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POA couple of questions about a music project in Java
 

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  1. POA couple of questions about a music project in Java
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    <p>I have a couple of questions about a school project I'm working on. The code is as follows.</p> <pre><code>public class Player { private PlayList playList; private Track track; private int tracksPlayed; private int totalTrackTime; private double averageTrackTime; /** * Constructor ... */ public Player() { playList = new PlayList("audio"); track = playList.getTrack(0); this.tracksPlayed = tracksPlayed; this.totalTrackTime = totalTrackTime; this.averageTrackTime = averageTrackTime; } /** * Return the track collection currently loaded in this player. */ public PlayList getPlayList() { return playList; } /** * */ public void play() { track.play(); tracksPlayed++; int trackDuration = track.getDuration(); totalTrackTime = totalTrackTime + trackDuration; averageTrackTime = totalTrackTime / tracksPlayed; } /** * */ public void stop() { track.stop(); } /** * */ public void setTrack(int trackNumber) { int currentTrack = trackNumber; track = playList.getTrack(currentTrack); } /** * */ public String getTrackName() { String currentTrack = track.getName(); return currentTrack; } /** * */ public String getTrackInfo() { String currentTrack = track.getName(); int trackDuration = track.getDuration(); return currentTrack + " " + "(" + trackDuration + ")"; } /** * */ public int getNumberOfTracksPlayed() { return tracksPlayed; } /** * */ public int getTotalPlayedTrackLength() { return totalTrackTime; } /** * */ public double averageTrackLength() { return averageTrackTime; } } public class Track { private Clip soundClip; private String name; /** * Create a track from an audio file. */ public Track(File soundFile) { soundClip = loadSound(soundFile); name = soundFile.getName(); } /** * Play this sound track. (The sound will play asynchronously, until * it is stopped or reaches the end.) */ public void play() { if(soundClip != null) { soundClip.start(); } } /** * Stop this track playing. (This method has no effect if the track is not * currently playing.) */ public void stop() { if(soundClip != null) { soundClip.stop(); } } /** * Reset this track to its start. */ public void rewind() { if(soundClip != null) { soundClip.setFramePosition(0); } } /** * Return the name of this track. */ public String getName() { return name; } /** * Return the duration of this track, in seconds. */ public int getDuration() { if (soundClip == null) { return 0; } else { return (int) soundClip.getMicrosecondLength()/1000000; } } /** * Set the playback volume of the current track. * * @param vol Volume level as a percentage (0..100). */ public void setVolume(int vol) { if(soundClip == null) { return; } if(vol &lt; 0 || vol &gt; 100) { vol = 100; } double val = vol / 100.0; try { FloatControl volControl = (FloatControl) soundClip.getControl(FloatControl.Type.MASTER_GAIN); float dB = (float)(Math.log(val == 0.0 ? 0.0001 : val) / Math.log(10.0) * 20.0); volControl.setValue(dB); } catch (Exception ex) { System.err.println("Error: could not set volume"); } } /** * Return true if this track has successfully loaded and can be played. */ public boolean isValid() { return soundClip != null; } /** * Load the sound file supplied by the parameter. * * @return The sound clip if successful, null if the file could not be decoded. */ private Clip loadSound(File file) { Clip newClip; try { AudioInputStream stream = AudioSystem.getAudioInputStream(file); AudioFormat format = stream.getFormat(); // we cannot play ALAW/ULAW, so we convert them to PCM // if ((format.getEncoding() == AudioFormat.Encoding.ULAW) || (format.getEncoding() == AudioFormat.Encoding.ALAW)) { AudioFormat tmp = new AudioFormat( AudioFormat.Encoding.PCM_SIGNED, format.getSampleRate(), format.getSampleSizeInBits() * 2, format.getChannels(), format.getFrameSize() * 2, format.getFrameRate(), true); stream = AudioSystem.getAudioInputStream(tmp, stream); format = tmp; } DataLine.Info info = new DataLine.Info(Clip.class, stream.getFormat(), ((int) stream.getFrameLength() * format.getFrameSize())); newClip = (Clip) AudioSystem.getLine(info); newClip.open(stream); return newClip; } catch (Exception ex) { return null; } } } public class PlayList { private List&lt;Track&gt; tracks; /** * Constructor for objects of class TrackCollection */ public PlayList(String directoryName) { tracks = loadTracks(directoryName); } /** * Return a track from this collection. */ public Track getTrack(int trackNumber) { return tracks.get(trackNumber); } /** * Return the number of tracks in this collection. */ public int numberOfTracks() { return tracks.size(); } /** * Load the file names of all files in the given directory. * @param dirName Directory (folder) name. * @param suffix File suffix of interest. * @return The names of files found. */ private List&lt;Track&gt; loadTracks(String dirName) { File dir = new File(dirName); if(dir.isDirectory()) { File[] allFiles = dir.listFiles(); List&lt;Track&gt; foundTracks = new ArrayList&lt;Track&gt;(); for(File file : allFiles) { //System.out.println("found: " + file); Track track = new Track(file); if(track.isValid()) { foundTracks.add(track); } } return foundTracks; } else { System.err.println("Error: " + dirName + " must be a directory"); return null; } } /** * Return this playlist as an array of strings with the track names. */ public String[] asStrings() { String[] names = new String[tracks.size()]; int i = 0; for(Track track : tracks) { names[i++] = track.getName(); } return names; } } </code></pre> <ol> <li><p>I understand that to call the play methods in the player class, I have to initialize a Track class variable. I also need to initialize it using the PlayList getTrack method. However, how can I initialize it without defining a starting index variable (i.e I don't want it to automatically initialize to a specific song in the index, I want the user to have to select a song first)?</p></li> <li><p>Also, how do I code the play method in the player class to stop a existing song if one is playing before starting a new song and to restart a song if the play method is called again one the same song?</p></li> </ol>
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    1. CO1. http://stackoverflow.com/questions/2707322/what-is-null-in-java 2. Aw, this sounds like "solve my homework assignment for me". You will need more specific questions and more info on what you have tried or what are your reflections so far.
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      1. POA couple of questions about a music project in Java
      1. USKrizz
    2. COI suggest you read the [faq] and [ask] before posting.
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      1. POA couple of questions about a music project in Java
      1. USJim Garrison
 

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