Rethinking the Jukebox Program

• Last quarter, the final assignment was to make a Jukebox interface.
• There are many ways to do this.  As you may recall, I gave extra credit if you were able to write the entire program without using an if test.  One way to do that is with one listener for each type of music.
• We can do the same thing with only one listener, and a factory.
• Each JRadioButton has the same listener attached.
• The listener gets the label from the JRadioButton, and passes it to a factory method.
• The factory method then returns an instance of that subclass.
• We need to introduce a few new concepts to make this work.
• First, we still need to know what song type the user clicked.  We can get this from the Event object that we pass to the listening method - evt.getSource() will return an instance of the calling object.
• Then, we need to cast that to a JRadioButton type, since a JRadioButton initiated that event.
• Now, we need to get the text label out of that JRadioButton so that we know what the user clicked.  We can use the getLabel() method of the JRadioButton class.
• Once we know the label of the button that the user clicked, we can pass that to our factory method, songFactory(String songType).
• Our factory method can instantiate that class dynamically.  The Class class has a method, getClass, that will get a class based on the String passed to it.  newInstance() will actually create a new object instance of that class.
• We cast that object to a Song type and return it.
• Using getClass() and newInstance requires a try-catch block, which we'll cover later today.
• Take a look at the original source of all classes used.
• Take a look at the new source with the factory method.  Changed text in green.  Only the Jukebox class changed.
• What kind of class diagram would you draw for this?

Created by:  Brandan Jones December 17, 2001