How would you display the output as +00321.00?

The correct choice for displaying the output as +00321.00 is derived from understanding how printf formatting works in Java.

In this case, using System.out.printf("+%09.2f", 321.0) achieves the desired format because of specific formatting flags:

1. The + sign specifies that the output should include a positive sign for positive numbers.
2. The 09 indicates that the total width of the output should be at least 9 characters wide, including the sign, digits, and decimal point. If the number doesn't fill this width, it will be padded with zeros on the left.
3. The .2f part means to format the number as a floating point with two digits after the decimal.

When combined, these parts format the number 321.0 as +00321.00. The output will include three leading zeros to fill up to a total width of 9 characters, along with the positive sign and the two decimal places.

This option correctly satisfies all the requirements for producing the desired result.