Java™ How To Program (Early Objects), Tenth Edition

A Warning about Displaying Rounded Values

We declared variables amount, principal and rate to be of type double in this example. We’re dealing with fractional parts of dollars and thus need a type that allows decimal points in its values. Unfortunately, floating-point numbers can cause trouble. Here’s a simple explanation of what can go wrong when using double (or float) to represent dollar amounts (assuming that dollar amounts are displayed with two digits to the right of the decimal point): Two double dollar amounts stored in the machine could be 14.234 (which would normally be rounded to 14.23 for display purposes) and 18.673 (which would normally be rounded to 18.67 for display purposes). When these amounts are added, they produce the internal ...