- Overall Application
- Ferret Interface
- Implementing the Ferret
- Instantiating the Ferret
- A Second Ferret
- Introducing the Factory
- Enabling the Factory to Use Different Classes
- Allowing the User to Choose at Runtime
- Moving On from Here
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Enabling the Factory to Use Different Classes
Now that we've got the factory working, let's enable it to use different classes. One way to do that is to create a version of newFerret() that takes a class name and then dynamically instantiates that class.
NOTE
Dynamic class creation is a topic unto itself. For more information on creating classes dynamically and using introspection, check out
http://developer.java.sun.com/developer/technicalArticles/ALT/Reflection/.
First, we create a new method in the FerretFactory, as shown in Listing 8.
Listing 8 Taking In a Class Name
package org.chase.research;
public class FerretFactory {
public Ferret newFerret() {
return new org.chase.ferrets.GoogleFinder();
}
public Ferret newFerret (String classname) {
Ferret theFerret = null;
try {
theFerret = (Ferret) Class.forName(classname).newInstance();
} catch (Exception e) {
theFerret = new org.chase.ferrets.GoogleFinder();
}
return theFerret;
}
}
In this case, if the newFerret() method has an argument, the factory will try to create a class by that name, cast it as a Ferret, and return it. If there are any problems creating a class by that name—if the class doesn't exist, for example—the method just returns a GoogleFinder-variety Ferret.
Now, the application can be run exactly as it was by using a GoogleFinder, or we can specifically request a GoogleSpecificFinder, as shown in Listing 9.
Listing 9 Requesting a Specific Class
...
String searchTerm = args[0];
FerretFactory ferretFactory = new FerretFactory();
Ferret theFerret = ferretFactory.newFerret(
"org.chase.ferrets.GoogleSpecificFinder");
System.out.println("Getting Results ...");
...
Now, if we run the application, we'll see the more sleek GoogleSpecificFinder-variety of results.
We could, in fact, add any class name here, as long as that class existed and implemented the Ferret interface.
But it still ties the application to a specific implementation of Ferret.