FileDocCategorySizeDatePackage
SparseArray.javaAPI DocAndroid 5.1 API11753Thu Mar 12 22:22:10 GMT 2015android.util

SparseArray

public class SparseArray extends Object implements Cloneable
SparseArrays map integers to Objects. Unlike a normal array of 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.

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%.

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.

It is possible to iterate over the items in this container using {@link #keyAt(int)} and {@link #valueAt(int)}. Iterating over the keys using keyAt(int) 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 valueAt(int).

Fields Summary
private static final Object
DELETED
private boolean
mGarbage
private int[]
mKeys
private Object[]
mValues
private int
mSize
Constructors Summary
public SparseArray()
Creates a new SparseArray containing no mappings.


                
      
        this(10);
public SparseArray(int initialCapacity)
Creates a new SparseArray containing no mappings that will not require any additional memory allocation to store the specified 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.

        if (initialCapacity == 0) {
            mKeys = EmptyArray.INT;
            mValues = EmptyArray.OBJECT;
        } else {
            mValues = ArrayUtils.newUnpaddedObjectArray(initialCapacity);
            mKeys = new int[mValues.length];
        }
        mSize = 0;
Methods Summary
public voidappend(int key, E value)
Puts a key/value pair into the array, optimizing for the case where the key is greater than all existing keys in the array.

        if (mSize != 0 && key <= mKeys[mSize - 1]) {
            put(key, value);
            return;
        }

        if (mGarbage && mSize >= mKeys.length) {
            gc();
        }

        mKeys = GrowingArrayUtils.append(mKeys, mSize, key);
        mValues = GrowingArrayUtils.append(mValues, mSize, value);
        mSize++;
public voidclear()
Removes all key-value mappings from this SparseArray.

        int n = mSize;
        Object[] values = mValues;

        for (int i = 0; i < n; i++) {
            values[i] = null;
        }

        mSize = 0;
        mGarbage = false;
public android.util.SparseArrayclone()

        SparseArray<E> clone = null;
        try {
            clone = (SparseArray<E>) super.clone();
            clone.mKeys = mKeys.clone();
            clone.mValues = mValues.clone();
        } catch (CloneNotSupportedException cnse) {
            /* ignore */
        }
        return clone;
public voiddelete(int key)
Removes the mapping from the specified key, if there was any.

        int i = ContainerHelpers.binarySearch(mKeys, mSize, key);

        if (i >= 0) {
            if (mValues[i] != DELETED) {
                mValues[i] = DELETED;
                mGarbage = true;
            }
        }
private voidgc()

        // Log.e("SparseArray", "gc start with " + mSize);

        int n = mSize;
        int o = 0;
        int[] keys = mKeys;
        Object[] values = mValues;

        for (int i = 0; i < n; i++) {
            Object val = values[i];

            if (val != DELETED) {
                if (i != o) {
                    keys[o] = keys[i];
                    values[o] = val;
                    values[i] = null;
                }

                o++;
            }
        }

        mGarbage = false;
        mSize = o;

        // Log.e("SparseArray", "gc end with " + mSize);
public Eget(int key)
Gets the Object mapped from the specified key, or null if no such mapping has been made.

        return get(key, null);
public Eget(int key, E valueIfKeyNotFound)
Gets the Object mapped from the specified key, or the specified Object if no such mapping has been made.

        int i = ContainerHelpers.binarySearch(mKeys, mSize, key);

        if (i < 0 || mValues[i] == DELETED) {
            return valueIfKeyNotFound;
        } else {
            return (E) mValues[i];
        }
public intindexOfKey(int key)
Returns the index for which {@link #keyAt} would return the specified key, or a negative number if the specified key is not mapped.

        if (mGarbage) {
            gc();
        }

        return ContainerHelpers.binarySearch(mKeys, mSize, key);
public intindexOfValue(E value)
Returns an index for which {@link #valueAt} would return the specified key, or a negative number if no keys map to the specified value.

Beware that this is a linear search, unlike lookups by key, and that multiple keys can map to the same value and this will find only one of them.

Note also that unlike most collections' {@code indexOf} methods, this method compares values using {@code ==} rather than {@code equals}.

        if (mGarbage) {
            gc();
        }

        for (int i = 0; i < mSize; i++)
            if (mValues[i] == value)
                return i;

        return -1;
public intkeyAt(int index)
Given an index in the range 0...size()-1, returns the key from the indexth key-value mapping that this SparseArray stores.

The keys corresponding to indices in ascending order are guaranteed to be in ascending order, e.g., keyAt(0) will return the smallest key and keyAt(size()-1) will return the largest key.

        if (mGarbage) {
            gc();
        }

        return mKeys[index];
public voidput(int key, E value)
Adds a mapping from the specified key to the specified value, replacing the previous mapping from the specified key if there was one.

        int i = ContainerHelpers.binarySearch(mKeys, mSize, key);

        if (i >= 0) {
            mValues[i] = value;
        } else {
            i = ~i;

            if (i < mSize && mValues[i] == DELETED) {
                mKeys[i] = key;
                mValues[i] = value;
                return;
            }

            if (mGarbage && mSize >= mKeys.length) {
                gc();

                // Search again because indices may have changed.
                i = ~ContainerHelpers.binarySearch(mKeys, mSize, key);
            }

            mKeys = GrowingArrayUtils.insert(mKeys, mSize, i, key);
            mValues = GrowingArrayUtils.insert(mValues, mSize, i, value);
            mSize++;
        }
public voidremove(int key)
Alias for {@link #delete(int)}.

        delete(key);
public voidremoveAt(int index)
Removes the mapping at the specified index.

        if (mValues[index] != DELETED) {
            mValues[index] = DELETED;
            mGarbage = true;
        }
public voidremoveAtRange(int index, int size)
Remove a range of mappings as a batch.

param
index Index to begin at
param
size Number of mappings to remove

        final int end = Math.min(mSize, index + size);
        for (int i = index; i < end; i++) {
            removeAt(i);
        }
public voidsetValueAt(int index, E value)
Given an index in the range 0...size()-1, sets a new value for the indexth key-value mapping that this SparseArray stores.

        if (mGarbage) {
            gc();
        }

        mValues[index] = value;
public intsize()
Returns the number of key-value mappings that this SparseArray currently stores.

        if (mGarbage) {
            gc();
        }

        return mSize;
public java.lang.StringtoString()
{@inheritDoc}

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.

        if (size() <= 0) {
            return "{}";
        }

        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();
public EvalueAt(int index)
Given an index in the range 0...size()-1, returns the value from the indexth key-value mapping that this SparseArray stores.

The values corresponding to indices in ascending order are guaranteed to be associated with keys in ascending order, e.g., valueAt(0) will return the value associated with the smallest key and valueAt(size()-1) will return the value associated with the largest key.

        if (mGarbage) {
            gc();
        }

        return (E) mValues[index];