Merge commit 'b873a17ce7be0a9771c24999adca6964431728f6' into HEAD

Change-Id: I938755073e70602cc8f51ce9bd420fdcf870cecd

1 files changed, 94 insertions, 28 deletions

diff --git a/core/java/android/util/SparseArray.java b/core/java/android/util/SparseArray.java
index 7e8fee56ea95..6e168a8b4ccd 100644
--- a/core/java/android/util/SparseArray.java
+++ b/core/java/android/util/SparseArray.java
@@ -20,8 +20,31 @@ import com.android.internal.util.ArrayUtils;
 
 /**
  * SparseArrays map integers to Objects.  Unlike a normal array of Objects,
- * there can be gaps in the indices.  It is intended to be more efficient
- * than using a HashMap to map Integers to Objects.
+ * there can be gaps in the indices.  It is intended to be more memory efficient
+ * than using a HashMap to map Integers to Objects, both because it avoids
+ * auto-boxing keys 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>
+ *
+ * <p>To help with performance, the container includes an optimization when removing
+ * keys: instead of compacting its array immediately, it leaves the removed entry marked
+ * as deleted.  The entry can then be re-used for the same key, or compacted later in
+ * a single garbage collection step of all removed entries.  This garbage collection will
+ * need to be performed at any time the array needs to be grown or the the map size or
+ * entry values are retrieved.</p>
+ *
+ * <p>It is possible to iterate over the items in this container using
+ * {@link #keyAt(int)} and {@link #valueAt(int)}. Iterating over the keys using
+ * <code>keyAt(int)</code> with ascending values of the index will return the
+ * keys in ascending order, or the values corresponding to the keys in ascending
+ * order in the case of <code>valueAt(int)<code>.</p>
  */
 public class SparseArray<E> implements Cloneable {
     private static final Object DELETED = new Object();
@@ -41,13 +64,19 @@ public class SparseArray<E> implements Cloneable {
     /**
      * Creates a new SparseArray containing no mappings that will not
      * require any additional memory allocation to store the specified
-     * number of mappings.
+     * number of mappings.  If you supply an initial capacity of 0, the
+     * sparse array will be initialized with a light-weight representation
+     * not requiring any additional array allocations.
      */
     public SparseArray(int initialCapacity) {
-        initialCapacity = ArrayUtils.idealIntArraySize(initialCapacity);
-
-        mKeys = new int[initialCapacity];
-        mValues = new Object[initialCapacity];
+        if (initialCapacity == 0) {
+            mKeys = ContainerHelpers.EMPTY_INTS;
+            mValues = ContainerHelpers.EMPTY_OBJECTS;
+        } else {
+            initialCapacity = ArrayUtils.idealIntArraySize(initialCapacity);
+            mKeys = new int[initialCapacity];
+            mValues = new Object[initialCapacity];
+        }
         mSize = 0;
     }
 
@@ -79,7 +108,7 @@ public class SparseArray<E> implements Cloneable {
      */
     @SuppressWarnings("unchecked")
     public E get(int key, E valueIfKeyNotFound) {
-        int i = binarySearch(mKeys, 0, mSize, key);
+        int i = ContainerHelpers.binarySearch(mKeys, mSize, key);
 
         if (i < 0 || mValues[i] == DELETED) {
             return valueIfKeyNotFound;
@@ -92,7 +121,7 @@ public class SparseArray<E> implements Cloneable {
      * Removes the mapping from the specified key, if there was any.
      */
     public void delete(int key) {
-        int i = binarySearch(mKeys, 0, mSize, key);
+        int i = ContainerHelpers.binarySearch(mKeys, mSize, key);
 
         if (i >= 0) {
             if (mValues[i] != DELETED) {
@@ -119,6 +148,19 @@ public class SparseArray<E> implements Cloneable {
         }
     }
 
+    /**
+     * Remove a range of mappings as a batch.
+     *
+     * @param index Index to begin at
+     * @param size Number of mappings to remove
+     */
+    public void removeAtRange(int index, int size) {
+        final int end = Math.min(mSize, index + size);
+        for (int i = index; i < end; i++) {
+            removeAt(i);
+        }
+    }
+
     private void gc() {
         // Log.e("SparseArray", "gc start with " + mSize);
 
@@ -153,7 +195,7 @@ public class SparseArray<E> implements Cloneable {
      * was one.
      */
     public void put(int key, E value) {
-        int i = binarySearch(mKeys, 0, mSize, key);
+        int i = ContainerHelpers.binarySearch(mKeys, mSize, key);
 
         if (i >= 0) {
             mValues[i] = value;
@@ -170,7 +212,7 @@ public class SparseArray<E> implements Cloneable {
                 gc();
 
                 // Search again because indices may have changed.
-                i = ~binarySearch(mKeys, 0, mSize, key);
+                i = ~ContainerHelpers.binarySearch(mKeys, mSize, key);
             }
 
             if (mSize >= mKeys.length) {
@@ -215,6 +257,11 @@ public class SparseArray<E> implements Cloneable {
      * Given an index in the range <code>0...size()-1</code>, returns
      * the key from the <code>index</code>th key-value mapping that this
      * SparseArray stores.
+     *
+     * <p>The keys corresponding to indices in ascending order are guaranteed to
+     * be in ascending order, e.g., <code>keyAt(0)</code> will return the
+     * smallest key and <code>keyAt(size()-1)</code> will return the largest
+     * key.</p>
      */
     public int keyAt(int index) {
         if (mGarbage) {
@@ -228,6 +275,12 @@ public class SparseArray<E> implements Cloneable {
      * Given an index in the range <code>0...size()-1</code>, returns
      * the value from the <code>index</code>th key-value mapping that this
      * SparseArray stores.
+     *
+     * <p>The values corresponding to indices in ascending order are guaranteed
+     * to be associated with keys in ascending order, e.g.,
+     * <code>valueAt(0)</code> will return the value associated with the
+     * smallest key and <code>valueAt(size()-1)</code> will return the value
+     * associated with the largest key.</p>
      */
     @SuppressWarnings("unchecked")
     public E valueAt(int index) {
@@ -261,7 +314,7 @@ public class SparseArray<E> implements Cloneable {
             gc();
         }
 
-        return binarySearch(mKeys, 0, mSize, key);
+        return ContainerHelpers.binarySearch(mKeys, mSize, key);
     }
 
     /**
@@ -335,23 +388,36 @@ public class SparseArray<E> implements Cloneable {
         mSize = pos + 1;
     }
 
-    private static int binarySearch(int[] a, int start, int len, int key) {
-        int high = start + len, low = start - 1, guess;
-
-        while (high - low > 1) {
-            guess = (high + low) / 2;
-
-            if (a[guess] < key)
-                low = guess;
-            else
-                high = guess;
+    /**
+     * {@inheritDoc}
+     *
+     * <p>This implementation composes a string by iterating over its mappings. If
+     * this map contains itself as a value, the string "(this Map)"
+     * will appear in its place.
+     */
+    @Override
+    public String toString() {
+        if (size() <= 0) {
+            return "{}";
         }
 
-        if (high == start + len)
-            return ~(start + len);
-        else if (a[high] == key)
-            return high;
-        else
-            return ~high;
+        StringBuilder buffer = new StringBuilder(mSize * 28);
+        buffer.append('{');
+        for (int i=0; i<mSize; i++) {
+            if (i > 0) {
+                buffer.append(", ");
+            }
+            int key = keyAt(i);
+            buffer.append(key);
+            buffer.append('=');
+            Object value = valueAt(i);
+            if (value != this) {
+                buffer.append(value);
+            } else {
+                buffer.append("(this Map)");
+            }
+        }
+        buffer.append('}');
+        return buffer.toString();
     }
 }