Decoupled Player and PlayerGUI, dependency between the two is now injected instead.

pom.xml

@@ -97,6 +97,11 @@
             <version>2.0.2</version>
             <scope>compile</scope>
         </dependency>
+        <dependency>
+            <groupId>com.google.inject</groupId>
+            <artifactId>guice</artifactId>
+            <version>4.0</version>
+        </dependency>
     </dependencies>
 
     <repositories>

src/main/java/musicplayer/BindingsModule.java

@@ -0,0 +1,14 @@
+package musicplayer;
+
+import com.google.inject.AbstractModule;
+import musicplayer.callbacks.PlayerCallbackInterface;
+import musicplayer.player.IPlayer;
+import musicplayer.player.GStreamerPlayer;
+
+public class BindingsModule extends AbstractModule {
+    @Override
+    protected void configure() {
+        bind(IPlayer.class).to(GStreamerPlayer.class);
+        bind(PlayerCallbackInterface.class).to(PlayerGUI.class);
+    }
+}

src/main/java/musicplayer/PlayerGUI.java

@@ -1,5 +1,8 @@
 package musicplayer;
 
+import com.google.inject.Guice;
+import com.google.inject.Inject;
+import com.google.inject.Injector;
 import musicplayer.callbacks.LibraryCallbackInterface;
 import musicplayer.callbacks.PlayerCallbackInterface;
 import musicplayer.db.DatabaseManager;
@@ -8,6 +11,7 @@ import musicplayer.model.Album;
 import musicplayer.model.Artist;
 import musicplayer.model.HasSongs;
 import musicplayer.model.Song;
+import musicplayer.player.IPlayer;
 import musicplayer.swingmodels.PlaylistTableModel;
 import musicplayer.util.Icons;
 import musicplayer.util.LibraryUtils;
@@ -47,7 +51,7 @@ public class PlayerGUI implements PlayerCallbackInterface, LibraryCallbackInterf
     private final JTable playList = new JTable();
     private JSlider seekBar;
     private final JComboBox<String> libraryDisplayType = new JComboBox<>();
-    private final Player player = new Player(this);
+    private final IPlayer player;
     private final PlaylistTableModel playlistTableModel = new PlaylistTableModel(new ArrayList<>());
     private static final DefaultMutableTreeNode updatingNode = new DefaultMutableTreeNode();
     private boolean libraryUpdating = false;
@@ -55,7 +59,9 @@ public class PlayerGUI implements PlayerCallbackInterface, LibraryCallbackInterf
 
     private final Map<String, Runnable> libraryDisplayVariants = createDisplayVariantMap();
 
-    public PlayerGUI() {
+    @Inject
+    public PlayerGUI(IPlayer player) {
+        this.player = player;
         createUI();
         resetTree();
         Thread seekBarUpdater = new Thread(() -> {
@@ -97,7 +103,8 @@ public class PlayerGUI implements PlayerCallbackInterface, LibraryCallbackInterf
 
     public static void main(String[] args) {
         DatabaseManager.init();
-        PlayerGUI playerGUI = new PlayerGUI();
+        Injector injector = Guice.createInjector(new BindingsModule());
+        PlayerGUI playerGUI = injector.getInstance(PlayerGUI.class);
         JFrame frame = new JFrame();
         frame.setMinimumSize(new Dimension(600, 400));
         frame.setContentPane(playerGUI.mainPanel);

src/main/java/musicplayer/player/GStreamerPlayer.java

@@ -1,5 +1,7 @@
-package musicplayer;
+package musicplayer.player;
 
+import com.google.inject.Inject;
+import musicplayer.StartPlayingException;
 import musicplayer.callbacks.PlayerCallbackInterface;
 import musicplayer.model.Song;
 import org.gstreamer.ClockTime;
@@ -11,7 +13,7 @@ import org.gstreamer.elements.PlayBin2;
 import java.io.File;
 import java.util.Optional;
 
-class Player {
+public class GStreamerPlayer implements IPlayer{
 
     private final PlayBin2 playBin;
 
@@ -25,7 +27,8 @@ class Player {
      * Manages GStreamer based playback operations.
      * @param callbackInterface Interface on which UI updates can be called.
      */
-    public Player(PlayerCallbackInterface callbackInterface) {
+    @Inject
+    public GStreamerPlayer(PlayerCallbackInterface callbackInterface) {
         this.callbackInterface = callbackInterface;
         Gst.init();
         playBin = new PlayBin2("BusMessages");

src/main/java/musicplayer/player/IPlayer.java

@@ -0,0 +1,19 @@
+package musicplayer.player;
+
+import musicplayer.StartPlayingException;
+import musicplayer.model.Song;
+
+import java.util.Optional;
+
+public interface IPlayer {
+    void playSong(Optional<Song> inputSong) throws StartPlayingException;
+    void stop();
+    void resume();
+    void pause();
+    Song getCurrentSong();
+    int currentSongPosition();
+    void setVolume(int volume);
+    int getVolume();
+    void seek(int position);
+    boolean isPlaying();
+}