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Title |
How Polymorphism works.
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Summary |
A simple example of Polymorphism using extends. As usual this is done using the animal sound example. |
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Contributor |
John McTainsh
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Published |
25-Oct-2000 |
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Last updated |
25-Oct-2000 |
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Description.
Polymorphism simply means creating an object with different forms. This
is useful when modeling real world items in software. For example a car
is a basic object but it can have many forms such as "Toyota", "Ford" and "Lada".
How to use it.
The following code demonstrates this by creating a base object, CAnimal as follows;
//This is an abstract (base) class that all the amimals must support
abstract class CAnimal
{
public abstract void WhatAreYou();
public void Speak()
{
System.out.print( "Quite" );
}
}
Note CAnimal uses the keyword abstract to indicating this is a base
class and cannot use to create an object directly. The WhatAreYou();
has not body and MUST be declared in all classes that are derived from it. The classes
below are derived from the CAnimal class.
//This snake overides name and sound
class CSnake extends CAnimal
{
public void WhatAreYou()
{
System.out.print( "Snake" );
}
public void Speak()
{
System.out.print( "Sssssss" );
}
}
//Monkey overides name but uses the default sound
class CMonkey extends CAnimal
{
public void WhatAreYou()
{
System.out.print( "Monkey" );
}
}
See how CSnake overides the Speak() method also. Now
lets put it all together.
///////////////////////////////////////////////////////////////////////////////
// Program demonstrates a single class having diferent forms.
public class Polymorph
{
// The main entry point for the application.
// @param args Array of parameters passed to the application
public static void main (String[] args)
{
System.out.println( "Starting Polymorph application" );
//Initialize array of zoo animals
CAnimal zoo[] = new CAnimal[2];
zoo[0] = new CMonkey();
zoo[1] = new CSnake();
//Output results
for( int n = 0; n < zoo.length; n ++ )
{
zoo[n].WhatAreYou();
System.out.print( " says " );
zoo[n].Speak();
System.out.println( "." );
}
System.out.println( "Terminating Polymorph application!" );
}
}
The above code will give the following output.
Starting Polymorph application
Monkey says Quite.
Snake says Sssssss.
Terminating Polymorph application!
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