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* @param amt the amount to be withdrawn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* @param amt the amount to be withdrawn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