Emulate Collections.shuffle
Change-Id: I39f041d4fe79d658ff9401adb0269a508e8eded7
diff --git a/user/super/com/google/gwt/emul/java/util/Collections.java b/user/super/com/google/gwt/emul/java/util/Collections.java
index ea8587c..4347f66 100644
--- a/user/super/com/google/gwt/emul/java/util/Collections.java
+++ b/user/super/com/google/gwt/emul/java/util/Collections.java
@@ -849,6 +849,10 @@
}
}
+ private static class RandomHolder {
+ private static final Random rnd = new Random();
+ }
+
@SuppressWarnings("unchecked")
public static final List EMPTY_LIST = new EmptyList();
@@ -1228,6 +1232,30 @@
}
}
+ public static <T> void shuffle(List<T> list) {
+ shuffle(list, RandomHolder.rnd);
+ }
+
+ @SuppressWarnings("unchecked")
+ public static <T> void shuffle(List<T> list, Random rnd) {
+ if (list instanceof RandomAccess) {
+ for (int i = list.size() - 1; i >= 1; i--) {
+ swapImpl(list, i, rnd.nextInt(i + 1));
+ }
+ } else {
+ Object arr[] = list.toArray();
+ for (int i = arr.length - 1; i >= 1; i--) {
+ swapImpl(arr, i, rnd.nextInt(i + 1));
+ }
+
+ ListIterator<T> it = list.listIterator();
+ for (Object e : arr) {
+ it.next();
+ it.set((T) e);
+ }
+ }
+ }
+
public static <T> Set<T> singleton(T o) {
HashSet<T> set = new HashSet<T>(1);
set.add(o);
@@ -1337,4 +1365,10 @@
list.set(i, list.get(j));
list.set(j, t);
}
+
+ private static void swapImpl(Object[] a, int i, int j) {
+ Object obj = a[i];
+ a[i] = a[j];
+ a[j] = obj;
+ }
}
