42. MOST COMMON MISTAKE WITH BigDecimal

• BigDecimal objects are immutable -- if you create a BigDecimal with the value of 2.00, the object will remain 2.00 and can never be changed.

• The methods such as .add(), .multiply(), and so on, return a new BigDecimal object containing the result.

• Therefore, the following two lines demonstrate right and wrong ways to do the math with BigDecimal:

  
      amountA = amountA.add( amountB ); // CORRECT -- new object is created
      amountA.add( amountB ); // INCORRECT -- attempting to update object "in place"