Rama is a testament to the power of Clojure(blog.redplanetlabs.com)

  package com.rpl.specter;

  public class MutableCell {
    private Object o;

    public MutableCell(Object o) {
      this.o = o;
    }

    public Object get() {
      return o;
    }

    public void set(Object o) {
      this.o = o;
    }
  }