Question

\((\)Savings Account Class) Create class SavingsAccount. Use a static variable annual Inter- estRate to store the annual interest rate for all account holders. Each object of the class contains a private instance variable savingsBal ance indicating the amount the saver currently has on deposit. Provide method calculateMonth1yInterest to calculate the monthly interest by multiplying the savingsBalance by annual InterestRate divided by 12 - this interest should be added to savingsBalance. Provide a static method modifyInterestRate that sets the annual InterestRate 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. Sct annual InterestRate to \(4 \%,\) then calculate the monthly interest and print the new balances for both savers. Then set the annual InterestRate to \(5 \%\), calculate the next month's interest and print the new balances for both savers.

Short answer

Define `SavingsAccount`, set rates, calculate interests. Update balances and print.

Step-by-step solution

Define the Class Structure

Start by creating the class `SavingsAccount`. Define a static variable `annualInterestRate` to hold the annual interest rate shared by all accounts. Add a private instance variable `savingsBalance` to represent the current balance of each account holder.

Implement the Constructor

Create a constructor for the `SavingsAccount` class that takes an initial balance as a parameter and assigns it to `savingsBalance`. This will be used to instantiate each account with a specified starting balance.

Method to Calculate Monthly Interest

Implement the `calculateMonthlyInterest` method. This method calculates interest by multiplying `savingsBalance` by `annualInterestRate / 12`. Add this interest to `savingsBalance` to update it with the new amount.

Static Method to Modify Interest Rate

Write a static method called `modifyInterestRate` that takes a new interest rate as a parameter. This method should update the static variable `annualInterestRate` with the new interest rate.

Instantiate SavingsAccount Objects

In the main program, create two instances of `SavingsAccount`. Name them `saver1` and `saver2`, initializing them with balances of $2000.00 and $3000.00, respectively.

Set Initial Annual Interest Rate and Compute Interest

Set the static `annualInterestRate` to 4% (0.04). Call the `calculateMonthlyInterest` method on both `saver1` and `saver2`. Print their new balances after adding the monthly interest.

Modify Interest Rate and Recalculate

Use the `modifyInterestRate` method to change the interest rate to 5% (0.05). Again, call `calculateMonthlyInterest` on both `saver1` and `saver2`. Print their updated balances after applying the new monthly interest rate.

Key concepts

Static Variables

Static variables are a pivotal concept in object-oriented programming. A static variable is shared among all instances of a class. This means that, regardless of how many objects are created from a class, a static variable retains its value across all of them.
In the context of the `SavingsAccount` class, the static variable `annualInterestRate` is used to store the annual interest rate that is applicable to every account. This reflects a real-world scenario where a bank might have a standard interest rate for all its savings accounts. By using a static variable, any change in the interest rate will automatically be reflected for all account instances.

• Static variables are declared with the `static` keyword.
• The value is shared among all instances of the class.
• They can be accessed without creating an instance of the class.

This makes static variables ideal for settings that need uniformity, like an interest rate in a bank class.

Class Methods

Class methods, particularly static methods, do not operate on a specific instance of a class. Instead, they belong to the class itself. These methods can be called without creating an instance of the class, and they often interact with static variables within the class.
In the `SavingsAccount` class, the method `modifyInterestRate` is a static method. It allows external code to set a new value for the `annualInterestRate` static variable. This demonstrates a key feature of class methods — they modify or provide information relevant to the class as a whole, rather than any individual object.

• Static methods are defined using the `static` keyword.
• They can't access instance variables directly since they are not tied to a specific object.
• Static methods are best used for operations that involve static variables or global changes.

This makes static methods particularly useful for operations like adjusting the shared interest rate across all account objects.

Interest Calculation

Interest calculation is an essential part of financial applications, like computing the growth of savings over time. In programming exercises, especially those involving bank accounts, understanding how to calculate and apply interest is critical.
For the `SavingsAccount` class, the monthly interest calculation is performed in the `calculateMonthlyInterest` method. This involves multiplying the `savingsBalance` by the `annualInterestRate` and dividing the result by 12 (to account for monthly interest). The calculated interest is then added to `savingsBalance`, effectively updating the balance with the accrued interest.
\[ \text{Monthly Interest} = \frac{\text{savingsBalance} \times \text{annualInterestRate}}{12} \]
This formula highlights the importance of using accurate values for `annualInterestRate` and ensuring that the rate is suitably divided to reflect monthly accrual.

Programming Exercises

Programming exercises, like creating a class for managing savings accounts, offer a practical approach to understanding object-oriented programming concepts. These exercises often involve constructing a class, implementing both static and instance methods, and manipulating variables, enabling students to actively engage with theoretical knowledge through hands-on application.
For instance, by working through the `SavingsAccount` exercise, students can learn:

• How to define and use a class to model real-world entities.
• Difference and interaction between static and instance variables and methods.
• The process of instantiating objects and modifying them through method calls.

These programming tasks help cement understanding by requiring the application of learned concepts in a structured exercise. Ultimately, solving such exercises enhances both problem-solving skills and comprehension of object-oriented principles.