Sample: LoanCalculator

LoanCalculator.java, Loan.java

  /*

   Introduction to OOP with Java (5th Ed), McGraw-Hill

 

   Wu/Otani

 

   Chapter 4 Sample Development: Loan Calculation (Step 5)

 

   File: Step5/LoanCalculator.java

 

   This class controls the input, computation, and output of loan

 */

 import java.text.DecimalFormat;

import java.util.*;

 class LoanCalculator {

// ----------------------------------

//     Data Members

// ----------------------------------

      // This object does the actual loan computation

     private Loan loan;

    

     private Scanner scanner;

// ----------------------------------

 //

//   Main Method

 //

// ----------------------------------

     public static void main(String[] arg) {

        

         LoanCalculator calculator = new LoanCalculator();

         calculator.start();

     }

// ----------------------------------

//     Constructors

// ----------------------------------

     public LoanCalculator() {

        

         scanner = new Scanner(System.in);

        

     }

// -------------------------------------------------

//       Public Methods:

 //

//           void start (        )

 //

// ------------------------------------------------

     //Top-level method that calls other private methods

     public void start() {

         describeProgram();   //tell what the program does

         getInput();          //get three input values

         displayOutput();     //display the results

     }

// -------------------------------------------------

//       Private Methods:

 //

//       void    describeProgram   (        )

//       void    displayOutput     (        )

//       void    getInputs         (        )

 //

// ------------------------------------------------

     // Provides a brief explanation of the program to the user.

     private void describeProgram() {

         System.out.println("This program computes the monthly and total");

         System.out.println("payments for a given loan amount, annual ");

         System.out.println("interest rate, and loan period (# of years).");

         System.out.println("\n");

     }

     //Displays the input values and monthly and total payments.

     private void displayOutput() {

        

         DecimalFormat df = new DecimalFormat("0.00");

        

         System.out.println("Loan Amount: $" + loan.getAmount());

         System.out.println("Annual Interest Rate:"

                             + loan.getRate() + "%");

         System.out.println("Loan Period (years): " + loan.getPeriod());

         System.out.println("Monthly payment is $ " +

                                        df.format(loan.getMonthlyPayment()));

         System.out.println("  TOTAL payment is $ " +

                                        df.format(loan.getTotalPayment()));

     }

     // Gets three input values--loan amount, interest rate, and

     // loan period

     private void getInput() {

         double  loanAmount, annualInterestRate;

         int     loanPeriod;

         System.out.print("Loan Amount (Dollars+Cents):");

         loanAmount  = scanner.nextDouble();

         System.out.print("Annual Interest Rate (e.g., 9.5):");

         annualInterestRate = scanner.nextDouble();

         System.out.print("Loan Period - # of years:");

         loanPeriod  = scanner.nextInt();

         //create a new loan with the input values

         loan = new Loan(loanAmount, annualInterestRate,loanPeriod);

     }

 }

//---------------------

// Loan Class (Step 5)

/*

   Introduction to OOP with Java (5th Ed), McGraw-Hill

 

   Wu/Otani

 

   Chapter 4 Sample Development: Loan Calculation (Step 5)

 

   File: Step5/Loan.java

 

   NO CHANGES from STEP 4 CODE

  

   This class handles the loan computation.

*/

class Loan {

//----------------------------------

//    Data Members

//----------------------------------

    // Constant for the number of months in a year

    private final int MONTHS_IN_YEAR = 12;

    // The amount of the loan

    private double    loanAmount;

    //The monthly interest rate

    private double    monthlyInterestRate;

    // The number of monthly payments

    private int       numberOfPayments;

//----------------------------------

//    Constructor

//----------------------------------

    //Creates a new Loan object with passed values.

    public Loan(double amount, double rate, int period) {

        setAmount(amount);

        setRate  (rate  );

        setPeriod(period);

    }

//-------------------------------------------------

//      Public Methods:

//

//          double  getAmount   (           )

//          double  getPeriod   (           )

//          int     getRate     (           )

//

//          double  getMontlyPayment(       )

//          double  getTotalPayment (       )

//

//          void    setAmount   ( double    )

//          void    setPeriod   ( int       )

//          void    setRate     ( double    )

//

//------------------------------------------------

    //Returns the loan amount.

    public double getAmount( ) {

        return loanAmount;

    }

    //Returns the loan period in the number of years.

    public int getPeriod( ) {

        return numberOfPayments / MONTHS_IN_YEAR;

    }

    //Returns the annual interest rate.

    public double getRate( ) {

        return monthlyInterestRate * 100.0 * MONTHS_IN_YEAR;

    }

   

    //Returns the monthly payment

    public double getMonthlyPayment( ) {

        double monthlyPayment;

        monthlyPayment = (loanAmount * monthlyInterestRate)

                           /

                         (1 - Math.pow(1/(1 + monthlyInterestRate),

                                          numberOfPayments ) );

        return monthlyPayment;

    }

   

    //Returns the total payment

    public double getTotalPayment( ) {

        double totalPayment;

        totalPayment = getMonthlyPayment( ) * numberOfPayments;

        return totalPayment;

    }

    //Sets the loan amount of this loan.

    public void setAmount(double amount) {

        loanAmount = amount;

    }

    //Sets the interest rate of this loan.

    public void setRate(double annualRate) {

        monthlyInterestRate = annualRate / 100.0 / MONTHS_IN_YEAR;

    }

    //Sets the loan period of this loan.

    public void setPeriod(int periodInYears) {

        numberOfPayments = periodInYears * MONTHS_IN_YEAR;

    }

}