Prentice.Hall.Introduction.to.Java.Programming,.Brief.Version.9th.(2014).[sharethefiles.com]

298 Chapter 8 Objects and Classes
UML Class Diagram
Circle
radius: double
Circle()
Circle(newRadius: double)
getArea(): double
getPerimeter(): double
setRadius(newRadius: double): void
Class name
Data fields
Constructors and
methods
circle1: Circle
radius = 1
circle2: Circle
radius = 25
circle3: Circle
radius = 125
UML notation
for objects
Key
Point
FIGURE 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.
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 program
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 displays
its new radius and area.
avoid naming conflicts
main class
main method
create object
create object
create object
LISTING 8.1
Note
To avoid a naming conflict with several enhanced versions of the Circle class introduced
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.
TestSimpleCircle.java
1 public class TestSimpleCircle {
2 /** Main method */
3 public static void main(String[] args) {
4 // Create a circle with radius 1
5
6
SimpleCircle circle1 = new SimpleCircle();
System.out.println("The area of the circle of radius "
7 + circle1.radius + " is " + circle1.getArea() );
8
9 // Create a circle with radius 25
10
11
SimpleCircle circle2 = new SimpleCircle(25);
System.out.println("The area of the circle of radius "
12 + circle2.radius + " is " + circle2.getArea());
13
14 // Create a circle with radius 125
15
16
SimpleCircle circle3 = new SimpleCircle(125);
System.out.println("The area of the circle of radius "
17 + circle3.radius + " is " + circle3.getArea());
18
19 // Modify circle radius
20 circle2.radius = 100; // or circle2.setRadius(100)
21 System.out.println("The area of the circle of radius "
22 + circle2.radius + " is " + circle2.getArea() );
23 }