Designing and Implementing a Class

Step 1

�Determine how clients will use your class. To do this, consider writing a test class:

public class AccountTester {
�� public static void main(String[] args) {
����� Account savings = new Account(500.25);
����� Account checking = new Account();
����� savings.withdraw(200);
����� checking.deposit(200);
����� double bal = savings.getbalance();
����� // this should print $300.25:
����� System.out.println("savings = $" + bal);
�� }
}

Step 2

Design the public interface for your class:

public class Account {
�� public Account() {

�� }
�� public Account(double initBalance) {

�� }
�� public void withdraw(double amt) {

�� }
�� public void deposit(double amt) {

�� }
�� public double getbalance() {
����� return 0; // for now
�� }
} // end class Account

Step 3

Add javadoc comments:

/**
�* Instances of this class represent bank accounts
�*
�* @author Pearce
�* @version 1.0
�*/
public class Account {
�� /**
��� * Creates an account with balance = $0
��� */
�� public Account() {

�� }
�� /**
��� * Creates an account with a specified balance
��� *
��� * @param initBalance the initial balance
��� */
�� public Account(double initBalance) {

�� }
�� /**
��� * Reduces the balance by the specified amount
��� *
��� * @param amt the amount to be withdrawn
��� */
�� public void withdraw(double amt) {

�� }
� �/**
��� * Increments the balance by the specified amount
��� *
��� * @param amt the amount to be deposited
��� */
�� public void deposit(double amt) {

�� }
�� /**
��� * returns the current balance
��� *
��� * @returns the current balance
��� */
�� public double getbalance() {
����� return 0; // for now
�� }
} // end class Account

Step 4

Add the fields:

/**
�* Instances of this class represent bank accounts
�*
�* @author Pearce
�* @version 1.0
�*/
public class Account {
�� private double balance;
�� /**
��� * Creates an account with balance = $0
��� */
�� public Account() {

�� }
�� /**
��� * Creates an account with a specified balance
��� *
��� * @param initBalance the initial balance
��� */
�� public Account(double initBalance) {

�� }
�� /**
��� * Reduces the balance by the specified amount
��� *
��� * @param amt the amount to be withdrawn
��� */
�� public void withdraw(double amt) {

�� }
�� /**
��� * Increments the balance by the specified amount
��� *
��� * @param amt the amount to be deposited
��� */
�� public void deposit(double amt) {

�� }
�� /**
��� * returns the current balance
��� *
��� * @returns the current balance
��� */
�� public double getbalance() {
����� return 0; // for now
�� }
} // end class Account

Step 5

Implement the constructors and methods:

/**
�* Instances of this class represent bank accounts
�*
�* @author Pearce
�* @version 1.0
�*/
public class Account {
�� private double balance;
�� /**
��� * Creates an account with balance = $0
��� */
�� public Account() {
����� balance = 0;
�� }
�� /**
��� * Creates an account with a specified balance
��� *
��� * @param initBalance the initial balance
��� */
�� public Account(double initBalance) {
����� balance = initBalance;
�� }
�� /**
��� * Reduces the balance by the specified amount
��� *
��� * @param amt the amount to be withdrawn
��� */
�� public void withdraw(double amt) {
����� // if funds available
����� balance = balance � amt;
�� }
�� /**
��� * Increments the balance by the specified amount
��� *
��� * @param amt the amount to be deposited
��� */
�� public void deposit(double amt) {
����� // if 0 <= amt
����� balance = balance + amt;
�� }
�� /**
��� * returns the current balance
��� *
��� * @returns the current balance
��� */
�� public double getbalance() {
����� return balance;
�� }
} // end class Account

Step 6

Test, test, test