gistfile1.java

 private DoubleBinding averageBinding = new DoubleBinding() {
        {
            //call #computeValue every time #values() changes
            super.bind(values());
        }
        @Override
        protected double computeValue() {
            double result = 0;
            if (values().isEmpty()) {
                return result;
            }
            for (Double d : values()) {
                result += d;
            }
            return result / values().size();
        }
    };