我对Java比较陌生，只是读了一本朋友借给我的书。
问题说
如果您播放两首曲目而不停止第一首曲目，则两首曲目将同时播放。 这不是很有用。更改程序，以便自动播放曲目 启动另一条轨道时停止
这是到目前为止的样子：
public void playTrack(int index)
{
if(indexValid(index)) {
Track track = tracks.get(index);
player.startPlaying(track.getFilename());
track.incrementCount();
System.out.println("Now playing: " + track.getArtist() + " - " +
track.getTitle());
}
我的计划是添加另一个其他 if 语句，然后以某种方式说一首歌曲是否正在播放，然后停止当前并开始下一首，但我不确定该怎么做。
很抱歉，这是我第一次在这个论坛上，我对java很陌生。
下面是使用 API 的此类的完整代码
import java.util.ArrayList;
/**
*/
public class MusicOrganizer
{
// An ArrayList for storing music tracks.
private ArrayList<Track> tracks;
// A player for the music tracks.
private MusicPlayer player;
// A reader that can read music files and load them as tracks.
private TrackReader reader;
/**
* Create a MusicOrganizer
*/
public MusicOrganizer()
{
tracks = new ArrayList<>();
player = new MusicPlayer();
reader = new TrackReader();
readLibrary("../audio");
System.out.println("Music library loaded. " + getNumberOfTracks() + " tracks.");
System.out.println();
}
/**
* Add a track file to the collection.
* @param filename The file name of the track to be added.
*/
public void addFile(String filename)
{
tracks.add(new Track(filename));
}
/**
* Add a track to the collection.
* @param track The track to be added.
*/
public void addTrack(Track track)
{
tracks.add(track);
}
/**
* Play a track in the collection.
* @param index The index of the track to be played.
*/
public void playTrack(int index)
{
if(indexValid(index)) {
Track track = tracks.get(index);
player.startPlaying(track.getFilename());
System.out.println("Now playing: " + track.getArtist() + " - " + track.getTitle());
}
}
/**
* Return the number of tracks in the collection.
* @return The number of tracks in the collection.
*/
public int getNumberOfTracks()
{
return tracks.size();
}
/**
* List a track from the collection.
* @param index The index of the track to be listed.
*/
public void listTrack(int index)
{
System.out.print("Track " + index + ": ");
Track track = tracks.get(index);
System.out.println(track.getDetails());
}
/**
* Show a list of all the tracks in the collection.
*/
public void listAllTracks()
{
System.out.println("Track listing: ");
for(Track track : tracks) {
System.out.println(track.getDetails());
}
System.out.println();
}
/**
* List all tracks by the given artist.
* @param artist The artist's name.
*/
public void listByArtist(String artist)
{
for(Track track : tracks) {
if(track.getArtist().contains(artist)) {
System.out.println(track.getDetails());
}
}
}
/**
* Remove a track from the collection.
* @param index The index of the track to be removed.
*/
public void removeTrack(int index)
{
if(indexValid(index)) {
tracks.remove(index);
}
}
/**
* Play the first track in the collection, if there is one.
*/
public void playFirst()
{
if(tracks.size() > 0) {
player.startPlaying(tracks.get(0).getFilename());
}
}
/**
* Stop the player.
*/
public void stopPlaying()
{
player.stop();
}
/**
* Determine whether the given index is valid for the collection.
* Print an error message if it is not.
* @param index The index to be checked.
* @return true if the index is valid, false otherwise.
*/
private boolean indexValid(int index)
{
// The return value.
// Set according to whether the index is valid or not.
boolean valid;
if(index < 0) {
System.out.println("Index cannot be negative: " + index);
valid = false;
}
else if(index >= tracks.size()) {
System.out.println("Index is too large: " + index);
valid = false;
}
else {
valid = true;
}
return valid;
}
private void readLibrary(String folderName)
{
ArrayList<Track> tempTracks = reader.readTracks(folderName, ".mp3");
// Put all thetracks into the organizer.
for(Track track : tempTracks) {
addTrack(track);
}
在启动index指定的轨道之前，您必须通过执行以下操作来停止所有其他轨道：
for(int i = 0; i < tracks.size(); i++) {
if(i != trackToPlay) {
player.stop(tracks.get(i));
}
}