Prefer ArrayDeque over ArrayList

You should consider using ArrayDeque when:

You need a collection that efficiently supports adding and removing elements from both ends. This makes it ideal for implementing data structures like queues and stacks.
You frequently perform removals from the beginning of the collection.
see ALAudioRenderer.newChannel() and ALAudioRenderer.freeChannel()

jme3-core/src/main/java/com/jme3/audio/openal/ALAudioRenderer.java

@@ -51,6 +51,7 @@ import com.jme3.util.NativeObjectManager;
 import java.nio.ByteBuffer;
 import java.nio.FloatBuffer;
 import java.nio.IntBuffer;
+import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.logging.Level;
 import java.util.logging.Logger;
@@ -81,7 +82,7 @@ public class ALAudioRenderer implements AudioRenderer, Runnable {
     private int[] channels; // OpenAL source IDs
     private AudioSource[] channelSources; // jME source associated with each channel
     private int nextChannelIndex = 0; // Next available channel index
-    private final ArrayList<Integer> freeChannels = new ArrayList<>(); // Pool of freed channels
+    private final ArrayDeque<Integer> freeChannels = new ArrayDeque<>(); // Pool of freed channels
 
     // Listener and environment
     private Listener listener;
@@ -793,7 +794,7 @@ public class ALAudioRenderer implements AudioRenderer, Runnable {
 
     private int newChannel() {
         if (!freeChannels.isEmpty()) {
-            return freeChannels.remove(0);
+            return freeChannels.removeFirst();
         } else if (nextChannelIndex < channels.length) {
             return nextChannelIndex++;
         } else {
@@ -906,7 +907,7 @@ public class ALAudioRenderer implements AudioRenderer, Runnable {
         for (int i = 0; i < processed; i++) {
             int buffer;
 
-            ib.position(0).limit(1);
+            ib.clear().limit(1);
             al.alSourceUnqueueBuffers(sourceId, 1, ib);
             buffer = ib.get(0);
 
@@ -931,7 +932,7 @@ public class ALAudioRenderer implements AudioRenderer, Runnable {
             }
 
             if (filled) {
-                ib.position(0).limit(1);
+                ib.clear().limit(1);
                 ib.put(0, buffer);
                 al.alSourceQueueBuffers(sourceId, 1, ib);
                 // At least one buffer enqueued = success.
@@ -974,7 +975,7 @@ public class ALAudioRenderer implements AudioRenderer, Runnable {
             }
 
             if (filled) {
-                ib.position(0).limit(1);
+                ib.clear().limit(1);
                 ib.put(id).flip();
                 al.alSourceQueueBuffers(sourceId, 1, ib);
                 success = true;