Iterative and Recursive algorithms

Question

I am fairly new to Java and am currently looking into Data structures, algorithms etc...
I have designed a very basic ADT (Abstract Data Type) class called Loan which contains the following private instance variables 'loanNo, copyNo, membershipNo, dateDueBack, totalFines'.
Basically I am trying to devise an iterative and also a recursive algorithm for calculating fines for loans not returned over a given duration. For instance if I was to assume a fixed rate of say 1% for every day the book is overdue how would I go about writing the 2 algorithms.
Both the algorithm and elements of the java code would be appreciated or any useful articles or websites that can help me to further my limited understanding of this topic.
All help is greatly appreciated.

Answer 1

I am very far from being an expert here, but:
Two important things come to mind;
1. Try to keep your calculations in one file/class it is tempting to have something like the following:
class BookTypeA
  float calculateFine()
     loanRate = 2%;
     // stuff
// and then in another file...
class BookTypeB
  float calculateFine()
     loanRate = 0.5%;
     // stuff
}Every time you update the algorithm for calculating the fines, you have to change both files, trust me, someone will notice if your calculations bend a penny one way or another.
You solve this problem by having a Visitor, there is lots of stuff on the web about the Visitor pattern. Basically:
class Calculator implements Visitor
   public int calculate( Book book  )
      //stuff here
class BookTypeA extends Book
   void calculateFine(  Visitor v )
      v.visit( this );
//main{}
for(  Book bk : myBooks  )
    bk.calculateFine( calculator );
// etc.2. Separate your calculations into discreet functions, notice the difference in the following two "calculators"...
class Calculator
   float getFine( int daysoverdue )
      if(  !senior )
          float result = daysoverdue * 0.01f;
          result += ( int tax = result * 0.08f );
          result += ( previousFines );
          result -= ( float seniorsdiscount = result * 0.10f );
       //etc, etc.
// The WAY BETTER version
class Calculator
   float getFine( int daysoverdue )
      if(  !senior )
          float baseAmount = calculateBaseFines( daysoverdue );
          float taxAmount = calculateTax( baseAmount );
          float previousFines = addPreviousFines(  );
           float subTotal = baseAmount + taxAmount + previousFines;
          float seniorsDiscount = applySeniorsDiscount(  subTotal );
       //etc, etc.
      // one calculation per function
      float calculateTax(  float baseamount )
          taxRate = 0.08;
          return baseAmount * taxRate;
      // rest of the functions
} In short be really explicit. Really clear. Chasing tax rates through program headers, global definitions, main classes is really rough. Put the tax rate right next to the calculation. Perform one calculation per function, stuff like this; int rate += ( amount * tax ) + zot; is impossible to debug.
Hope that helps some.
Andrew