java.lang.Object
net.i2p.router.crypto.ratchet.SparseArray<E>
Type Parameters:
E - type of objects stored in this sparse array
All Implemented Interfaces:
Cloneable
class SparseArray<E>extends Object implements Cloneable
Memory-efficient sparse array implementation for integer-to-object mappings using binary search lookup, optimized for collections with up to hundreds of items

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 HashMap because lookups require a binary search, and adds and removes require inserting and deleting entries in array. For containers holding up to hundreds of items, the performance difference is 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 of all removed entries. This garbage collection must be performed whenever the array needs to be grown, or when the map size or entry values are retrieved.

It is possible to iterate over the items in this container using keyAt(int) and valueAt(int). Iterating over keys using keyAt(int) with ascending values of index returns keys in ascending order. In the case of valueAt(int), values corresponding to keys are returned in ascending order.

I2P - as of 0.9.48, changed to use chars for the index, max value 65535.

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private static final Object
    DELETED
    The marker of a deleted value.
    private static final char[]
    EMPTY_CHARS
    The empty key array.
    private static final Object[]
    EMPTY_OBJECTS
    The empty value array.
    private boolean
    mGarbage
    True when deleted entries await collection.
    private char[]
    mKeys
    The array of keys.
    private int
    mSize
    The number of entries.
    private Object[]
    mValues
    The array of values.

  • Constructor Summary

    Modifier
    Constructor
    Description
    SparseArray()
    Creates a new SparseArray containing no mappings.
    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.
    private
    SparseArray(SparseArray<E> source)
    Copy constructor.

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    append(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.
    void
    clear()
    Removes all key-value mappings from this SparseArray.
    SparseArray<E>
    clone()
    Returns a shallow copy of this SparseArray with deep-copied key and value arrays so the clone's internal arrays are independent of the original's.
    void
    delete(int key)
    Removes the mapping from the specified key, if there was any.
    private void
    gc()
    Removes the deleted entries.
    E
    get(int key)
    Object mapped from the specified key, or null if no such mapping has been made.
    E
    get(int key, E valueIfKeyNotFound)
    Object mapped from the specified key, or the specified Object if no such mapping has been made.
    int
    indexOfKey(int key)
    Returns the index for which keyAt(int) would return the specified key, or a negative number if the specified key is not mapped.
    int
    indexOfValue(E value)
    Returns an index for which valueAt(int) would return the specified value, or a negative number if no keys map to the specified value.
    int
    indexOfValueByValue(E value)
    Returns an index for which valueAt(int) would return the specified value, or a negative number if no keys map to the specified value.
    int
    keyAt(int index)
    Given an index in the range 0...size()-1, returns the key from the indexth key-value mapping that this SparseArray stores.
    void
    put(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.
    void
    remove(int key)
    Alias for delete(int).
    void
    removeAt(int index)
    Removes the mapping at the specified index.
    void
    removeAtRange(int index, int size)
    Remove a range of mappings as a batch.
    E
    removeReturnOld(int key)
    Removes the mapping from the specified key, if there was any, returning the old value.
    void
    setValueAt(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.
    int
    size()
    Returns the number of key-value mappings that this SparseArray currently stores.
    String
    toString()
    E
    valueAt(int index)
    Given an index in the range 0...size()-1, returns the value from the indexth key-value mapping that this SparseArray stores.

    Methods inherited from class Object

    equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

  • Field Details

    • EMPTY_CHARS

      private static final char[] EMPTY_CHARS
      The empty key array.

    • EMPTY_OBJECTS

      private static final Object[] EMPTY_OBJECTS
      The empty value array.

    • DELETED

      private static final Object DELETED
      The marker of a deleted value.

    • mGarbage

      private boolean mGarbage
      True when deleted entries await collection.

    • mKeys

      private char[] mKeys
      The array of keys.

    • mValues

      private Object[] mValues
      The array of values.

    • mSize

      private int mSize
      The number of entries.

  • Constructor Details

    • SparseArray

      public SparseArray()
      Creates a new SparseArray containing no mappings.

    • SparseArray

      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.
      Parameters:
      initialCapacity - mappings to preallocate backing arrays for; 0 allocates none

    • SparseArray

      private SparseArray(SparseArray<E> source)
      Copy constructor.
      Parameters:
      source - the array to copy

  • Method Details

    • clone

      public SparseArray<E> clone()
      Returns a shallow copy of this SparseArray with deep-copied key and value arrays so the clone's internal arrays are independent of the original's.
      Overrides:
      clone in class Object
      Returns:
      a clone of this SparseArray

    • get

      public E get(int key)
      Object mapped from the specified key, or null if no such mapping has been made.
      Parameters:
      key - 0 MIN, 65535 MAX
      Returns:
      the value stored for key, or null if the key is not mapped

    • get

      public E get(int key, E valueIfKeyNotFound)
      Object mapped from the specified key, or the specified Object if no such mapping has been made.
      Parameters:
      key - 0 MIN, 65535 MAX
      valueIfKeyNotFound - returned in place of null when the key is not mapped
      Returns:
      the value stored for key, or valueIfKeyNotFound if the key is not mapped

    • delete

      public void delete(int key)
      Removes the mapping from the specified key, if there was any.
      Parameters:
      key - 0 MIN, 65535 MAX

    • removeReturnOld

      public E removeReturnOld(int key)
      Removes the mapping from the specified key, if there was any, returning the old value.
      Parameters:
      key - 0 MIN, 65535 MAX
      Returns:
      the value removed from the array, or null if the key was not mapped

    • remove

      public void remove(int key)
      Alias for delete(int).
      Parameters:
      key - 0 MIN, 65535 MAX

    • removeAt

      public void removeAt(int index)
      Removes the mapping at the specified index.

      For indices outside of the range 0...size()-1, a ArrayIndexOutOfBoundsException is thrown.

      Parameters:
      index - position of the mapping to drop, 0 to size()-1

    • removeAtRange

      public void removeAtRange(int index, int size)
      Remove a range of mappings as a batch.
      Parameters:
      index - Index to begin at
      size - Number of mappings to remove

      For indices outside of the range 0...size()-1, the behavior is undefined.

    • gc

      private void gc()
      Removes the deleted entries.

    • put

      public void put(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.
      Parameters:
      key - 0 MIN, 65535 MAX
      value - the element to store, replacing any existing mapping for key

    • size

      public int size()
      Returns the number of key-value mappings that this SparseArray currently stores.
      Returns:
      the number of live mappings, 0 for an empty array

    • keyAt

      public int keyAt(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.

      For indices outside of the range 0...size()-1, a ArrayIndexOutOfBoundsException is thrown.

      Parameters:
      index - position of the mapping, 0 to size()-1
      Returns:
      the key at that position, in ascending key order

    • valueAt

      public E valueAt(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.

      For indices outside of the range 0...size()-1, a ArrayIndexOutOfBoundsException is thrown.

      Parameters:
      index - position of the mapping, 0 to size()-1
      Returns:
      the element stored at that position

    • setValueAt

      public void setValueAt(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.

      For indices outside of the range 0...size()-1, a ArrayIndexOutOfBoundsException is thrown.

      Parameters:
      index - position of the mapping, 0 to size()-1
      value - the element to store there, leaving the key unchanged

    • indexOfKey

      public int indexOfKey(int key)
      Returns the index for which keyAt(int) would return the specified key, or a negative number if the specified key is not mapped.
      Parameters:
      key - 0 MIN, 65535 MAX
      Returns:
      the position of the mapping, or a negative value if key is not mapped

    • indexOfValue

      public int indexOfValue(E value)
      Returns an index for which valueAt(int) would return the specified value, 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' indexOf methods, this method compares values using == rather than equals.

      Parameters:
      value - the element to look for, compared by reference
      Returns:
      the position of one mapping holding it, or -1 if none does

    • indexOfValueByValue

      public int indexOfValueByValue(E value)
      Returns an index for which valueAt(int) would return the specified value, 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 this method uses equals unlike indexOfValue.

      Parameters:
      value - the element to look for, compared with equals()
      Returns:
      the position of one mapping equal to it, or -1 if none is

    • clear

      public void clear()
      Removes all key-value mappings from this SparseArray.

    • append

      public void append(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.
      Parameters:
      key - 0 MIN, 65535 MAX
      value - the element to store, replacing any existing mapping for key

    • toString

      public String toString()

      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.

      Overrides:
      toString in class Object