1 files changed, 12 insertions, 1 deletions

diff --git a/java/src/com/android/inputmethod/latin/utils/CollectionUtils.java b/java/src/com/android/inputmethod/latin/utils/CollectionUtils.java
index f9839eb91..01f5e1079 100644
--- a/java/src/com/android/inputmethod/latin/utils/CollectionUtils.java
+++ b/java/src/com/android/inputmethod/latin/utils/CollectionUtils.java
@@ -22,16 +22,27 @@ import java.util.Collection;
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
+/**
+ * Utility methods for working with collections.
+ */
 public final class CollectionUtils {
     private CollectionUtils() {
         // This utility class is not publicly instantiable.
     }
 
+    /**
+     * Converts a sub-range of the given array to an ArrayList of the appropriate type.
+     * @param array Array to be converted.
+     * @param start First index inclusive to be converted.
+     * @param end Last index exclusive to be converted.
+     * @throws IllegalArgumentException if start or end are out of range or start > end.
+     */
     @Nonnull
     public static <E> ArrayList<E> arrayAsList(@Nonnull final E[] array, final int start,
             final int end) {
         if (start < 0 || start > end || end > array.length) {
-            throw new IllegalArgumentException();
+            throw new IllegalArgumentException("Invalid start: " + start + " end: " + end
+                    + " with array.length: " + array.length);
         }
 
         final ArrayList<E> list = new ArrayList<>(end - start);