1. Introduction to Objects & Classes
Paul Bui

2. Introduction
Group related information and methods (functions) together
Design classes with attributes and behaviors in mind
Circle Example
Attributes?
Behaviors?

3. Building a Class - Attributes
Name the java file the same name as the class (e.g. Circle.java)
Capitalize the class name
Put the attributes at the top of the class and make them private
It’s nice to give them default values too (e.g. radius = 0.0)
public class Circle {
private double radius = 0.0;
... }

4. Building a Class - Constructors
Used when the object is instantiated
String str = new String();
No return type
Always has the same name as the class
Can have 0 or more parameters
Two types:“default constructor” and “specific constructors”
Example:
public Circle() // “default constructor” has 0 parameters { }

5. Building a Class - Constructors
“specific constructor” takes parameters that set the attributes
Example:
public Circle(double newRadius) {
radius = newRadius; }

6. Building a Class - Methods
Methods are defined and declared using the following template:
public RETURNTYPE METHODNAME(PARAMETERS) {
//METHOD CODE }
Example:
public double getArea()
return *radius*radius;

7. Naming Methods Naming Methods Parts of a method
Capitalize every word in the method name EXCEPT for the first
Example: thisIsAGoodMethodName()
No spaces in the method name
Parts of a method
All methods except for the constructors have the same form
RETURNTYPE METHODNAME ( PARAMETERS )

8. Methods – Getters & Setters
Accessors (Getters)
Used to access attributes
0 parameters
Example
public double getRadius() {
return radius; }

9. Methods – Getters & Setters
Mutators (Setters)
Used to change attributes
Most of the time has a return type of void
Example
public void setRadius(double newRadius) {
radius = newRadius; }

10. Access Levels
Controls whether or not the attribute or method can be seen/used outside of the class
public, private, protected
Put in front of class name, attributes, and methods