Add documentation to CollectionUtils methods

pgpainless-core/src/main/java/org/pgpainless/util/CollectionUtils.java

@@ -15,6 +15,13 @@ public final class CollectionUtils {
 
     }
 
+    /**
+     * Return all items returned by the {@link Iterator} as a {@link List}.
+     *
+     * @param iterator iterator
+     * @param <I> type
+     * @return list
+     */
     public static <I> List<I> iteratorToList(Iterator<I> iterator) {
         List<I> items = new ArrayList<>();
         while (iterator.hasNext()) {
@@ -24,6 +31,13 @@ public final class CollectionUtils {
         return items;
     }
 
+    /**
+     * Return a new array which contains <pre>t</pre> as first element, followed by the elements of <pre>ts</pre>.
+     * @param t head
+     * @param ts tail
+     * @param <T> type
+     * @return t and ts as array
+     */
     public static <T> T[] concat(T t, T[] ts) {
         T[] concat = (T[]) Array.newInstance(t.getClass(), ts.length + 1);
         concat[0] = t;
@@ -31,6 +45,13 @@ public final class CollectionUtils {
         return concat;
     }
 
+    /**
+     * Return true, if the given array <pre>ts</pre> contains the element <pre>t</pre>.
+     * @param ts elements
+     * @param t searched element
+     * @param <T> type
+     * @return true if ts contains t, false otherwise
+     */
     public static <T> boolean contains(T[] ts, T t) {
         for (T i : ts) {
             if (i.equals(t)) {