Android 移动端数据结构

## SparseArray

## SparseBooleanArray

## SparseIntArray

## SparseLongArray

* 位于android.util，Android 中的数据结构，针对移动端做了优化，在数据量比较少的情况下，性能会好过 HashMap，类似于 HashMap，key:int ,value:object 。

* 为什么性能会好：

1. key  和 value  采用数组进行存储。存储 key 的数组是 int 类型，不需要进行装箱操作。提供了速度。

2. 采用二分查找法，在插入进行了排序，所以两个数组是按照从小到大进行排序的。

3. 在查找的时候，进行二分查找，数据量少的情况下，速度比较快。

同时还有一个类：SparseArrayCompat，位于android.support.v4.util，与 SparseArray 一样的。

其中有好几个类似的数据结构：SparseBooleanArray（key:int, value:boolean）, SparseIntArray(key:int, value:int), SparseLongArray(key:int, value:long). SparseArray 通过数组对 key , value 进行存储。

在 map Integers to Objects 方面进行了优化，所以比使用 HashMap 提高了性能，建议遇到key:int, value:object 的情况下使用。

构造方法：

默认构造方法中会创建长度为 10 的数组来分别储存 key 和 value。

可以自己在手动输入一个数字，来创建一个指定长度的数组来存储key 和 value。

增：

public void put(int key, E value)  // 存储指定key 和指定value ，假如指定key 已经有了在映射中，替换掉已经存在的。
public void append(int key, E value) // 储存 key value 到数组，key 的索引应该大于数组中的已有索引

删：

public void delete(int key)  // 删除指定key
public void remove(int key)  // 调用 delete 方法
public void removeAt(int index) // 删除指定索引
public void removeAtRange(int index, int size) //删除指定范围的索引
public void clear()  //清空所有内容

改：

public void put(int key, E value)  // 指定key 已存在的情况下，更新，不存在的情况下，增加
public void setValueAt(int index, E value) // 更新指定索引的 value

查：

public E get(int key)   // 得到指定key 的 value,调用的是 get(int key, null)
public E get(int key, E valueIfKeyNotFound) // 返回指定key 的value,没有的情况下，返回传入的默认值
public int indexOfKey(int key) // 传入key 的索引
public int indexOfValue(E value) // 传入 value 的索引
public int keyAt(int index) // 指定索引的 key
public E valueAt(int index) //指定索引的 value

源码：

 public class SparseArray<E> implements Cloneable {
     private static final Object DELETED = new Object();
     private boolean mGarbage = false;

     private int[] mKeys;
     private Object[] mValues;
     private int mSize;

     /**
      * Creates a new SparseArray containing no mappings.
      */
     public SparseArray() {
         this(10);
     }

     /**
      * 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.
      */
     public SparseArray(int initialCapacity) {
         if (initialCapacity == 0) {
             mKeys = EmptyArray.INT;
             mValues = EmptyArray.OBJECT;
         } else {
             mValues = ArrayUtils.newUnpaddedObjectArray(initialCapacity);
             mKeys = new int[mValues.length];
         }
         mSize = 0;
     }

     @Override
     @SuppressWarnings("unchecked")
     public SparseArray<E> clone() {
         SparseArray<E> clone = null;
         try {
             clone = (SparseArray<E>) super.clone();
             clone.mKeys = mKeys.clone();
             clone.mValues = mValues.clone();
         } catch (CloneNotSupportedException cnse) {
             /* ignore */
         }
         return clone;
     }

     /**
      * Gets the Object mapped from the specified key, or <code>null</code>
      * if no such mapping has been made.
      */
     public E get(int key) {
         return get(key, null);
     }

     /**
      * Gets the Object mapped from the specified key, or the specified Object
      * if no such mapping has been made.
      */
     @SuppressWarnings("unchecked")
     public E get(int key, E valueIfKeyNotFound) {
         int i = ContainerHelpers.binarySearch(mKeys, mSize, key);

         if (i < 0 || mValues[i] == DELETED) {
             return valueIfKeyNotFound;
         } else {
             return (E) mValues[i];
         }
     }

     /**
      * Removes the mapping from the specified key, if there was any.
      */
     public void delete(int key) {
         int i = ContainerHelpers.binarySearch(mKeys, mSize, key);

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

     /**
      * @hide
      * Removes the mapping from the specified key, if there was any, returning the old value.
      */
     public E removeReturnOld(int key) {
         int i = ContainerHelpers.binarySearch(mKeys, mSize, key);

         if (i >= 0) {
             if (mValues[i] != DELETED) {
                 final E old = (E) mValues[i];
                 mValues[i] = DELETED;
                 mGarbage = true;
                 return old;
             }
         }
         return null;
     }

     /**
      * Alias for {@link #delete(int)}.
      */
     public void remove(int key) {
         delete(key);
     }

     /**
      * Removes the mapping at the specified index.
      */
     public void removeAt(int index) {
         if (mValues[index] != DELETED) {
             mValues[index] = DELETED;
             mGarbage = true;
         }
     }

     /**
      * 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);

         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);
     }

     /**
      * Adds a mapping from the specified key to the specified value,
      * replacing the previous mapping from the specified key if there
      * was one.
      */
     public void put(int key, E value) {
         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++;
         }
     }

     /**
      * Returns the number of key-value mappings that this SparseArray
      * currently stores.
      */
     public int size() {
         if (mGarbage) {
             gc();
         }

         return mSize;
     }

     /**
      * 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) {
             gc();
         }

         return mKeys[index];
     }

     /**
      * 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) {
         if (mGarbage) {
             gc();
         }

         return (E) mValues[index];
     }

     /**
      * Given an index in the range <code>0...size()-1</code>, sets a new
      * value for the <code>index</code>th key-value mapping that this
      * SparseArray stores.
      */
     public void setValueAt(int index, E value) {
         if (mGarbage) {
             gc();
         }

         mValues[index] = value;
     }

     /**
      * Returns the index for which {@link #keyAt} would return the
      * specified key, or a negative number if the specified
      * key is not mapped.
      */
     public int indexOfKey(int key) {
         if (mGarbage) {
             gc();
         }

         return ContainerHelpers.binarySearch(mKeys, mSize, key);
     }

     /**
      * Returns an index for which {@link #valueAt} would return the
      * specified key, or a negative number if no keys map to the
      * specified value.
      * <p>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.
      * <p>Note also that unlike most collections' {@code indexOf} methods,
      * this method compares values using {@code ==} rather than {@code equals}.
      */
     public int indexOfValue(E value) {
         if (mGarbage) {
             gc();
         }

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

         return -1;
     }

     /**
      * Removes all key-value mappings from this SparseArray.
      */
     public void clear() {
         int n = mSize;
         Object[] values = mValues;

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

         mSize = 0;
         mGarbage = false;
     }

     /**
      * Puts a key/value pair into the array, optimizing for the case where
      * the key is greater than all existing keys in the array.
      */
     public void append(int key, E value) {
         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++;
     }

     /**
      * {@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 "{}";
         }

         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();
     }
 }

##  ArrayMap

* 与 SparseArray 类似