1. Tonga Institute of Higher Education
Creating Classes
Tonga Institute of Higher Education

2. Introduction
The main method contains the code that is started when the application is first executed.
Until now, we have always used objects that use the main method.
But, many objects do not need the main method.
Any class that does not need to be started when the application is first executed does not need a main method.

3. Custom Classes and Objects
Sometimes, the objects we have do not fit our needs.
We can define custom objects.
We can use custom objects just like normal objects

4. Drivers
Any class that does not have the main method cannot start by itself
Often, developers make tools so they can test their class.
A driver is a tool used to begin a program
They are useful when testing objects

5. Demonstration
StudentDriver

6. Create Our First Class Our class will be a student Each student has a:
School
First Name
Last Name
Program
Age
Gender

7. Demonstration
Student

8. How to Define a Class Special Access Specifier Keyword Class Name
public class Customer {
//Body of Class }
Access Specifier
Class Name
Special
Keyword

9. Access Specifiers Default – This can be used by:
public class Customer {
//Body of Class }
Access Specifier
Class Name
Special
Keyword
Default – This can be used by:
Code in classes in the same package
Public – This can be used by everything:
Code in classes in different packages

10. Special Keyword and Class Name
public class Customer {
//Body of Class }
Access Specifier
Class Name
Special
Keyword
Keyword
Must always be class
Class Names
Class names should be nouns
One word
The first letter is capitalized.
The first letter of each internal word is capitalized.
Keep your class names simple and descriptive.
Example:
Customer
SalesOrder

11. Constructors
Constructor – A method that is automatically executed when an object is created.
This allows you to set initial values for the object.
Many objects have multiple constructors. (They are overloaded)
You can find a list of constructors in the Java Developer’s Kit documentation.
Show Java Doc

12. Default Constructors All classes have a default constructor
The default constructor is a constructor that accepts no parameters
Automatically called when the object is created
Default constructors go away when you define your own constructors

13. Creating Constructors
Constructors are methods that have the same name as the class
Constructors do not return anything but do not include the word void.
To overload constructors
Define multiple methods with the same name as the class with different parameters
Same name as class
Overloaded

14. FavoriteFoods and FavoriteFoodsDriver
Demonstration
FavoriteFoods and FavoriteFoodsDriver

15. Garbage Collection When we create objects, we use memory space.
If we never destroy objects, our computer will run out of memory and crash.
Fortunately, the Java Garbage collector automatically destroys data.
It runs behind the scenes and destroys an object when it detects an object that is no longer used by the program.

16. Finalizers
Finalizer – A method that is automatically executed when an object is destroyed.
public void finalize() {
//Body of method }