Big Java example project "invest"

You can use this project as follows:

 - invoke the main method of the driver class InvestmentTest by right-clicking 
 on the class representation and selecting the main method.
 - interactively create Investment objects of differing balances and rates of interest
 - call the waitForBalance method of each object specifying the target balance for the account
 - then call the getYears method to find out the projected time to reach target balance
 - use BlueJ's inspection capabilities to watch change of internal state after each call
  
This project illustrates concepts covered in Big Java, Chapter 6 
"Iteration".
  
 - to be able to program loops with the while, for, and do statements
 - to avoid infinite loops and off-by-one errors
 