Sams Teach Yourself C in 21 Days

22: System.out.println(“ The name is “ + c3.name);

23: }

24: }

For c1:

The radius is 0.0

The name is Unnamed

For c2:

The radius is 99.99

The name is Unnamed

For c3:

The radius is 0.0010

The name is Harold

In the code for the circleclass, lines 5 and 6 declare the class’s two properties.

Lines 8 to 11 define a constructor that takes no arguments, and the code here ini-

tializes the two properties to their default values. Lines 13 to 16 define a constructor that

takes a single type doubleargument, and code in this constructor initializes the radius

property to this value and the nameproperty to the default value. Lines 18 to 21 define a

third constructor, this time taking two arguments—one type doubleand one type String.

Code in this constructor uses the argument values to initialize the class’s two properties.

The demonstration program in Listing B5.10 creates three instances of the circleclass.

Lines 7 to 9 declare the variables that will hold the object references. Line 11 creates a

new instance passing no arguments, so the class’s first constructor will be called. Lines

12 and 13 create other instances of the class, passing one and two arguments respec-

tively. The remaining lines of code display the property values of the three circle

objects so you can see that the values were initialized properly.

Using Inheritance ................................................................................................

Inheritance is one of the most powerful features of Java and other object-oriented pro-

gramming languages. Inheritance lets you create a new class not from scratch, but based

on an existing class. When you do this, the new or childclass automatically has, or

inherits, all the properties and methods of the original or parentclass (sometimes called

thesuperclass). Then, you can add new properties and methods to the child class, or you

can create replacements for properties and methods from the parent class.

Let’s look at a hypothetical example. Suppose you are writing a program to perform

financial calculations. You have a class that performs just about all the needed calcula-

tions—car payments, mortgages, and so forth—but omits one thing that you want to

include in your program, lease payments. Do you need to start from scratch and create a

736 Bonus Day 5

LISTINGB5.10 continued

OUTPUT

ANALYSIS

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