/**
     * This function returns the check_modified method from the class type provided.
     *
     * @param theClass the class in which to find the check_modified method
     * @return the check_modified method if it exists
     * @throws RuntimeException if check_modified does not exist.
     */
    private static Method getCheckModified(Class<? extends Invariant> theClass) {
      Method[] methods = theClass.getMethods();

      Method currentMethod;
      for (int i = 0; i < methods.length; i++) {
        currentMethod = methods[i];
        if (currentMethod.getName().lastIndexOf("check_modified")
            != -1) { // Method should be called check_modified
          return currentMethod;
        }
      }
      throw new RuntimeException("Cannot find check_modified method");
    }
    /**
     * @return the method of invariant named by theClass that produces a String representation of
     *     the invariant.
     */
    private static Method getOutputProducer(Class<? extends Invariant> theClass) {
      Method[] methods = theClass.getMethods();

      Method currentMethod;
      for (int i = 0; i < methods.length; i++) {
        currentMethod = methods[i];

        // Method should be called format_using
        if (currentMethod.getName().lastIndexOf("format_using") != -1) {
          return currentMethod;
        }
      }
      throw new RuntimeException("Cannot find format_using method");
    }