Package com.badlogic.gdx.utils

Class ObjectMap<K,​V>

  • All Implemented Interfaces:
    java.lang.Iterable<ObjectMap.Entry<K,​V>>
    Direct Known Subclasses:
    IdentityMap, OrderedMap
    public class ObjectMap<K,​V>
extends java.lang.Object
implements java.lang.Iterable<ObjectMap.Entry<K,​V>>
    An unordered map where the keys and values are objects. Null keys are not allowed. No allocation is done except when growing the table size.

    This class performs fast contains and remove (typically O(1), worst case O(n) but that is rare in practice). Add may be slightly slower, depending on hash collisions. Hashcodes are rehashed to reduce collisions and the need to resize. Load factors greater than 0.91 greatly increase the chances to resize to the next higher POT size.

    Unordered sets and maps are not designed to provide especially fast iteration. Iteration is faster with OrderedSet and OrderedMap.

    This implementation uses linear probing with the backward shift algorithm for removal. Hashcodes are rehashed using Fibonacci hashing, instead of the more common power-of-two mask, to better distribute poor hashCodes (see Malte Skarupke's blog post). Linear probing continues to work even when all hashCodes collide, just more slowly.

    • Field Summary

      Fields 
      Modifier and Type Field Description
      protected int mask
      A bitmask used to confine hashcodes to the size of the table.
      protected int shift
      Used by place(Object) to bit shift the upper bits of a long into a usable range (>= 0 and <= mask).
      int size  

    • Constructor Summary

      Constructors 
      Constructor Description
      ObjectMap()
      Creates a new map with an initial capacity of 51 and a load factor of 0.8.
      ObjectMap​(int initialCapacity)
      Creates a new map with a load factor of 0.8.
      ObjectMap​(int initialCapacity, float loadFactor)
      Creates a new map with the specified initial capacity and load factor.
      ObjectMap​(ObjectMap<? extends K,​? extends V> map)
      Creates a new map identical to the specified map.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void clear()  
      void clear​(int maximumCapacity)
      Clears the map and reduces the size of the backing arrays to be the specified capacity / loadFactor, if they are larger.
      boolean containsKey​(K key)  
      boolean containsValue​(java.lang.Object value, boolean identity)
      Returns true if the specified value is in the map.
      void ensureCapacity​(int additionalCapacity)
      Increases the size of the backing array to accommodate the specified number of additional items / loadFactor.
      ObjectMap.Entries<K,​V> entries()
      Returns an iterator for the entries in the map.
      boolean equals​(java.lang.Object obj)  
      boolean equalsIdentity​(java.lang.Object obj)
      Uses == for comparison of each value.
      K findKey​(java.lang.Object value, boolean identity)
      Returns the key for the specified value, or null if it is not in the map.
      V get​(K key, V defaultValue)
      Returns the value for the specified key, or the default value if the key is not in the map.
      <T extends K>
      V      		 get​(T key)
      Returns the value for the specified key, or null if the key is not in the map.
      int hashCode()  
      boolean isEmpty()
      Returns true if the map is empty.
      ObjectMap.Entries<K,​V> iterator()  
      ObjectMap.Keys<K> keys()
      Returns an iterator for the keys in the map.
      boolean notEmpty()
      Returns true if the map has one or more items.
      protected int place​(K item)
      Returns an index >= 0 and <= mask for the specified item.
      V put​(K key, V value)
      Returns the old value associated with the specified key, or null.
      void putAll​(ObjectMap<? extends K,​? extends V> map)  
      V remove​(K key)
      Returns the value for the removed key, or null if the key is not in the map.
      void shrink​(int maximumCapacity)
      Reduces the size of the backing arrays to be the specified capacity / loadFactor, or less.
      java.lang.String toString()  
      java.lang.String toString​(java.lang.String separator)  
      protected java.lang.String toString​(java.lang.String separator, boolean braces)  
      ObjectMap.Values<V> values()
      Returns an iterator for the values in the map.

      • Methods inherited from class java.lang.Object

        clone, finalize, getClass, notify, notifyAll, wait, wait, wait

      • Methods inherited from interface java.lang.Iterable

        forEach, spliterator

    • Field Detail

      • size

        public int size

      • shift

        protected int shift
        Used by place(Object) to bit shift the upper bits of a long into a usable range (>= 0 and <= mask). The shift can be negative, which is convenient to match the number of bits in mask: if mask is a 7-bit number, a shift of -7 shifts the upper 7 bits into the lowest 7 positions. This class sets the shift > 32 and < 64, which if used with an int will still move the upper bits of an int to the lower bits due to Java's implicit modulus on shifts.

        mask can also be used to mask the low bits of a number, which may be faster for some hashcodes, if place(Object) is overridden.

      • mask

        protected int mask
        A bitmask used to confine hashcodes to the size of the table. Must be all 1 bits in its low positions, ie a power of two minus 1. If place(Object) is overriden, this can be used instead of shift to isolate usable bits of a hash.

    • Constructor Detail

      • ObjectMap

        public ObjectMap()
        Creates a new map with an initial capacity of 51 and a load factor of 0.8.

      • ObjectMap

        public ObjectMap​(int initialCapacity)
        Creates a new map with a load factor of 0.8.
        Parameters:
        initialCapacity - The backing array size is initialCapacity / loadFactor, increased to the next power of two.

      • ObjectMap

        public ObjectMap​(int initialCapacity,
                 float loadFactor)
        Creates a new map with the specified initial capacity and load factor. This map will hold initialCapacity items before growing the backing table.
        Parameters:
        initialCapacity - The backing array size is initialCapacity / loadFactor, increased to the next power of two.

      • ObjectMap

        public ObjectMap​(ObjectMap<? extends K,​? extends V> map)
        Creates a new map identical to the specified map.

    • Method Detail

      • place

        protected int place​(K item)
        Returns an index >= 0 and <= mask for the specified item.

        The default implementation uses Fibonacci hashing on the item's Object.hashCode(): the hashcode is multiplied by a long constant (2 to the 64th, divided by the golden ratio) then the uppermost bits are shifted into the lowest positions to obtain an index in the desired range. Multiplication by a long may be slower than int (eg on GWT) but greatly improves rehashing, allowing even very poor hashcodes, such as those that only differ in their upper bits, to be used without high collision rates. Fibonacci hashing has increased collision rates when all or most hashcodes are multiples of larger Fibonacci numbers (see Malte Skarupke's blog post).

        This method can be overriden to customizing hashing. This may be useful eg in the unlikely event that most hashcodes are Fibonacci numbers, if keys provide poor or incorrect hashcodes, or to simplify hashing if keys provide high quality hashcodes and don't need Fibonacci hashing: return item.hashCode() & mask;

      • put

        @Null
public V put​(K key,
             @Null
             V value)
        Returns the old value associated with the specified key, or null.

      • putAll

        public void putAll​(ObjectMap<? extends K,​? extends V> map)

      • get

        @Null
public <T extends K> V get​(T key)
        Returns the value for the specified key, or null if the key is not in the map.

      • get

        public V get​(K key,
             @Null
             V defaultValue)
        Returns the value for the specified key, or the default value if the key is not in the map.

      • remove

        @Null
public V remove​(K key)
        Returns the value for the removed key, or null if the key is not in the map.

      • notEmpty

        public boolean notEmpty()
        Returns true if the map has one or more items.

      • isEmpty

        public boolean isEmpty()
        Returns true if the map is empty.

      • shrink

        public void shrink​(int maximumCapacity)
        Reduces the size of the backing arrays to be the specified capacity / loadFactor, or less. If the capacity is already less, nothing is done. If the map contains more items than the specified capacity, the next highest power of two capacity is used instead.

      • clear

        public void clear​(int maximumCapacity)
        Clears the map and reduces the size of the backing arrays to be the specified capacity / loadFactor, if they are larger.

      • clear

        public void clear()

      • containsValue

        public boolean containsValue​(@Null
                             java.lang.Object value,
                             boolean identity)
        Returns true if the specified value is in the map. Note this traverses the entire map and compares every value, which may be an expensive operation.
        Parameters:
        identity - If true, uses == to compare the specified value with values in the map. If false, uses equals(Object).

      • containsKey

        public boolean containsKey​(K key)

      • findKey

        @Null
public K findKey​(@Null
                 java.lang.Object value,
                 boolean identity)
        Returns the key for the specified value, or null if it is not in the map. Note this traverses the entire map and compares every value, which may be an expensive operation.
        Parameters:
        identity - If true, uses == to compare the specified value with values in the map. If false, uses equals(Object).

      • ensureCapacity

        public void ensureCapacity​(int additionalCapacity)
        Increases the size of the backing array to accommodate the specified number of additional items / loadFactor. Useful before adding many items to avoid multiple backing array resizes.

      • hashCode

        public int hashCode()
        Overrides:
        hashCode in class java.lang.Object

      • equals

        public boolean equals​(java.lang.Object obj)
        Overrides:
        equals in class java.lang.Object

      • equalsIdentity

        public boolean equalsIdentity​(@Null
                              java.lang.Object obj)
        Uses == for comparison of each value.

      • toString

        public java.lang.String toString​(java.lang.String separator)

      • toString

        public java.lang.String toString()
        Overrides:
        toString in class java.lang.Object

      • toString

        protected java.lang.String toString​(java.lang.String separator,
                                    boolean braces)

      • iterator

        public ObjectMap.Entries<K,​V> iterator()
        Specified by:
        iterator in interface java.lang.Iterable<K>

      • keys

        public ObjectMap.Keys<K> keys()
        Returns an iterator for the keys in the map. Remove is supported.

        If Collections.allocateIterators is false, the same iterator instance is returned each time this method is called. Use the ObjectMap.Keys constructor for nested or multithreaded iteration.