title: Java add method to class
body: <p>Good morning, I have a custom class cBigDecimal that extends the class BigDecimal. My goal is to use both the methods from the BigDecimal and cBigDecimal class (for example "add" or "multiply", as well as the custom function "percentage"). The problem is that "add" &amp; co. return BigDecimal, and obviously I can't cast it to cBigDecimal... Any ideas? 
  Thanks in advance,
  Lorenzo</p>