Thread: Designing an Account Class

Design a class named Account that contains:

• A private int data field named id for the account(default 0)
• A private double data field named balance for the account (default 0)
• A private double data field named annualInterestRate that stores the current interest rate (default 0). Assume all accounts have the same interest rate.
• A private Date data field named dateCreated that stores the date when the account was created.
• A no-arg constructor that creates a default account.
• A constructor that creates an account with the specific id and initial balance.
• The accessor and mutator methods for id, balance, and annualInterestRate.
• The accessor method for dateCreated
• A method named getMonthlyInterestRate() that returns the monthly interest rate.
• A method named withdraw that withdraws a specified amount from the account
• A method named deposit that deposits a specified amount to the account.

Write a test program that creates an Account object with an account ID of 1122, a balance of $20,000, and an annual interest rate of 4.5%. Use the withdraw method to withdraw $2,500, use the deposit method to deposit $3,000 and print the balanace, the monthly interest, and the date when this account was created.

Here is my attempt:

import java.util.Date;
 
public class AccountProblem {
    public static void main(String[] args) {
//create an instance  object of class Stock
        Account myAccount = new Account(1122, 20000.00, 0.045);
        myAccount.withdraw(2500.00);
        myAccount.deposit(3000.00);
//display balance, monthly interest and date of account
        System.out.println("Balance: " + myAccount.balance);
        System.out.println("Monthly Interest: " + myAccount.getMonthlyInterestRate());
        System.out.println("Account created on: " + myAccount.dateCreated);
    }
}
 
class Account {
//define var1, var2
    int id;
    double balance;
    double annualInterestRate;
    Date dateCreated;
//no arg constructer
    Account() {
        id = 0;
        balance = 0.0;
        annualInterestRate = 0.0;
    }
//constructor with specific id and initial balance
    Account(int newId, double newBalance) {
        id = newId;
        balance = newBalance;
    }
//accessor/mutator methods for id, balance, and annualInterestRate
    public int getId() {
        return id;
    }
    public double getBalance() {
        return balance;
    }
    public double getAnnualInterestRate() {
        return annualInterestRate;
    }
    public void setId() {
        id = newId;
    }
    public void setBalance() {
        balance = newBalance;
    }
    public void setAnnualInterestRate() {
        annualInterestRate = newAnnualInterestRate;
    }
//accessor method for dateCreated
    public void setDateCreated() {
        dateCreated = newDateCreated;
    }
//define method getMonthlyInterestRate
    double getMonthlyInterestRate() {
        return annualInterestRate/12;
    }
//define method withdraw
    double withdraw(double amount) {
        return balance -= amount;
    }  
//define method deposit
    double deposit(double amount) {
        return balance += amount;
    }
}

My code does not compile. And I get the following error messages. I have no clue what the error messages mean and how I would fix them.

AccountProblem.java:10: cannot find symbol
symbol : constructor Account(int,double,double)
location: class Account
Account myAccount = new Account(1122, 20000.00, 0.045);
^
AccountProblem.java:48: cannot find symbol
symbol : variable newId
location: class Account
id = newId;
^
AccountProblem.java:51: cannot find symbol
symbol : variable newBalance
location: class Account
balance = newBalance;
^
AccountProblem.java:54: cannot find symbol
symbol : variable newAnnualInterestRate
location: class Account
annualInterestRate = newAnnualInterestRate;
^
AccountProblem.java:58: cannot find symbol
symbol : variable newDateCreated
location: class Account
dateCreated = newDateCreated;
^
5 errors

How can I get my program to compile and work?

"You attempt to access a constructor in the Account class with 3 parameters - there is no constructor of that definition."
I'm trying to access this constructor:

//constructor with specific id and initial balance
    Account(int newId, double newBalance) {
        id = newId;
        balance = newBalance;
    }

How would I access this constructor?

"Where is the newBalance variable?"
I don't know. Where in my code do I put it?

Yes I did. I'm guessing you are doWhile over on that forum. I fixed up my code and got it to compile.

Here is the revised code:

import java.util.Date;
 
public class AccountProblem {
	public static void main(String[] args) {
//create an instance  object of class Stock
		Account myAccount = new Account(1122, 20000.00, 0.045);
		myAccount.withdraw(2500.00);
		myAccount.deposit(3000.00);
//display balance, monthly interest and date of account
		System.out.println("Balance: " + myAccount.balance);
		System.out.println("Monthly Interest: " + myAccount.getMonthlyInterestRate());
		System.out.println("Account created on: " + myAccount.dateCreated);
	}
}
 
class Account {
//define var1, var2
	int id;
	double balance;
	double annualInterestRate;
	Date dateCreated;
//no arg constructer
	Account() {
		id = 0;
		balance = 0.0;
		annualInterestRate = 0.0;
	}
//constructor with specific id and initial balance
	Account(int newId, double newBalance) {
		id = newId;
		balance = newBalance;
	}
	Account(int newId, double newBalance, double newAnnualInterestRate) {
		id = newId;
		balance = newBalance;
		annualInterestRate = newAnnualInterestRate;
	}
//accessor/mutator methods for id, balance, and annualInterestRate
	public int getId() {
		return id;
	}
	public double getBalance() {
		return balance;
	}
	public double getAnnualInterestRate() {
		return annualInterestRate;
	}
	public void setId(int newId) {
		id = newId;
	}
	public void setBalance(double newBalance) {
		balance = newBalance;
	}
	public void setAnnualInterestRate(double newAnnualInterestRate) {
		annualInterestRate = newAnnualInterestRate;
	}
//accessor method for dateCreated
	public void setDateCreated(Date newDateCreated) {
		dateCreated = newDateCreated;
	}
//define method getMonthlyInterestRate
	double getMonthlyInterestRate() {
		return annualInterestRate/12;
	}
//define method withdraw
	double withdraw(double amount) {
		return balance -= amount;
	}	
//define method deposit
	double deposit(double amount) {
		return balance += amount;
	}
}

The only problem is my output.

Balance: 20500.0
Monthly Interest: 0.00375
Account created on: null

I don't know why null is showing up. How can I get the date to show up? And thanks.

You need to initialise the Date class object, check Date (Java 2 Platform SE v1.4.2) for guidance.

Nevermind I got it.

Here's the finished code:

import java.util.Date;
 
public class AccountProblem {
	public static void main(String[] args) {
//create an instance  object of class Stock
		Account myAccount = new Account(1122, 20000.00, 0.045);
		myAccount.withdraw(2500.00);
		myAccount.deposit(3000.00);
//display balance, monthly interest and date of account
		System.out.println("Balance: " + myAccount.balance);
		System.out.println("Monthly Interest: " + myAccount.getMonthlyInterestRate());
		//System.out.println("Account created on: " + myAccount.dateCreated);
		java.util.Date dateCreated = new java.util.Date();
		System.out.println("Account created on: " + dateCreated.toString());
	}
}
 
class Account {
//define var1, var2
	int id;
	double balance;
	double annualInterestRate;
	Date dateCreated;
//no arg constructer
	Account() {
		id = 0;
		balance = 0.0;
		annualInterestRate = 0.0;
	}
//constructor with specific id and initial balance
	Account(int newId, double newBalance) {
		id = newId;
		balance = newBalance;
	}
	Account(int newId, double newBalance, double newAnnualInterestRate) {
		id = newId;
		balance = newBalance;
		annualInterestRate = newAnnualInterestRate;
	}
//accessor/mutator methods for id, balance, and annualInterestRate
	public int getId() {
		return id;
	}
	public double getBalance() {
		return balance;
	}
	public double getAnnualInterestRate() {
		return annualInterestRate;
	}
	public void setId(int newId) {
		id = newId;
	}
	public void setBalance(double newBalance) {
		balance = newBalance;
	}
	public void setAnnualInterestRate(double newAnnualInterestRate) {
		annualInterestRate = newAnnualInterestRate;
	}
//accessor method for dateCreated
	public void setDateCreated(Date newDateCreated) {
		dateCreated = newDateCreated;
	}
//define method getMonthlyInterestRate
	double getMonthlyInterestRate() {
		return annualInterestRate/12;
	}
//define method withdraw
	double withdraw(double amount) {
		return balance -= amount;
	}	
//define method deposit
	double deposit(double amount) {
		return balance += amount;
	}
}

Ok I understand.

Hi first post here and am new to java. I'm teaching myself by working through the textbook that this problem comes from. It looks like your main problem here is that your not assigning a value to the dateCreated Date object in your no arg constructor (or the arg constructor for that matter). Also the assignment doesn't require a mutator method for the Date object (setDate), since this would give people the ability to tamper with the created Account in a manner that isn't wanted (assignment only asks for accessor method for dateCreated). All the data fields that have default values can be assigned in the data section at the top of the class and don't need to be set in the no arg constructor but that doesn't really matter I guess (you can do it in constructor if you want). Here's how I created Account class. I've included some comments inside the code to point out the problems and my thinking...

import java.util.Date;
 
public class Account {
	// Private data fields for Account object
	private int id = 0; // Assign default value
	private double balance = 0; // Assign default value
	private double annualInterestRate = 0; // Assign default value
	private Date dateCreated; // Here I'm just letting the compiler know there is a Date object associated with each Account object 
                                            // but no value for this object is referenced; value referenced when Account object is created by constructors
 
	// no arg Constructor for Account
	public Account() {
		dateCreated = new Date(); // Here is where I believe you go wrong, create Date object when Account object is created (new Date())
                                                     // and assign it's reference to dateCreated, this is why you're getting null returned.
                                                     // You've got a Date object but it never gets a reference to any actual data.
                                                     // What you've done is sort of like creating an Array object but not populating it with data; basically a
                                                     // shortcut that doesn't point to anything hence null, empty.
                                                     // Also note that I don't have to assign default values for other data fields since I assigned them above.
	}
 
	// Constructor with id and balance args
	public Account(int newID, double newBalance) {
		dateCreated = new Date(); // And again for argument constructor
		id = newID;
		balance = newBalance;
	}
 
	// Accessor method for id
	public int getID() {
		return id;
	}
 
	// Mutator method for id
	public void setID(int newID) {
		id = newID;
	}
 
	// Accessor method for balance
	public double getBalance() {
		return balance;
	}
 
	// Mutator method for balance
	public void setBalance(double newBalance) {
		balance = newBalance;
	}
 
	// Accessor method for annualInterestRate
	public double getAnnualInterestRate() {
		return annualInterestRate;
	}
 
	// Mutator method for annualInterestRate
	public void setAnnualInterestRate(double newAnnualInterestRate) {
		annualInterestRate = newAnnualInterestRate;
	}
 
	// Accessor method for dateCreated; NOTE: no mutator method for dateCreated required...
	public Date getDateCreated() {
		return dateCreated;
	}
 
	// Method for returning monthlyInterestRate calculated from annualInterestRate
	public double getMonthlyInterestRate() {
		return annualInterestRate/12;
	}
 
	// Method for withdrawing specified amount
	public void withdraw(double withdrawAmount) {
		balance -= withdrawAmount;
	}
 
	// Method for depositing specified amount
	public void deposit(double depositAmount) {
		balance += depositAmount;
	}
}

And here's the test method to show it works.

public class Exc87 {
 
	public static void main(String[] args) {
		Account test = new Account(1122, 20000);
		test.setAnnualInterestRate(4.5);
		test.withdraw(2500);
		test.deposit(3000);
		System.out.printf("The current balance is $%1.2f.\n", test.getBalance());
		System.out.println("The monthly interest is " + test.getMonthlyInterestRate() + "%.");
		System.out.println("The account was created on " + test.getDateCreated().toString() + ".");
 
	}
 
}

Happy coding

Yeah mostly posted because I came across it while trying to do same exercise, it helped me with a problem or two I had but seemed like it could use a little more explanation for beginners like me since that is who mostly will be doing this problem, it's from chapter 8 of an introduction to java book. I know the original poster has moved on and finished by now but I thought it might help others like me work through the problem. LOL sorry but ease up it's my 1st post

Originally Posted by MasterCylinder

I know the original poster has moved on and finished by now but I thought it might help others like me work through the problem.)

I'm glad you posted, I was also assigned this problem and stumbled across this post when trying to figure out if I was doing my getter and setter methods correctly. I was glad to see your example of the test program since I'm working on one of these as weell and was kind of confused as to how it works. I'm new here too and still really new to Java in general, so I really appreciate people posting their input on things like these even if it's an old post. Like you said, even if the OP has figured it out and moved on, there could still be others out there come across it later and find your answer handy. :-)