Passing Java class as argument to JRuby method

Question

I want to pass a Java class to a JRuby method, and instantiate the class object in the method (I want a generic way of running some tests on a set of Java classes, and also need to instantiate a number of these objects, not known until runtime):

#...
somethingMethod(Bar)
#....

def somethingMethod(javaClass)
  number.each do |n|
    fu=javaClass.new
   #...otherStuff
  end
end

But this does not seem to be doable in this fashion. I get:

Failure/Error: somethingMethod(Bar)
     NameError:
       uninitialized constant Bar
     # somethingTest.rb:45:in `(root)'

I've also tried to use the fully qualified class name: same results. Thanks.

Answer 1

For this, use java_class attribute of the JRuby wrapped class.

In your code

javaClass.java_class.new

should work.

You should also use this attribute, when Java method expects Java class as a parameter.

For more examples, see https://github.com/jruby/jruby/wiki/CallingJavaFromJRuby

Answer 2

This works fine for me--are you importing the class? Requiring "java"?

jruby-1.6.2 :001 > def foo(c)
jruby-1.6.2 :002?>   cc = c.new
jruby-1.6.2 :003?>   puts ">>#{cc}<<"
jruby-1.6.2 :004?>   end
jruby-1.6.2 :005 > foo(String)
>><<
jruby-1.6.2 :007 > foo(ArrayList)
NameError: uninitialized constant ArrayList
jruby-1.6.2 :008 > foo(java.util.ArrayList)
jruby-1.6.2 :009 > require 'java'
jruby-1.6.2 :010 > foo(java.util.ArrayList)
>>[]<<