title: adding method for existing with CodeModel
body: <p>I am trying to add abstract methods to my interfaces with CodeModel. Is this possible?</p>
  
  <pre><code>JCodeModel cm = new JCodeModel();
  JClass ref = cm.ref(Sample.class);
  </code></pre>
  
  <p>After having a reference to actual class, I do not know to how I should add a method? Actually I want to use as a JDefinedClass.</p>