Package net.i2p.router.crypto.ratchet

Class SparseArray<E>

java.lang.Object
net.i2p.router.crypto.ratchet.SparseArray<E>
All Implemented Interfaces:
Cloneable
class SparseArray<E>
extends Object
implements Cloneable
SparseArray maps integers to Objects and, unlike a normal array of Objects, its indices can contain gaps. SparseArray is intended to be more memory-efficient than a HashMap, 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 HashMap because 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 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 the keys using keyAt(int) with ascending values of the index returns the keys in ascending order. In the case of valueAt(int), the values corresponding to the keys are returned in ascending order.

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

  • Constructor Summary

    Constructors 
    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.

  • 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()  
    void delete​(int key)
    Removes the mapping from the specified key, if there was any.
    E get​(int key)
    Gets the Object mapped from the specified key, or null if no such mapping has been made.
    E get​(int key, E valueIfKeyNotFound)
    Gets the 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 java.lang.Object

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

  • 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.

  • Method Details

    • clone

      public SparseArray<E> clone()
      Overrides:
      clone in class Object

    • get

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

    • get

      public E get​(int key, E valueIfKeyNotFound)
      Gets the Object mapped from the specified key, or the specified Object if no such mapping has been made.
      Parameters:
      key - 0 MIN, 65535 MAX

    • 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

    • remove

      public void remove​(int key)
      Alias for delete(int).

    • 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.

    • 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.

    • 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

    • size

      public int size()
      Returns the number of key-value mappings that this SparseArray currently stores.

    • 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.

    • 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.

    • 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.

    • 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

    • 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.

    • 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.

    • 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

    • 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