Savings Account Class in java

(Savings Account Class) Create class SavingsAccount. Use a static variable annualInterestRate to store the annual interest rate for all account holders. Each object of the class contains a private instance variable savingsBalance indicating the amount the saver currently has on deposit.Provide method calculateMonthlyInterest to calculate the monthly interest by multiplying the savingsBalance by annualInterestRate divided by 12 — this interest should be added to savingsBalance. Provide a static method modifyInterestRate that sets the annualInterestRate to a new value. Write a program to test class SavingsAccount. Instantiate two savingsAccount objects,saver1 and saver2, with balances of $2000.00 and $3000.00, respectively. Set annualInterestRate to 4%, then calculate the monthly interest for each of 12 months and print the new balances for both savers. Next, set the annualInterestRate to 5%, calculate the next month’s interest and print the new balances for both savers.

Savings Account Class in java Program

/*
 *       Filename:  SavingsAccount.java
 *
 *    Description:  Exercise 8.6 - Savings Account Class
 *
*  @Author:  Bilal Tahir Khan Meo
 *  Website: https://codeblah.com
 *
 * =====================================================================================
 */
public class SavingsAccount{
    private static double annualInterestRate = 0.0f;
    private double savingsBalance = 0.0f;

    // constructor
    public SavingsAccount(double savingsBalance){
        setSavingsBalance(savingsBalance);
    }
    // SETTERS
    public void setSavingsBalance(double savingsBalance){
        this.savingsBalance = savingsBalance;
    }
    // update the interest rate
    public static void modifyInterestRate(double newInterestRate){
        // check for negative interest rates
        if(newInterestRate >= 0.0f)
            annualInterestRate = newInterestRate;
        else
            throw new IllegalArgumentException("interest rate must be >= 0.0f");
    }
    // GETTERS
    public double getSavingsBalance(){
        return this.savingsBalance;
    }
    public static double getAnnualInterestRate(){
        return annualInterestRate;
    }
    // calculates the monthly interest and update the savings balance
    public void calculateMonthlyInterest(){
        savingsBalance += (savingsBalance * annualInterestRate) / 12;
    }
    // return savingsBalance as string
    public String toString(){
        return String.format("%.2f", getSavingsBalance());
    }
}

Method 2 : Savings Account Class in java Program

package savingsaccount;

public class SavingsAccount {

   //variable to store annual interest rate
        static private double annualInterestRate;
        private double savingBalance;

        //constructor method
        public SavingsAccount()
        {

        }

        //Constructor method
        public SavingsAccount(double savingBalance)
        {
                this.savingBalance=savingBalance;
        }

        //Get saving balance
        public double getSavingBalance()
        {
                return this.savingBalance;
        }
        
         // Modify interest rate by setting annual interest rate to a new value
        public static void modifyInterestRate(double newInterestRate)
        {
                annualInterestRate=newInterestRate;
        }

        //Method to calculate monthly interest 
        public void calculateMonthlyInterest()
        {
                double monthlyI; 
                monthlyI= (double)(this.savingBalance*annualInterestRate/12);
                this.savingBalance+=monthlyI;
        }


    public static void main(String[] args) {
    
                        // To test the class designed above
                //Instantiate 2 saving account objects saver1 and saver2
                SavingsAccount saver1, saver2;
                saver1 = new SavingsAccount (2000.0);
                saver2= new SavingsAccount (3000.0);
                
                int total = 0;

                //Set the annual interest rate to 4%=0.04
                SavingsAccount.modifyInterestRate (0.04);

                //Calculate monthly interest 
                saver1.calculateMonthlyInterest();
                saver2.calculateMonthlyInterest();

                //Print out the new balances for both savers
                System.out.println("This month:\nSaver 1 balance= "+ saver1.getSavingBalance());
                System.out.println("Saver 2 balance= "+ saver2.getSavingBalance());


                //Change annual interest rate to 5%=0.05
                SavingsAccount.modifyInterestRate(0.05);

                //Calculate the next month interest rate and print out balances
                saver1.calculateMonthlyInterest();
                saver2.calculateMonthlyInterest();
                System.out.println("Next month:\nSaver 1 balance= "+ saver1.getSavingBalance());
                System.out.println("Saver 2 balance= "+ saver2.getSavingBalance());

    }

Method 3 : Savings Account Class in java Program

public class SavingsAccount
{
    private static double annualInterestRate;
    private double savingsBalance;

    protected SavingsAccount()
    {
        savingsBalance = 0;
        annualInterestRate = 0;
    }

    protected SavingsAccount(double balance)
    {
        savingsBalance = balance;
        annualInterestRate = 0;
    }

    protected void calculateMonthlyInterest()
    {
        System.out.println("Current savings balance: " + savingsBalance);
        double monthlyInterest;
        monthlyInterest = (savingsBalance * annualInterestRate)/12;
        savingsBalance += monthlyInterest;
        System.out.println("New savings balance: " + savingsBalance);
    }

    protected double getBalance()
    {
        return savingsBalance;
    }

    protected static void modifyInterestRate(double newInterestRate)
    {
        annualInterestRate = newInterestRate;
    }    
}

class SpecialSavings extends SavingsAccount
{
    protected static void modifyInterestRate()
    {
        if(SavingsAccount.getBalance() > 10000)
        {
            modifyInterestRate(.1);
        }
    }
}

class Driver
{
    public static void main(String[] args)
    {
        SavingsAccount saver1 = new SavingsAccount(2000);
        SavingsAccount saver2 = new SavingsAccount(3000);

        saver1.modifyInterestRate(.04);
        saver1.calculateMonthlyInterest();
        saver2.modifyInterestRate(.04);
        saver2.calculateMonthlyInterest();

        saver1.modifyInterestRate(.05);
        saver1.calculateMonthlyInterest();
        saver2.modifyInterestRate(.05);
        saver2.calculateMonthlyInterest();
    }
}

Originally published at codeblah.com on February 15, 2019.