Improved shuffle

src/main/java/tech/sbdevelopment/themeparkaudio/api/maps/SongList.java

@@ -1,7 +1,7 @@
 package tech.sbdevelopment.themeparkaudio.api.maps;
 
 import java.util.ArrayList;
-import java.util.Random;
+import java.util.concurrent.ThreadLocalRandom;
 
 /**
  * An {@link ArrayList} with shuffle support.
@@ -9,15 +9,14 @@ import java.util.Random;
  * @param <E> The type you want to store
  */
 public class SongList<E> extends ArrayList<E> {
-    private final Random r = new Random();
-
     /**
-     * Shuffle this List
+     * Shuffle this List using the Fisher-Yates algorithm
      */
     public void shuffle() {
-        for (int index = 0; index < size(); index++) {
-            int secondIndex = r.nextInt(size());
-            swap(index, secondIndex);
+        ThreadLocalRandom rnd = ThreadLocalRandom.current();
+        for (int i = size() - 1; i > 0; i--) {
+            int index = rnd.nextInt(i + 1);
+            swap(index, i);
         }
     }
 
@@ -29,7 +28,7 @@ public class SongList<E> extends ArrayList<E> {
     public E getRandom() {
         int size = size();
         if (size == 0) return null;
-        return get(r.nextInt(size()));
+        return get(ThreadLocalRandom.current().nextInt(size));
     }
 
     /**
@@ -39,10 +38,8 @@ public class SongList<E> extends ArrayList<E> {
      * @param secondIndex The second index
      */
     private void swap(int firstIndex, int secondIndex) {
-        E first = get(firstIndex);
-        E second = get(secondIndex);
-
-        set(secondIndex, first);
-        set(firstIndex, second);
+        E temp = get(firstIndex);
+        set(firstIndex, get(secondIndex));
+        set(secondIndex, temp);
     }
 }