Package android.util

Class ArrayMap<K,​V>

  • All Implemented Interfaces:
    Map<K,​V>
    public final class ArrayMap<K,​V>
extends Object
implements Map<K,​V>
    ArrayMap is a generic key->value mapping data structure that is designed to be more memory efficient than a traditional HashMap. It keeps its mappings in an array data structure -- an integer array of hash codes for each item, and an Object array of the key/value pairs. This allows it to avoid having to create an extra object for every entry put in to the map, and it also tries to control the growth of the size of these arrays more aggressively (since growing them only requires copying the entries in the array, not rebuilding a hash map).

    Note that this 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%.

    Because this container is intended to better balance memory use, unlike most other standard Java containers it will shrink its array as items are removed from it. Currently you have no control over this shrinking -- if you set a capacity and then remove an item, it may reduce the capacity to better match the current size. In the future an explicit call to set the capacity should turn off this aggressive shrinking behavior.

    • Nested Class Summary

      • Nested classes/interfaces inherited from interface java.util.Map

        Map.Entry<K,​V>

    • Field Summary

      Fields 
      Modifier and Type Field Description
      static ArrayMap EMPTY  

    • Constructor Summary

      Constructors 
      Constructor Description
      ArrayMap()
      Create a new empty ArrayMap.
      ArrayMap​(int capacity)
      Create a new ArrayMap with a given initial capacity.
      ArrayMap​(ArrayMap<K,​V> map)
      Create a new ArrayMap with the mappings from the given ArrayMap.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void append​(K key, V value)
      Special fast path for appending items to the end of the array without validation.
      void clear()
      Make the array map empty.
      boolean containsAll​(Collection<?> collection)
      Determine if the array map contains all of the keys in the given collection.
      boolean containsKey​(Object key)
      Check whether a key exists in the array.
      boolean containsValue​(Object value)
      Check whether a value exists in the array.
      void ensureCapacity​(int minimumCapacity)
      Ensure the array map can hold at least minimumCapacity items.
      Set<Map.Entry<K,​V>> entrySet()
      Return a Set for iterating over and interacting with all mappings in the array map.
      boolean equals​(Object object)
      Compares this instance with the specified object and indicates if they are equal.
      void erase()  
      V get​(Object key)
      Retrieve a value from the array.
      int hashCode()
      Returns an integer hash code for this object.
      int indexOfKey​(Object key)
      Returns the index of a key in the set.
      boolean isEmpty()
      Return true if the array map contains no items.
      K keyAt​(int index)
      Return the key at the given index in the array.
      Set<K> keySet()
      Return a Set for iterating over and interacting with all keys in the array map.
      V put​(K key, V value)
      Add a new value to the array map.
      void putAll​(ArrayMap<? extends K,​? extends V> array)
      Perform a put(Object, Object) of all key/value pairs in array
      void putAll​(Map<? extends K,​? extends V> map)
      Perform a put(Object, Object) of all key/value pairs in map
      V remove​(Object key)
      Remove an existing key from the array map.
      boolean removeAll​(Collection<?> collection)
      Remove all keys in the array map that exist in the given collection.
      V removeAt​(int index)
      Remove the key/value mapping at the given index.
      boolean retainAll​(Collection<?> collection)
      Remove all keys in the array map that do not exist in the given collection.
      V setValueAt​(int index, V value)
      Set the value at a given index in the array.
      int size()
      Return the number of items in this array map.
      String toString()
      Returns a string containing a concise, human-readable description of this object.
      void validate()
      The use of the append(K, V) function can result in invalid array maps, in particular an array map where the same key appears multiple times.
      V valueAt​(int index)
      Return the value at the given index in the array.
      Collection<V> values()
      Return a Collection for iterating over and interacting with all values in the array map.

    • Field Detail

      • EMPTY

        public static final ArrayMap EMPTY

    • Constructor Detail

      • ArrayMap

        public ArrayMap()
        Create a new empty ArrayMap. The default capacity of an array map is 0, and will grow once items are added to it.

      • ArrayMap

        public ArrayMap​(int capacity)
        Create a new ArrayMap with a given initial capacity.

      • ArrayMap

        public ArrayMap​(ArrayMap<K,​V> map)
        Create a new ArrayMap with the mappings from the given ArrayMap.

    • Method Detail

      • erase

        public void erase()

      • ensureCapacity

        public void ensureCapacity​(int minimumCapacity)
        Ensure the array map can hold at least minimumCapacity items.

      • containsKey

        public boolean containsKey​(Object key)
        Check whether a key exists in the array.
        Specified by:
        containsKey in interface Map<K,​V>
        Parameters:
        key - The key to search for.
        Returns:
        Returns true if the key exists, else false.

      • indexOfKey

        public int indexOfKey​(Object key)
        Returns the index of a key in the set.
        Parameters:
        key - The key to search for.
        Returns:
        Returns the index of the key if it exists, else a negative integer.

      • containsValue

        public boolean containsValue​(Object value)
        Check whether a value exists in the array. This requires a linear search through the entire array.
        Specified by:
        containsValue in interface Map<K,​V>
        Parameters:
        value - The value to search for.
        Returns:
        Returns true if the value exists, else false.

      • get

        public V get​(Object key)
        Retrieve a value from the array.
        Specified by:
        get in interface Map<K,​V>
        Parameters:
        key - The key of the value to retrieve.
        Returns:
        Returns the value associated with the given key, or null if there is no such key.

      • keyAt

        public K keyAt​(int index)
        Return the key at the given index in the array.
        Parameters:
        index - The desired index, must be between 0 and size()-1.
        Returns:
        Returns the key stored at the given index.

      • valueAt

        public V valueAt​(int index)
        Return the value at the given index in the array.
        Parameters:
        index - The desired index, must be between 0 and size()-1.
        Returns:
        Returns the value stored at the given index.

      • setValueAt

        public V setValueAt​(int index,
                    V value)
        Set the value at a given index in the array.
        Parameters:
        index - The desired index, must be between 0 and size()-1.
        value - The new value to store at this index.
        Returns:
        Returns the previous value at the given index.

      • isEmpty

        public boolean isEmpty()
        Return true if the array map contains no items.
        Specified by:
        isEmpty in interface Map<K,​V>
        Returns:
        true if this map has no elements, false otherwise.
        See Also:
        Map.size()

      • put

        public V put​(K key,
             V value)
        Add a new value to the array map.
        Specified by:
        put in interface Map<K,​V>
        Parameters:
        key - The key under which to store the value. If this key already exists in the array, its value will be replaced.
        value - The value to store for the given key.
        Returns:
        Returns the old value that was stored for the given key, or null if there was no such key.

      • append

        public void append​(K key,
                   V value)
        Special fast path for appending items to the end of the array without validation. The array must already be large enough to contain the item.

      • validate

        public void validate()
        The use of the append(K, V) function can result in invalid array maps, in particular an array map where the same key appears multiple times. This function verifies that the array map is valid, throwing IllegalArgumentException if a problem is found. The main use for this method is validating an array map after unpacking from an IPC, to protect against malicious callers.

      • putAll

        public void putAll​(ArrayMap<? extends K,​? extends V> array)
        Perform a put(Object, Object) of all key/value pairs in array
        Parameters:
        array - The array whose contents are to be retrieved.

      • remove

        public V remove​(Object key)
        Remove an existing key from the array map.
        Specified by:
        remove in interface Map<K,​V>
        Parameters:
        key - The key of the mapping to remove.
        Returns:
        Returns the value that was stored under the key, or null if there was no such key.

      • removeAt

        public V removeAt​(int index)
        Remove the key/value mapping at the given index.
        Parameters:
        index - The desired index, must be between 0 and size()-1.
        Returns:
        Returns the value that was stored at this index.

      • size

        public int size()
        Return the number of items in this array map.
        Specified by:
        size in interface Map<K,​V>
        Returns:
        the number of mappings in this Map.

      • equals

        public boolean equals​(Object object)
        Compares this instance with the specified object and indicates if they are equal. In order to be equal, o must represent the same object as this instance using a class-specific comparison. The general contract is that this comparison should be reflexive, symmetric, and transitive. Also, no object reference other than null is equal to null.

        The default implementation returns true only if this == o. See Writing a correct equals method if you intend implementing your own equals method.

        The general contract for the equals and Object.hashCode() methods is that if equals returns true for any two objects, then hashCode() must return the same value for these objects. This means that subclasses of Object usually override either both methods or neither of them.

        This implementation returns false if the object is not a map, or if the maps have different sizes. Otherwise, for each key in this map, values of both maps are compared. If the values for any key are not equal, the method returns false, otherwise it returns true.

        Specified by:
        equals in interface Map<K,​V>
        Overrides:
        equals in class Object
        Parameters:
        object - the object to compare this instance with.
        Returns:
        true if the specified object is equal to this Object; false otherwise.
        See Also:
        Object.hashCode()

      • hashCode

        public int hashCode()
        Returns an integer hash code for this object. By contract, any two objects for which Object.equals(java.lang.Object) returns true must return the same hash code value. This means that subclasses of Object usually override both methods or neither method.

        Note that hash values must not change over time unless information used in equals comparisons also changes.

        See Writing a correct hashCode method if you intend implementing your own hashCode method.

        Specified by:
        hashCode in interface Map<K,​V>
        Overrides:
        hashCode in class Object
        Returns:
        this object's hash code.
        See Also:
        Object.equals(java.lang.Object)

      • toString

        public String toString()
        Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation is equivalent to the following expression: 
           getClass().getName() + '@' + Integer.toHexString(hashCode())

        See Writing a useful toString method if you intend implementing your own toString method.

        This implementation composes a string by iterating over its mappings. If this map contains itself as a key or a value, the string "(this Map)" will appear in its place.

        Overrides:
        toString in class Object
        Returns:
        a printable representation of this object.

      • containsAll

        public boolean containsAll​(Collection<?> collection)
        Determine if the array map contains all of the keys in the given collection.
        Parameters:
        collection - The collection whose contents are to be checked against.
        Returns:
        Returns true if this array map contains a key for every entry in collection, else returns false.

      • putAll

        public void putAll​(Map<? extends K,​? extends V> map)
        Perform a put(Object, Object) of all key/value pairs in map
        Specified by:
        putAll in interface Map<K,​V>
        Parameters:
        map - The map whose contents are to be retrieved.

      • removeAll

        public boolean removeAll​(Collection<?> collection)
        Remove all keys in the array map that exist in the given collection.
        Parameters:
        collection - The collection whose contents are to be used to remove keys.
        Returns:
        Returns true if any keys were removed from the array map, else false.

      • retainAll

        public boolean retainAll​(Collection<?> collection)
        Remove all keys in the array map that do not exist in the given collection.
        Parameters:
        collection - The collection whose contents are to be used to determine which keys to keep.
        Returns:
        Returns true if any keys were removed from the array map, else false.

      • entrySet

        public Set<Map.Entry<K,​V>> entrySet()
        Return a Set for iterating over and interacting with all mappings in the array map.

        Note: this is a very inefficient way to access the array contents, it requires generating a number of temporary objects and allocates additional state information associated with the container that will remain for the life of the container.

        Note:

        the semantics of this Set are subtly different than that of a HashMap: most important, the Map.Entry object returned by its iterator is a single object that exists for the entire iterator, so you can not hold on to it after calling Iterator.next.

        Specified by:
        entrySet in interface Map<K,​V>
        Returns:
        a set of the mappings

      • keySet

        public Set<K> keySet()
        Return a Set for iterating over and interacting with all keys in the array map.

        Note: this is a fairly inefficient way to access the array contents, it requires generating a number of temporary objects and allocates additional state information associated with the container that will remain for the life of the container.

        Specified by:
        keySet in interface Map<K,​V>
        Returns:
        a set of the keys.

      • values

        public Collection<V> values()
        Return a Collection for iterating over and interacting with all values in the array map.

        Note: this is a fairly inefficient way to access the array contents, it requires generating a number of temporary objects and allocates additional state information associated with the container that will remain for the life of the container.

        Specified by:
        values in interface Map<K,​V>
        Returns:
        a collection of the values contained in this map.