Merge "Support varargs for concatElements"

2 files changed, 88 insertions, 12 deletions

diff --git a/core/java/com/android/internal/util/ArrayUtils.java b/core/java/com/android/internal/util/ArrayUtils.java
index b73ecd1974aa..e3264a054a43 100644
--- a/core/java/com/android/internal/util/ArrayUtils.java
+++ b/core/java/com/android/internal/util/ArrayUtils.java
@@ -320,23 +320,63 @@ public class ArrayUtils {
         return array;
     }
 
+    /**
+     * Combine multiple arrays into a single array.
+     *
+     * @param kind The class of the array elements
+     * @param arrays The arrays to combine
+     * @param <T> The class of the array elements (inferred from kind).
+     * @return A single array containing all the elements of the parameter arrays.
+     */
     @SuppressWarnings("unchecked")
-    public static @NonNull <T> T[] concatElements(Class<T> kind, @Nullable T[] a, @Nullable T[] b) {
-        final int an = (a != null) ? a.length : 0;
-        final int bn = (b != null) ? b.length : 0;
-        if (an == 0 && bn == 0) {
-            if (kind == String.class) {
-                return (T[]) EmptyArray.STRING;
-            } else if (kind == Object.class) {
-                return (T[]) EmptyArray.OBJECT;
+    public static @NonNull <T> T[] concatElements(Class<T> kind, @Nullable T[]... arrays) {
+        if (arrays == null || arrays.length == 0) {
+            return createEmptyArray(kind);
+        }
+
+        int totalLength = 0;
+        int maxLength = 0;
+        T[] maxLengthArray = arrays[0];
+        for (T[] item : arrays) {
+            if (item == null) {
+                continue;
+            }
+
+            totalLength += item.length;
+            if (item.length > maxLength) {
+                maxLengthArray = item;
+                maxLength = item.length;
+            }
+        }
+
+        // Optimization for entirely empty arrays.
+        if (totalLength == 0) {
+            return createEmptyArray(kind);
+        }
+
+        final T[] all = (T[]) Array.newInstance(kind, totalLength);
+        int pos = 0;
+        for (T[] item : arrays) {
+            if (item == null || item.length == 0) {
+                continue;
             }
+            System.arraycopy(item, 0, all, pos, item.length);
+            pos += item.length;
         }
-        final T[] res = (T[]) Array.newInstance(kind, an + bn);
-        if (an > 0) System.arraycopy(a, 0, res, 0, an);
-        if (bn > 0) System.arraycopy(b, 0, res, an, bn);
-        return res;
+        return all;
     }
 
+    private static @NonNull <T> T[] createEmptyArray(Class<T> kind) {
+        if (kind == String.class) {
+            return (T[]) EmptyArray.STRING;
+        } else if (kind == Object.class) {
+            return (T[]) EmptyArray.OBJECT;
+        }
+
+        return (T[]) Array.newInstance(kind, 0);
+    }
+
+
     /**
      * Adds value to given array if not already present, providing set-like
      * behavior.
diff --git a/core/tests/utiltests/src/com/android/internal/util/ArrayUtilsTest.java b/core/tests/utiltests/src/com/android/internal/util/ArrayUtilsTest.java
index 39bb84a20d7a..cb30b3fe5b82 100644
--- a/core/tests/utiltests/src/com/android/internal/util/ArrayUtilsTest.java
+++ b/core/tests/utiltests/src/com/android/internal/util/ArrayUtilsTest.java
@@ -177,4 +177,40 @@ public class ArrayUtilsTest extends TestCase {
         assertArrayEquals(new Long[] { 1L, 2L, 3L, 4L },
                 concatElements(Long.class, new Long[] { 1L, 2L }, new Long[] { 3L, 4L }));
     }
+
+    public void testConcatElements_threeWay() {
+        String[] array1 = { "1", "2" };
+        String[] array2 = { "3", "4" };
+        String[] array3 = { "5", "6" };
+        String[] expectation = {"1", "2", "3", "4", "5", "6"};
+
+        String[] concatResult = ArrayUtils.concatElements(String.class, array1, array2, array3);
+        assertArrayEquals(expectation, concatResult);
+    }
+
+
+    public void testConcatElements_threeWayWithNull() {
+        String[] array1 = { "1", "2" };
+        String[] array2 = null;
+        String[] array3 = { "5", "6" };
+        String[] expectation = {"1", "2", "5", "6"};
+
+        String[] concatResult = ArrayUtils.concatElements(String.class, array1, array2, array3);
+        assertArrayEquals(expectation, concatResult);
+    }
+
+    public void testConcatElements_zeroElements() {
+        String[] expectation = new String[0];
+
+        String[] concatResult = ArrayUtils.concatElements(String.class);
+        assertArrayEquals(expectation, concatResult);
+    }
+
+    public void testConcatElements_oneNullElement() {
+        String[] expectation = new String[0];
+
+        String[] concatResult = ArrayUtils.concatElements(String.class, null);
+        assertArrayEquals(expectation, concatResult);
+    }
+
 }