Update SparseArray docs to be more informative.

Change-Id: I5d8d17d46a69ccdcf6b29f93be3d44addd80ab61

1 files changed, 12 insertions, 2 deletions

diff --git a/core/java/android/util/LongSparseLongArray.java b/core/java/android/util/LongSparseLongArray.java
index 503295c..d795308 100644
--- a/core/java/android/util/LongSparseLongArray.java
+++ b/core/java/android/util/LongSparseLongArray.java
@@ -22,8 +22,18 @@ import java.util.Arrays;
 
 /**
  * Map of {@code long} to {@code long}. Unlike a normal array of longs, there
- * can be gaps in the indices. It is intended to be more efficient than using a
- * {@code HashMap}.
+ * can be gaps in the indices. It is intended to be more memory efficient than using a
+ * {@code HashMap}, both because it avoids
+ * auto-boxing keys and values and its data structure doesn't rely on an extra entry object
+ * for each mapping.
+ *
+ * <p>Note that this container keeps its mappings in an array data structure,
+ * using a binary search to find keys.  The implementation is not intended to be appropriate for
+ * data structures
+ * that may contain large numbers of items.  It is generally slower than a traditional
+ * HashMap, since lookups require a binary search and adds and removes require inserting
+ * and deleting entries in the array.  For containers holding up to hundreds of items,
+ * the performance difference is not significant, less than 50%.</p>
  *
  * @hide
  */