java.util
Class AbstractMap<K,V>

java.lang.Object sample code for java.lang.Object definition code for java.lang.Object 
  extended by java.util.AbstractMap<K,V>
All Implemented Interfaces:
Map sample code for java.util.Map definition code for java.util.Map <K,V>
Direct Known Subclasses:
ConcurrentHashMap sample code for java.util.concurrent.ConcurrentHashMap definition code for java.util.concurrent.ConcurrentHashMap , EnumMap sample code for java.util.EnumMap definition code for java.util.EnumMap , HashMap sample code for java.util.HashMap definition code for java.util.HashMap , IdentityHashMap sample code for java.util.IdentityHashMap definition code for java.util.IdentityHashMap , TreeMap sample code for java.util.TreeMap definition code for java.util.TreeMap , WeakHashMap sample code for java.util.WeakHashMap definition code for java.util.WeakHashMap

public abstract class AbstractMap<K,V>
extends Object sample code for java.lang.Object definition code for java.lang.Object
implements Map sample code for java.util.Map definition code for java.util.Map <K,V>

This class provides a skeletal implementation of the Map interface, to minimize the effort required to implement this interface.

To implement an unmodifiable map, the programmer needs only to extend this class and provide an implementation for the entrySet method, which returns a set-view of the map's mappings. Typically, the returned set will, in turn, be implemented atop AbstractSet. This set should not support the add or remove methods, and its iterator should not support the remove method.

To implement a modifiable map, the programmer must additionally override this class's put method (which otherwise throws an UnsupportedOperationException), and the iterator returned by entrySet().iterator() must additionally implement its remove method.

The programmer should generally provide a void (no argument) and map constructor, as per the recommendation in the Map interface specification.

The documentation for each non-abstract methods in this class describes its implementation in detail. Each of these methods may be overridden if the map being implemented admits a more efficient implementation.

This class is a member of the Java Collections Framework.

Since:
1.2
See Also:
Map sample code for java.util.Map definition code for java.util.Map , Collection sample code for java.util.Collection definition code for java.util.Collection

Nested Class Summary
 
Nested classes/interfaces inherited from interface java.util.Map sample code for java.util.Map definition code for java.util.Map
Map.Entry sample code for java.util.Map.Entry definition code for java.util.Map.Entry <K,V>
 
Constructor Summary
protected AbstractMap sample code for java.util.AbstractMap.AbstractMap() definition code for java.util.AbstractMap.AbstractMap() ()
          Sole constructor.
 
Method Summary
 void clear sample code for java.util.AbstractMap.clear() definition code for java.util.AbstractMap.clear() ()
          Removes all mappings from this map (optional operation).
protected  Object sample code for java.lang.Object definition code for java.lang.Object clone sample code for java.util.AbstractMap.clone() definition code for java.util.AbstractMap.clone() ()
          Returns a shallow copy of this AbstractMap instance: the keys and values themselves are not cloned.
 boolean containsKey sample code for java.util.AbstractMap.containsKey(java.lang.Object) definition code for java.util.AbstractMap.containsKey(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  key)
          Returns true if this map contains a mapping for the specified key.
 boolean containsValue sample code for java.util.AbstractMap.containsValue(java.lang.Object) definition code for java.util.AbstractMap.containsValue(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  value)
          Returns true if this map maps one or more keys to this value.
abstract  Set sample code for java.util.Set definition code for java.util.Set <Map.Entry sample code for java.util.Map.Entry definition code for java.util.Map.Entry <K,V>> entrySet sample code for java.util.AbstractMap.entrySet() definition code for java.util.AbstractMap.entrySet() ()
          Returns a set view of the mappings contained in this map.
 boolean equals sample code for java.util.AbstractMap.equals(java.lang.Object) definition code for java.util.AbstractMap.equals(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  o)
          Compares the specified object with this map for equality.
 V get sample code for java.util.AbstractMap.get(java.lang.Object) definition code for java.util.AbstractMap.get(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  key)
          Returns the value to which this map maps the specified key.
 int hashCode sample code for java.util.AbstractMap.hashCode() definition code for java.util.AbstractMap.hashCode() ()
          Returns the hash code value for this map.
 boolean isEmpty sample code for java.util.AbstractMap.isEmpty() definition code for java.util.AbstractMap.isEmpty() ()
          Returns true if this map contains no key-value mappings.
 Set sample code for java.util.Set definition code for java.util.Set <K> keySet sample code for java.util.AbstractMap.keySet() definition code for java.util.AbstractMap.keySet() ()
          Returns a Set view of the keys contained in this map.
 V put sample code for java.util.AbstractMap.put(K, V) definition code for java.util.AbstractMap.put(K, V) (K key, V value)
          Associates the specified value with the specified key in this map (optional operation).
 void putAll sample code for java.util.AbstractMap.putAll(java.util.Map) definition code for java.util.AbstractMap.putAll(java.util.Map) (Map sample code for java.util.Map definition code for java.util.Map <? extends K,? extends V> t)
          Copies all of the mappings from the specified map to this map (optional operation).
 V remove sample code for java.util.AbstractMap.remove(java.lang.Object) definition code for java.util.AbstractMap.remove(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  key)
          Removes the mapping for this key from this map if present (optional operation).
 int size sample code for java.util.AbstractMap.size() definition code for java.util.AbstractMap.size() ()
          Returns the number of key-value mappings in this map.
 String sample code for java.lang.String definition code for java.lang.String toString sample code for java.util.AbstractMap.toString() definition code for java.util.AbstractMap.toString() ()
          Returns a string representation of this map.
 Collection sample code for java.util.Collection definition code for java.util.Collection <V> values sample code for java.util.AbstractMap.values() definition code for java.util.AbstractMap.values() ()
          Returns a collection view of the values contained in this map.
 
Methods inherited from class java.lang.Object sample code for java.lang.Object definition code for java.lang.Object
finalize sample code for java.lang.Object.finalize() definition code for java.lang.Object.finalize() , getClass sample code for java.lang.Object.getClass() definition code for java.lang.Object.getClass() , notify sample code for java.lang.Object.notify() definition code for java.lang.Object.notify() , notifyAll sample code for java.lang.Object.notifyAll() definition code for java.lang.Object.notifyAll() , wait sample code for java.lang.Object.wait() definition code for java.lang.Object.wait() , wait sample code for java.lang.Object.wait(long) definition code for java.lang.Object.wait(long) , wait sample code for java.lang.Object.wait(long, int) definition code for java.lang.Object.wait(long, int)
 

Constructor Detail

AbstractMap sample code for java.util.AbstractMap() definition code for java.util.AbstractMap()

protected AbstractMap()
Sole constructor. (For invocation by subclass constructors, typically implicit.)

Method Detail

size sample code for java.util.AbstractMap.size() definition code for java.util.AbstractMap.size()

public int size()
Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

This implementation returns entrySet().size().

Specified by:
size sample code for java.util.Map.size() definition code for java.util.Map.size() in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Returns:
the number of key-value mappings in this map.

isEmpty sample code for java.util.AbstractMap.isEmpty() definition code for java.util.AbstractMap.isEmpty()

public boolean isEmpty()
Returns true if this map contains no key-value mappings.

This implementation returns size() == 0.

Specified by:
isEmpty sample code for java.util.Map.isEmpty() definition code for java.util.Map.isEmpty() in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Returns:
true if this map contains no key-value mappings.

containsValue sample code for java.util.AbstractMap.containsValue(java.lang.Object) definition code for java.util.AbstractMap.containsValue(java.lang.Object)

public boolean containsValue(Object sample code for java.lang.Object definition code for java.lang.Object  value)
Returns true if this map maps one or more keys to this value. More formally, returns true if and only if this map contains at least one mapping to a value v such that (value==null ? v==null : value.equals(v)). This operation will probably require time linear in the map size for most implementations of map.

This implementation iterates over entrySet() searching for an entry with the specified value. If such an entry is found, true is returned. If the iteration terminates without finding such an entry, false is returned. Note that this implementation requires linear time in the size of the map.

Specified by:
containsValue sample code for java.util.Map.containsValue(java.lang.Object) definition code for java.util.Map.containsValue(java.lang.Object) in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Parameters:
value - value whose presence in this map is to be tested.
Returns:
true if this map maps one or more keys to this value.

containsKey sample code for java.util.AbstractMap.containsKey(java.lang.Object) definition code for java.util.AbstractMap.containsKey(java.lang.Object)

public boolean containsKey(Object sample code for java.lang.Object definition code for java.lang.Object  key)
Returns true if this map contains a mapping for the specified key.

This implementation iterates over entrySet() searching for an entry with the specified key. If such an entry is found, true is returned. If the iteration terminates without finding such an entry, false is returned. Note that this implementation requires linear time in the size of the map; many implementations will override this method.

Specified by:
containsKey sample code for java.util.Map.containsKey(java.lang.Object) definition code for java.util.Map.containsKey(java.lang.Object) in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Parameters:
key - key whose presence in this map is to be tested.
Returns:
true if this map contains a mapping for the specified key.
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the key is null and this map does not permit null keys.

get sample code for java.util.AbstractMap.get(java.lang.Object) definition code for java.util.AbstractMap.get(java.lang.Object)

public V get(Object sample code for java.lang.Object definition code for java.lang.Object  key)
Returns the value to which this map maps the specified key. Returns null if the map contains no mapping for this key. A return value of null does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.

This implementation iterates over entrySet() searching for an entry with the specified key. If such an entry is found, the entry's value is returned. If the iteration terminates without finding such an entry, null is returned. Note that this implementation requires linear time in the size of the map; many implementations will override this method.

Specified by:
get sample code for java.util.Map.get(java.lang.Object) definition code for java.util.Map.get(java.lang.Object) in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Parameters:
key - key whose associated value is to be returned.
Returns:
the value to which this map maps the specified key.
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the key is null and this map does not permit null keys.
See Also:
containsKey(Object) sample code for java.util.AbstractMap.containsKey(java.lang.Object) definition code for java.util.AbstractMap.containsKey(java.lang.Object)

put sample code for java.util.AbstractMap.put(K, V) definition code for java.util.AbstractMap.put(K, V)

public V put(K key,
             V value)
Associates the specified value with the specified key in this map (optional operation). If the map previously contained a mapping for this key, the old value is replaced.

This implementation always throws an UnsupportedOperationException.

Specified by:
put sample code for java.util.Map.put(K, V) definition code for java.util.Map.put(K, V) in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Parameters:
key - key with which the specified value is to be associated.
value - value to be associated with the specified key.
Returns:
previous value associated with specified key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with the specified key, if the implementation supports null values.)
Throws:
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if the put operation is not supported by this map.
ClassCastException sample code for java.lang.ClassCastException definition code for java.lang.ClassCastException - if the class of the specified key or value prevents it from being stored in this map.
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - if some aspect of this key or value * prevents it from being stored in this map.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if this map does not permit null keys or values, and the specified key or value is null.

remove sample code for java.util.AbstractMap.remove(java.lang.Object) definition code for java.util.AbstractMap.remove(java.lang.Object)

public V remove(Object sample code for java.lang.Object definition code for java.lang.Object  key)
Removes the mapping for this key from this map if present (optional operation).

This implementation iterates over entrySet() searching for an entry with the specified key. If such an entry is found, its value is obtained with its getValue operation, the entry is removed from the Collection (and the backing map) with the iterator's remove operation, and the saved value is returned. If the iteration terminates without finding such an entry, null is returned. Note that this implementation requires linear time in the size of the map; many implementations will override this method.

Note that this implementation throws an UnsupportedOperationException if the entrySet iterator does not support the remove method and this map contains a mapping for the specified key.

Specified by:
remove sample code for java.util.Map.remove(java.lang.Object) definition code for java.util.Map.remove(java.lang.Object) in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Parameters:
key - key whose mapping is to be removed from the map.
Returns:
previous value associated with specified key, or null if there was no entry for key. (A null return can also indicate that the map previously associated null with the specified key, if the implementation supports null values.)
Throws:
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if the remove operation is not supported by this map.

putAll sample code for java.util.AbstractMap.putAll(java.util.Map<? extends K, ? extends V>) definition code for java.util.AbstractMap.putAll(java.util.Map<? extends K, ? extends V>)

public void putAll(Map sample code for java.util.Map definition code for java.util.Map <? extends K,? extends V> t)
Copies all of the mappings from the specified map to this map (optional operation). These mappings will replace any mappings that this map had for any of the keys currently in the specified map.

This implementation iterates over the specified map's entrySet() collection, and calls this map's put operation once for each entry returned by the iteration.

Note that this implementation throws an UnsupportedOperationException if this map does not support the put operation and the specified map is nonempty.

Specified by:
putAll sample code for java.util.Map.putAll(java.util.Map) definition code for java.util.Map.putAll(java.util.Map) in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Parameters:
t - mappings to be stored in this map.
Throws:
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if the putAll operation is not supported by this map.
ClassCastException sample code for java.lang.ClassCastException definition code for java.lang.ClassCastException - if the class of a key or value in the specified map prevents it from being stored in this map.
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - if some aspect of a key or value in the specified map prevents it from being stored in this map.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified map is null, or if this map does not permit null keys or values, and the specified map contains null keys or values.

clear sample code for java.util.AbstractMap.clear() definition code for java.util.AbstractMap.clear()

public void clear()
Removes all mappings from this map (optional operation).

This implementation calls entrySet().clear(). Note that this implementation throws an UnsupportedOperationException if the entrySet does not support the clear operation.

Specified by:
clear sample code for java.util.Map.clear() definition code for java.util.Map.clear() in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Throws:
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - clear is not supported by this map.

keySet sample code for java.util.AbstractMap.keySet() definition code for java.util.AbstractMap.keySet()

public Set sample code for java.util.Set definition code for java.util.Set <K> keySet()
Returns a Set view of the keys contained in this map. The Set is backed by the map, so changes to the map are reflected in the Set, and vice-versa. (If the map is modified while an iteration over the Set is in progress, the results of the iteration are undefined.) The Set supports element removal, which removes the corresponding entry from the map, via the Iterator.remove, Set.remove, removeAll retainAll, and clear operations. It does not support the add or addAll operations.

This implementation returns a Set that subclasses AbstractSet. The subclass's iterator method returns a "wrapper object" over this map's entrySet() iterator. The size method delegates to this map's size method and the contains method delegates to this map's containsKey method.

The Set is created the first time this method is called, and returned in response to all subsequent calls. No synchronization is performed, so there is a slight chance that multiple calls to this method will not all return the same Set.

Specified by:
keySet sample code for java.util.Map.keySet() definition code for java.util.Map.keySet() in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Returns:
a Set view of the keys contained in this map.

values sample code for java.util.AbstractMap.values() definition code for java.util.AbstractMap.values()

public Collection sample code for java.util.Collection definition code for java.util.Collection <V> values()
Returns a collection view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. (If the map is modified while an iteration over the collection is in progress, the results of the iteration are undefined.) The collection supports element removal, which removes the corresponding entry from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

This implementation returns a collection that subclasses abstract collection. The subclass's iterator method returns a "wrapper object" over this map's entrySet() iterator. The size method delegates to this map's size method and the contains method delegates to this map's containsValue method.

The collection is created the first time this method is called, and returned in response to all subsequent calls. No synchronization is performed, so there is a slight chance that multiple calls to this method will not all return the same Collection.

Specified by:
values sample code for java.util.Map.values() definition code for java.util.Map.values() in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Returns:
a collection view of the values contained in this map.

entrySet sample code for java.util.AbstractMap.entrySet() definition code for java.util.AbstractMap.entrySet()

public abstract Set sample code for java.util.Set definition code for java.util.Set <Map.Entry sample code for java.util.Map.Entry definition code for java.util.Map.Entry <K,V>> entrySet()
Returns a set view of the mappings contained in this map. Each element in this set is a Map.Entry. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. (If the map is modified while an iteration over the set is in progress, the results of the iteration are undefined.) The set supports element removal, which removes the corresponding entry from the map, via the Iterator.remove, Set.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

Specified by:
entrySet sample code for java.util.Map.entrySet() definition code for java.util.Map.entrySet() in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Returns:
a set view of the mappings contained in this map.

equals sample code for java.util.AbstractMap.equals(java.lang.Object) definition code for java.util.AbstractMap.equals(java.lang.Object)

public boolean equals(Object sample code for java.lang.Object definition code for java.lang.Object  o)
Compares the specified object with this map for equality. Returns true if the given object is also a map and the two maps represent the same mappings. More formally, two maps t1 and t2 represent the same mappings if t1.keySet().equals(t2.keySet()) and for every key k in t1.keySet(), (t1.get(k)==null ? t2.get(k)==null : t1.get(k).equals(t2.get(k))) . This ensures that the equals method works properly across different implementations of the map interface.

This implementation first checks if the specified object is this map; if so it returns true. Then, it checks if the specified object is a map whose size is identical to the size of this set; if not, it returns false. If so, it iterates over this map's entrySet collection, and checks that the specified map contains each mapping that this map contains. If the specified map fails to contain such a mapping, false is returned. If the iteration completes, true is returned.

Specified by:
equals sample code for java.util.Map.equals(java.lang.Object) definition code for java.util.Map.equals(java.lang.Object) in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Overrides:
equals sample code for java.lang.Object.equals(java.lang.Object) definition code for java.lang.Object.equals(java.lang.Object) in class Object sample code for java.lang.Object definition code for java.lang.Object
Parameters:
o - object to be compared for equality with this map.
Returns:
true if the specified object is equal to this map.
See Also:
Object.hashCode() sample code for java.lang.Object.hashCode() definition code for java.lang.Object.hashCode() , Hashtable sample code for java.util.Hashtable definition code for java.util.Hashtable

hashCode sample code for java.util.AbstractMap.hashCode() definition code for java.util.AbstractMap.hashCode()

public int hashCode()
Returns the hash code value for this map. The hash code of a map is defined to be the sum of the hash codes of each entry in the map's entrySet() view. This ensures that t1.equals(t2) implies that t1.hashCode()==t2.hashCode() for any two maps t1 and t2, as required by the general contract of Object.hashCode.

This implementation iterates over entrySet(), calling hashCode on each element (entry) in the Collection, and adding up the results.

Specified by:
hashCode sample code for java.util.Map.hashCode() definition code for java.util.Map.hashCode() in interface Map sample code for java.util.Map definition code for java.util.Map <K,V>
Overrides:
hashCode sample code for java.lang.Object.hashCode() definition code for java.lang.Object.hashCode() in class Object sample code for java.lang.Object definition code for java.lang.Object
Returns:
the hash code value for this map.
See Also:
Map.Entry.hashCode() sample code for java.util.Map.Entry.hashCode() definition code for java.util.Map.Entry.hashCode() , Object.hashCode() sample code for java.lang.Object.hashCode() definition code for java.lang.Object.hashCode() , Object.equals(Object) sample code for java.lang.Object.equals(java.lang.Object) definition code for java.lang.Object.equals(java.lang.Object) , Set.equals(Object) sample code for java.util.Set.equals(java.lang.Object) definition code for java.util.Set.equals(java.lang.Object)

toString sample code for java.util.AbstractMap.toString() definition code for java.util.AbstractMap.toString()

public String sample code for java.lang.String definition code for java.lang.String  toString()
Returns a string representation of this map. The string representation consists of a list of key-value mappings in the order returned by the map's entrySet view's iterator, enclosed in braces ("{}"). Adjacent mappings are separated by the characters ", " (comma and space). Each key-value mapping is rendered as the key followed by an equals sign ("=") followed by the associated value. Keys and values are converted to strings as by String.valueOf(Object).

This implementation creates an empty string buffer, appends a left brace, and iterates over the map's entrySet view, appending the string representation of each map.entry in turn. After appending each entry except the last, the string ", " is appended. Finally a right brace is appended. A string is obtained from the stringbuffer, and returned.

Overrides:
toString sample code for java.lang.Object.toString() definition code for java.lang.Object.toString() in class Object sample code for java.lang.Object definition code for java.lang.Object
Returns:
a String representation of this map.

clone sample code for java.util.AbstractMap.clone() definition code for java.util.AbstractMap.clone()

protected Object sample code for java.lang.Object definition code for java.lang.Object  clone()
                throws CloneNotSupportedException sample code for java.lang.CloneNotSupportedException definition code for java.lang.CloneNotSupportedException 
Returns a shallow copy of this AbstractMap instance: the keys and values themselves are not cloned.

Overrides:
clone sample code for java.lang.Object.clone() definition code for java.lang.Object.clone() in class Object sample code for java.lang.Object definition code for java.lang.Object
Returns:
a shallow copy of this map.
Throws:
CloneNotSupportedException sample code for java.lang.CloneNotSupportedException definition code for java.lang.CloneNotSupportedException - if the object's class does not support the Cloneable interface. Subclasses that override the clone method can also throw this exception to indicate that an instance cannot be cloned.
See Also:
Cloneable sample code for java.lang.Cloneable definition code for java.lang.Cloneable