00:33Z

11

You need to make use of either the #java_send or #java_alias feature available starting with JRuby 1.4 to select the method you wish to call. Example:

class Java::JavaUtil::Arrays
  boolean_array_class = [false].to_java(:boolean).java_class
  java_alias :boolean_equals, :equals, [boolean_array_class, boolean_array_class]
end

a1 = [false, true]
Java::JavaUtil::Arrays.boolean_equals a1, a1
# => TypeError: for method Arrays.equals expected [class [Z, class [Z]; got: [org.jruby.RubyArray,org.jruby.RubyArray]; error: argument type mismatch
Java::JavaUtil::Arrays.boolean_equals a1.to_java(:boolean), a1.to_java(:boolean)
# => true
a2 = [true, false]
Java::JavaUtil::Arrays.boolean_equals a1.to_java(:boolean), a2.to_java(:boolean)
# => false

edited Oct 23, 2020 at 11:00

Nikita Fedyashev

19.3k15 gold badges58 silver badges110 bronze badges

answered Nov 24, 2009 at 22:02

Nick Sieger

3,31523 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

gregoltsov Over a year ago

I think it would be useful to add that if you're trying to cast to non-primitive classes, you should use the full hierarchy. So, say, to to cast obj to ij.text.TextWindow class, you'd have to write obj.to_java(Java::Ij::text::TextWindow).

Collectives™ on Stack Overflow

Casting objects in JRuby

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related