IKataSolution.java

package org.codingkata.unit.api;

public interface IKataSolution {
   String reply();
}

my_kata.rb

java_import 'org.codingkata.unit.api.IKataSolution'

class MyKata
 java_implements IKataSolution

 java_signature 'String reply()'
 def reply
   # your reply code here
 end
end

MyKata.java

import org.jruby.Ruby;
import org.jruby.RubyObject;
import org.jruby.javasupport.util.RuntimeHelpers;
import org.jruby.runtime.builtin.IRubyObject;
import org.jruby.javasupport.JavaUtil;
import org.jruby.RubyClass;
import org.codingkata.unit.api.IKataSolution;


public class MyKata extends RubyObject implements IKataSolution {
    private static final Ruby __ruby__ = Ruby.getGlobalRuntime();
    private static final RubyClass __metaclass__;

    static {
        String source = new StringBuilder("java_import org.codingkata.unit.api.IKataSolution\n" +
            "\n" +
            "class MyKata\n" +
            " java_implements IKataSolution\n" +
            "\n" +
            " java_signature \"String reply()\"\n" +
            " def reply\n" +
            "   # your reply code here\n" +
            " end\n" +
            "end\n" +
            "").toString();
        __ruby__.executeScript(source, "my_kata.rb");
        RubyClass metaclass = __ruby__.getClass("MyKata");
        metaclass.setRubyStaticAllocator(MyKata.class);
        if (metaclass == null) throw new NoClassDefFoundError("Could not load Ruby class: MyKata");
        __metaclass__ = metaclass;
    }

    /**
     * Standard Ruby object constructor, for construction-from-Ruby purposes.
     * Generally not for user consumption.
     *
     * @param ruby The JRuby instance this object will belong to
     * @param metaclass The RubyClass representing the Ruby class of this object
     */
    private MyKata(Ruby ruby, RubyClass metaclass) {
        super(ruby, metaclass);
    }

    /**
     * A static method used by JRuby for allocating instances of this object
     * from Ruby. Generally not for user comsumption.
     *
     * @param ruby The JRuby instance this object will belong to
     * @param metaclass The RubyClass representing the Ruby class of this object
     */
    public static IRubyObject __allocate__(Ruby ruby, RubyClass metaClass) {
        return new MyKata(ruby, metaClass);
    }
        
    /**
     * Default constructor. Invokes this(Ruby, RubyClass) with the classloader-static
     * Ruby and RubyClass instances assocated with this class, and then invokes the
     * no-argument 'initialize' method in Ruby.
     *
     * @param ruby The JRuby instance this object will belong to
     * @param metaclass The RubyClass representing the Ruby class of this object
     */
    public MyKata() {
        this(__ruby__, __metaclass__);
        RuntimeHelpers.invoke(__ruby__.getCurrentContext(), this, "initialize");
    }

    
    public String reply() {

        IRubyObject ruby_result = RuntimeHelpers.invoke(__ruby__.getCurrentContext(), this, "reply");
        return (String)ruby_result.toJava(String.class);

    }

}