javacastingjrubyjruby-java-interop

Casting objects in JRuby

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.

Solution

  • 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