1. Classes Variables That Are Not of a Built-in Type Are Objects
A Class Is an Object Type
A Class Represents a “Thing” (e.g., employee, wrench, list, store, shopping cart, etc.)
Service Class – Class used by Other Programs
Must Be Created in ClassName.java File

2. Generic Object Declaration
class useObject {
public static void main(String [ ] args)
Object varName = new Object();//instance
varName.objectMethod(); //invoke method }}
Instance of Object Type Is Called Invoking Object of Class Methods
varName is an instance of Object
varName is invoking object of objectMethod()

3. Creating a Class Programmers Define Classes with: Methods
Data Members (or Fields, Attributes)
Used to store information about each object
Each member is a variable of some other type
Methods
Used to give programmers access to object

4. Designing a Class Decide How It Will Be Used
Decide on Interface (i.e., public representation, public methods)
Decide on Implementation (i.e., private data and data manipulation)
Example: String Methods (interface) includes length(), toUpper(), toLower(), charAt(), etc.
Example: String Implementation includes (*probably*) char variables to hold characters, integer to hold length (we don’t actually need to know)

5. Constructor Class Method of Same Name
Example: class Employee Method Employee()
Called When Variable Declared (instantiated) of Class Type
Initializes Instantiated Object
May Have Multiple Constructors Each with Different Parameters

6. Access Modifiers Used to Identify What May Use Methods
public – any method may use
private – only methods in same class may use
protected – only methods in same class or related classes may use.

7. Example: Class Employee
Employee emp1;
String firstName;
String lastName;
double salary;
First and last names and salaries are data members, or fields or
attributes.

8. //Employee.java file
class Employee {
private String firstName;
private String lastName;
private double salary;
private final double MAXSALARY = ;
public Employee()
{ // access to invoking object attributes
firstName = "NoFirstName";
lastName = "NoLastName";
salary = 0.0; }

9. Employee Declaration Employee emp1 = new Employee();
Main Memory (allocated by “new”, initialized by Employee() )
emp1
String firstName;
"NoFirstName"
String lastName;
"NoLasttName"
double salary;
0.0

10. Client Program A Program that Uses a Class Is a Client of that Class
Class Objects are Declared and Instantiated Using the new keyword.
new ClassName(parameters) Calls Constructor for Class
Class Public Methods Called Using Dot (e.g., variable.GetName();)

11. Client Test Program class useEmployee {
public static void main(String [ ] args)
Employee emp1 = new Employee(); }

12. Accessor Methods
Public Methods for Getting Attributes of Class

13. public String GetFirstName() return firstName;
class Employee {
private String firstName;
private String lastName;
private double salary;
private final double MAXSALARY = ;
public Employee()
firstName = "NoFirstName";
lastName = "NoLastName";
salary = 0.0; }
public String GetFirstName()
return firstName;
public String GetLastName()
return lastName;
public double GetSalary()
return salary;

14. class useEmployee {
public static void main(String [ ] args)
Employee emp1 = new Employee();
System.out.println("Name is" + emp1.GetFirstName() + " " + emp1.GetLastName()); }

15. Mutator Methods
Class Methods Used to Modify a Class Object are Called Mutator Methods
Allows Restricted Manipulation of Class Object Data

16. public boolean SetSalary(double passedSalary){
if (passedsalary <= MAXSALARY)
salary = passedSalary;
return true; }
else
return false;

17. class useEmployee { public static void main(String [ ] args)
Employee emp1 = new Employee();
System.out.println("Name is" + emp1.GetFirstName() + " " + emp1.GetLastName());
if (emp1.SetSalary(55000))
System.out.println("Salary set to 55000"); }
else
System.out.println("Salary not set");

18. Exam 2 EXAM 2 Monday in Lecture!!! 20% of Final Grade Know:
loops, switch/case
Files
Input failure (e.g. scan.hasNextInt())
Methods
Classes
Everything Through Lecture Wednesday