Class AbstractMap<K,V>

java.lang.Object
java.util.AbstractMap<K,V>
All Implemented Interfaces:
Map<K,V>
Direct Known Subclasses:
HashMap, IdentityHashMap, TreeMap
public abstract class AbstractMap<K,V> extends Object implements Map<K,V>

This class is an abstract implementation of the Map interface. This implementation does not support adding. A subclass must implement the abstract method entrySet().

Since

1.2

  • Nested Class Summary

    Nested Classes
    Modifier and Type
    Class
    Description
    static class 
    AbstractMap.SimpleEntry<K,V>
    A key-value mapping.
    static class 
    AbstractMap.SimpleImmutableEntry<K,V>
    An immutable key-value mapping.

    Nested classes/interfaces inherited from interface Map

    Map.Entry<K,V>

  • Constructor Summary

    Constructors
    Modifier
    Constructor
    Description
    protected
    AbstractMap()
    Constructs a new instance of this AbstractMap.

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    clear()
    Removes all elements from this map, leaving it empty.
    boolean
    containsKey(Object key)
    Returns whether this map contains the specified key.
    boolean
    containsValue(Object value)
    Returns whether this map contains the specified value.
    abstract Set<Map.Entry<K,V>>
    entrySet()
    Returns a set containing all of the mappings in this map.
    boolean
    equals(Object object)
    Compares the specified object to this instance, and returns true if the specified object is a map and both maps contain the same mappings.
    V
    get(Object key)
    Returns the value of the mapping with the specified key.
    int
    hashCode()
    Returns the hash code for this object.
    boolean
    isEmpty()
    Returns whether this map is empty.
    Set<K>
    keySet()
    Returns a set of the keys contained in this map.
    V
    put(K key, V value)
    Maps the specified key to the specified value.
    void
    putAll(Map<? extends K, ? extends V> map)
    Copies every mapping in the specified map to this map.
    V
    remove(Object key)
    Removes a mapping with the specified key from this Map.
    int
    size()
    Returns the number of elements in this map.
    String
    toString()
    Returns the string representation of this map.
    Collection<V>
    values()
    Returns a collection of the values contained in this map.

    Methods inherited from class Object

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

  • Constructor Details

    • AbstractMap

      protected AbstractMap()
      Constructs a new instance of this AbstractMap.

  • Method Details

    • clear

      public void clear()

      Removes all elements from this map, leaving it empty.

      Throws
      • UnsupportedOperationException: if removing from this map is not supported.
      See also

      • #isEmpty()

      • #size()

      Specified by:
      clear in interface Map<K,V>

    • containsKey

      public boolean containsKey(Object key)

      Returns whether this map contains the specified key.

      Parameters
      • key: the key to search for.
      Returns
      Specified by:
      containsKey in interface Map<K,V>
      Returns:
      true if this map contains the specified key, false otherwise.

    • containsValue

      public boolean containsValue(Object value)

      Returns whether this map contains the specified value.

      Parameters
      • value: the value to search for.
      Returns
      Specified by:
      containsValue in interface Map<K,V>
      Returns:
      true if this map contains the specified value, false otherwise.

    • entrySet

      public abstract Set<Map.Entry<K,V>> entrySet()

      Returns a set containing all of the mappings in this map. Each mapping is an instance of Map.Entry. As the set is backed by this map, changes in one will be reflected in the other.

      Returns

      a set of the mappings.

      Specified by:
      entrySet in interface Map<K,V>

    • equals

      public boolean equals(Object object)

      Compares the specified object to this instance, and returns true if the specified object is a map and both maps contain the same mappings.

      Parameters
      • object: the object to compare with this object.
      Returns
      Specified by:
      equals in interface Map<K,V>
      Overrides:
      equals in class Object
      Returns:

      boolean true if the object is the same as this object, and false if it is different from this object.

      See also

      • #hashCode()

      • #entrySet()

    • get

      public V get(Object key)

      Returns the value of the mapping with the specified key.

      Parameters
      • key: the key.
      Returns
      Specified by:
      get in interface Map<K,V>
      Returns:
      the value of the mapping with the specified key, or null if no mapping for the specified key is found.

    • hashCode

      public int hashCode()

      Returns the hash code for this object. Objects which are equal must return the same value for this method.

      Returns

      the hash code of this object.

      See also
      • #equals(Object)
      Specified by:
      hashCode in interface Map<K,V>
      Overrides:
      hashCode in class Object

    • isEmpty

      public boolean isEmpty()

      Returns whether this map is empty.

      Returns
      Specified by:
      isEmpty in interface Map<K,V>
      Returns:

      true if this map has no elements, false otherwise.

      See also
      • #size()

    • keySet

      public Set<K> keySet()

      Returns a set of the keys contained in this map. The set is backed by this map so changes to one are reflected by the other. The returned set does not support adding.

      Returns

      a set of the keys.

      Specified by:
      keySet in interface Map<K,V>

    • put

      public V put(K key, V value)

      Maps the specified key to the specified value.

      Parameters

      • key: the key.

      • value: the value.

      Returns
      Specified by:
      put in interface Map<K,V>
      Returns:

      the value of any previous mapping with the specified key or null if there was no mapping.

      Throws

      • UnsupportedOperationException: if adding to this map is not supported.

      • ClassCastException: @throws ClassCastException if the class of the key or value is inappropriate for this map.

      • IllegalArgumentException: if the key or value cannot be added to this map.

      • NullPointerException: @throws NullPointerException if the key or value is null and this Map does not support null keys or values.

    • putAll

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

      Copies every mapping in the specified map to this map.

      Parameters
      • map: the map to copy mappings from.
      Throws

      • UnsupportedOperationException: if adding to this map is not supported.

      • ClassCastException: @throws ClassCastException if the class of a key or value is inappropriate for this map.

      • IllegalArgumentException: if a key or value cannot be added to this map.

      • NullPointerException: @throws NullPointerException if a key or value is null and this map does not support null keys or values.

      Specified by:
      putAll in interface Map<K,V>

    • remove

      public V remove(Object key)

      Removes a mapping with the specified key from this Map.

      Parameters
      • key: the key of the mapping to remove.
      Returns
      Specified by:
      remove in interface Map<K,V>
      Returns:

      the value of the removed mapping or null if no mapping for the specified key was found.

      Throws
      • UnsupportedOperationException: if removing from this map is not supported.

    • size

      public int size()

      Returns the number of elements in this map.

      Returns

      the number of elements in this map.

      Specified by:
      size in interface Map<K,V>

    • toString

      public String toString()

      Returns the string representation of this map.

      Returns

      the string representation of this map.

      Overrides:
      toString in class Object

    • values

      public Collection<V> values()

      Returns a collection of the values contained in this map. The collection is backed by this map so changes to one are reflected by the other. The collection supports remove, removeAll, retainAll and clear operations, and it does not support add or addAll operations.

      This method returns a collection which is the subclass of AbstractCollection. The iterator method of this subclass returns a "wrapper object" over the iterator of map's entrySet(). The size method wraps the map's size method and the contains method wraps the map's containsValue method.

      The collection is created when this method is called for the first time and returned in response to all subsequent calls. This method may return different collections when multiple concurrent calls occur to this method, since no synchronization is performed.

      Returns

      a collection of the values contained in this map.

      Specified by:
      values in interface Map<K,V>