Why are these variables of an interface type not being used to instantiate new objects?
<p>I'm using <a href="http://javadoc.jlibav.googlecode.com/git/index.html" rel="nofollow">this</a> api and have come across some a code example that is confusing me. I know that I can assign an object to an interface using "new", since an interface is a datatype. What I don't understand from the code below is why the variables: "cc" and "audioDecoder" are assigned the values that they have been assigned. As far as I know, those variables should be assigned to new objects. Could someone explain what is going on here? </p>

<pre><code>try {
// open media file 
DefaultMediaPlayer player = new DefaultMediaPlayer("/home/me/walking.wav");

// get some properties of the first audio stream 
IDecoder audioDecoder = player.getAudioStreamDecoder(0);
ICodecContextWrapper cc = audioDecoder.getCodecContext();

int sampleFormat = cc.getSampleFormat();
int sampleRate = cc.getSampleRate();
int bytesPerSample = AVSampleFormat.getBytesPerSample(sampleFormat);
long channelLayout = cc.getChannelLayout();
int channelCount = AVChannelLayout.getChannelCount(channelLayout);
AudioFormat.Encoding encoding;

if (AVSampleFormat.isPlanar(sampleFormat) || AVSampleFormat.isReal(sampleFormat))
    throw new LibavException("unsupported output sample format");
else if (AVSampleFormat.isSigned(sampleFormat))
    encoding = AudioFormat.Encoding.PCM_SIGNED;
else
    encoding = AudioFormat.Encoding.PCM_UNSIGNED;

// create Java InputStream for audio stream raw data
SampleInputStream sis = new SampleInputStream(sampleRate * bytesPerSample * channelCount, true);

// create AudioInputStream from the SampleInputStream
AudioInputStream audioStream = new AudioInputStream(sis, new AudioFormat(encoding, sampleRate,
    bytesPerSample * 8, channelCount, bytesPerSample * channelCount, sampleRate, 
    ByteOrder.BIG_ENDIAN.equals(ByteOrder.nativeOrder())), -1);

// create adapter between Libav audio frames and the SampleInputStream
Frame2AudioFrameAdapter resampler = new Frame2AudioFrameAdapter(channelLayout, channelLayout, sampleRate, 
    sampleRate, sampleFormat, sampleFormat);

// get audio mixer for the audio stream format
PlaybackMixer audioMixer = PlaybackMixer.getMixer(audioStream.getFormat());

// connect all streams
audioDecoder.addFrameConsumer(resampler);
resampler.addAudioFrameConsumer(sis);
audioMixer.addInputStream(audioStream); 

// enable audio stream decoding
player.setAudioStreamDecodingEnabled(0, true);

// start playback
audioMixer.play();
player.play();

// wait until the playback stops
player.join();

// release system resources
player.close();
resampler.dispose();
PlaybackMixer.closeAllMixers();
} catch (Exception ex) {
    Logger.getLogger(PlaybackSample.class.getName()).log(Level.WARNING, "unable to play audio", ex);
}
</code></pre>
