1. JAVA CLASSES

2. Class Definition: accessSpecifier class ClassName fields constructors{
fields
constructors
methods }
Attributes of the object
Initialization of the object
Actions on the object

3. Choose a name for a program that simulates a bank account:
public class BankAccount {
fields
constructors
methods }
We will be able to create objects of type BankAccount

4. Instance Fields An object stores its data in instance fields
Field: a technical term for a storage location inside a block of memory
Instance of a class: an object of the class
The class declaration specifies the instance fields:

5. access specifier nameOfVariable
Instance Field Syntax
An instance field declaration consists of the following parts:
access specifier (such as private, public or protected)
type of variable (such as double, int, String)
name of variable (such as balance)
Each object of a class has its own set of instance fields
You should declare all instance fields as private
access specifier nameOfVariable

6. Create a field to store a bank account holder’s balance
public class BankAccount {
private double balance;
constructors
methods }

7. private double balance; private int accountNumber; constructors
Suppose we modify the BankAccount class so that each bank account has an account number. How does this change/affect the instance fields?
public class BankAccount {
private double balance;
private int accountNumber;
constructors
methods }

8. Static Fields private double balance; private int accountNumber;
A static field belongs to the class, not to any object of the class. Also called class field.
public class BankAccount {
private double balance;
private int accountNumber;
private static String bankName = “McLees Money”; }
If bankName was not static, each instance of BankAccount would have its own bank name

9. Static Fields Static fields should always be declared as private
Exception: Static constants, which may be either private or public
public class BankAccount {
public static final double OVERDRAFT_FEE = 5;
/* Refer to it as BankAccount.OVERDRAFT_FEE */ }

10. Fields for the BankAccount class
public class BankAccount {
private double balance;
private int accountNumber;
private static String bankName = “McLees Money”;
public static final double OVERDRAFT_FEE = 5;
constructors
methods }

11. Methods Three Types: Accessor – gets information to the user Mutator-
Behaviors or actions taken on an object of a class
Three Types:
Accessor –
gets information to the user
Mutator-
changes or alters one of the fields of an object
Helper-
aids the program in solving problems…
usually done behind the scenes

12. What are the behaviors of a BankAccount object?
mutator
deposit money
This method will add an amount to the balance in account
withdraw money
This method will add an amount to the balance in account
mutator
Accessor
get balance
This method will get the balance in account and return it
to the user

13. Method Syntax: a method header consists of the following parts:
access specifier (such as private, public)
return type of variable (such as double, int, String, void)
method name of variable (such as deposit)
list of incoming variables (parameters ) including their type
method body in { }
access specifier return type nameOfMethod (dataType paramterName) {
method body; }

14. Methods for the BankAccount class
public class BankAccount {
fields
constructors
public void deposit (double amount){ … }
public void withdraw(double amount){ … }
public double getBalance() {…} }

15. Methods for the BankAccount class let’s add another Helper method to compute the overdraft fee
public class BankAccount {
fields
constructors
public void deposit (double amount){ … }
public void withdraw(double amount){ … }
public double getBalance() {…}
private double overdraftFee() {…} }

16. Constructors: A constructor initializes an instance field
Three types of constructors
Default-sets all the instance fields to their default values
Numbers = 0, Strings = null, booleans = false
Overloaded - sets the instance fields to user input
Copy-uses a prewritten constructor to initialize other objects
Constructor name = class name
Constructor body is executed when a new object is created
All the constructors will have the same name-only the parameters are different (computer can tell the difference)
Constructors for us are always public

17. Constructor Syntax: public NameOfClass (dataType paramterName) {
access specifier (public)
name of Class (such as BankAccount)
list of parameters, including their data type for overloaded constructors
constructor body in { }
public NameOfClass (dataType paramterName) {
constructor body; }

18. Constructors for the BankAccount class
public class BankAccount {
private double balance;
private int accountNumber;
private static String bankName = “McLees Money”;
public static final double OVERDRAFT_FEE = 5;
public BankAccount ( )
balance = 0;
accountNumber = 0; }
public BankAccount (double myBalance, int myAcctNum)
balance = myBalance;
accountNumber = myAcctNum;
methods

19. Public Interface for the BankAccount class
public class BankAccount { private double balance; private int accountNumber; private static String bankName = “McLees Money”; public static final double OVERDRAFT_FEE = 5; public BankAccount ( ) balance = 0; accountNumber = 0; } public BankAccount (double myBalance, int myAcctNum) balance = myBalance; accountNumber = myAcctNum; public void deposit (double amount){ … } public void withdraw(double amount){ … } public double getBalance() {…} private double overdraftFee() {…}