Sams Teach Yourself Java™ in 24 Hours (Covering Java 7 and Android)

ptg7068951

122 HOUR 10:Creating Your First Object

Each object has things that make it different than other objects. Pie charts

are circular, whereas bar graphs represent data as a series of rectangles. If

you break down computer programs in the same way a pie chart is broken

down, you’re engaging in OOP. In OOP, an object contains two things:

attributes and behavior. Attributesare things that describe the object and

show how it is different than other objects. Behavioris what an object does.

You create objects in Java by using a class as a template. Aclassis a master

copy of the object that determines the attributes and behavior an object

should have. The term classshould be familiar to you because Java pro-

grams are called classes. Every program you create with Java is a class that

you can use as a template for the creation of new objects. As an example,

any Java program that uses strings is using objects created from the String

class. This class contains attributes that determine what a Stringobject is

and behavior that controls what Stringobjects can do.

With OOP, a computer program is a group of objects that work together to

get something done. Some simple programs might seem as though they

consist of only one object: the class file. However, even those programs are

using other objects to get work done.

Objects in Action

Consider the case of the program that displays a pie chart. APieChart

objectcould consist of the following:

. Behavior to calculate the size of each pie slice
. Behavior to draw the chart
. An attribute to store the title of the chart

Bangladesh

India

Indonesia

China

United States

Pakistan

Brazil

Nigeria

Russia

Japan

FIGURE 10.1
A Java program that displays a pie
chart.