OBJECTS AND CLASSES - Introduction to Java Programming - page 298

UML Class Diagram Circle Class name

Data fields

radius: double

Circle()
Circle(newRadius: double)
getArea(): double
getPerimeter(): double
setRadius(newRadius: double): void

Constructors and
methods

UML notation
for objects

circle1: Circle circle2: Circle circle3: Circle

radius = 1

radius = 25 radius = 125

F IGURE 8.4

Classes and objects can be represented using UML notation.

The method is denoted as
methodName(parameterName: parameterType): returnType
8.3 Example: Defining Classes and Creating Objects
Classes are definitions for objects and objects are created from classes.

Key
Point

This section gives two examples of defining classes and uses the classes to create objects.
Listing 8.1 is a program that defines the Circle class and uses it to create objects. The pro-
gram constructs three circle objects with radius 1 , 25 , and 125 and displays the radius and
area of each of the three circles. It then changes the radius of the second object to 100 and dis-
plays its new radius and area.

Note
To avoid a naming conflict with several enhanced versions of the Circle class intro-
duced later in the chapter, the Circle class in this example is named SimpleCircle .
For simplicity, we will still refer to the class in the text as Circle .
L ISTING 8.1 TestSimpleCircle.java
1

avoid naming conflicts

public class TestSimpleCircle {

main class

2 /** Main method */

3 public static void main(String[] args) {

main method

4 // Create a circle with radius 1

5
6 System.out.println( "The area of the circle of radius "
7 +

SimpleCircle circle1 = new SimpleCircle();

create object

circle1.radius + " is " + circle1.getArea() );

8
9 // Create a circle with radius 25

SimpleCircle circle2 = new SimpleCircle( 25 );

10
11 System.out.println( "The area of the circle of radius "
12 + circle2.radius + " is " + circle2.getArea());
13
14

create object

// Create a circle with radius 125

15
16 System.out.println( "The area of the circle of radius "
17 + circle3.radius + " is " + circle3.getArea());
18
19 // Modify circle radius
20 // or circle2.setRadius(100)
21 System.out.println( "The area of the circle of radius "
22 +

SimpleCircle circle3 = new SimpleCircle( 125 );

create object

circle2.radius = 100 ;

circle2.radius circle2.getArea()

+ " is " + );

23 }