Cast error in java sound

Question

Hey, i got a little run-time error:
Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: com.sun.media.sound.PortMixer$PortMixerPort
the code segment it occurs at is here:
case 0:
      targetDataLine1 = (TargetDataLine)mixer1.getLine(targetInfo);
      targetDataLine2 = targetDataLine1;
}Some background info: I used getTargetLines() method of Mixer to obtain an arraylist of all the Line.Info objects (for targetLines) in a mixer, then I passed this into a GUI class, and made a vector to display in combo box. once user selects an item, it casts it back into Line.Info, and calls the mixer's "getLine()" method to retrieve the line. But I get the cast error. I know you can cast from Line to TargetDataLine (since TargetDataLine is a subinterface of Line) -- and I saw it on a tutorial, so I don't know what's wrong. Any help?
If you need more info, just tell me.

Answer 1

But still, the tutorial I looked at
(http://java.sun.com/j2se/1.5.0/docs/guide/sound/progr
ammer_guide/chapter3.html#113154)
still showed it down-casting from a Line object to a
TargetDataLine object.
You need to understand the difference between a reference and an object. The object itself was a TargetDataLine object, otherwise the cast wouldn't have worked. The reference to it was of type Line.
// obj is a reference of type Object. The object it points to is a String:
Object obj = "I am a String";
// Which explains why this works:
String s = (String)obj;
// and why this fails:
Integer i = (Integer)obj;
Not to mention, the java API says that the
getLine(Line.Info) object returns an object of type
Line.
And I still don't understand why you can't cast from
a superclass to a subclass. I know intuitively, it
makes since, since not all RECTANGLES are SQAURES,
but all SQUARES are RECTANGLES. But still, I know
enough programming to remember numerous instances of
casting Object as other classes....
See above.
Oh, and what does the $ symbol in
com.sun.media.sound.PortMixer$PortMixerPort mean?It means that the the class PortMixerPort is an inner class (or nested class, I never remember the difference :-) in the class PortMixer.