Complete Program

Here is the complete program. Notice how the pieces fit together. The counting loop is nested in the body of the result-controlled loop.

public class  MillionDollarInterestRate
{

  public static void main( String[] args ) 
  {
    double initialAmount = 1000.00 ;
    double dollars = 0.0;
    double rate = -0.001 ;
 
    while ( dollars < 1000000 )
    {
       // change to the next rate
       rate = rate + 0.001;

       // compute the dollars after 40 years at the current rate
       int year =  1 ;     
       dollars = initialAmount;     
       while (  year <= 40 )
       {     
         dollars = dollars + dollars*rate  ; // add another year's interest     
         dollars = dollars + 1000 ;          // add in this year's contribution
         year    =  year + 1 ;
       }

    }

    System.out.println("After 40 years at " + rate*100 
      + " percent interest you will have " + dollars + " dollars" );
  }

}

Here is a run of the program:

C:\JavaSource\>javac MillionDollarInterestRate.java

C:\JavaSource\>java MillionDollarInterestRate
After 40 years at 12.600000000000009 percent interest you will have 1021746.3104116677 dollars

The program has some floating point accuracy problems. In practice, financial programs are very carefully written and use floating point with extreme caution. Programming languages intended for business have special data formats for money that ensure that none of it gets lost.

dollars = initialAmount;