AbstractMappublic abstract class AbstractMap extends Object implements Map| 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 method 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. |
| Fields Summary |
|---|
| volatile transient Set | keySetEach of these fields are initialized to contain an instance of the
appropriate view the first time this view is requested. The views are
stateless, so there's no reason to create more than one of each. | | volatile transient Collection | values |
| Constructors Summary |
|---|
protected AbstractMap()Sole constructor. (For invocation by subclass constructors, typically
implicit.)
|
| Methods Summary |
|---|
| public void | clear(){@inheritDoc}
This implementation calls entrySet().clear().
Note that this implementation throws an
UnsupportedOperationException if the entrySet
does not support the clear operation.
entrySet().clear();
| | protected java.lang.Object | clone()Returns a shallow copy of this AbstractMap instance: the keys
and values themselves are not cloned.
AbstractMap<K,V> result = (AbstractMap<K,V>)super.clone();
result.keySet = null;
result.values = null;
return result;
| | public boolean | containsKey(java.lang.Object key){@inheritDoc}
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.
Iterator<Map.Entry<K,V>> i = entrySet().iterator();
if (key==null) {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (e.getKey()==null)
return true;
}
} else {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (key.equals(e.getKey()))
return true;
}
}
return false;
| | public boolean | containsValue(java.lang.Object value){@inheritDoc}
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.
Iterator<Entry<K,V>> i = entrySet().iterator();
if (value==null) {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (e.getValue()==null)
return true;
}
} else {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (value.equals(e.getValue()))
return true;
}
}
return false;
| | public abstract java.util.Set | entrySet()
| | private static boolean | eq(java.lang.Object o1, java.lang.Object o2)Utility method for SimpleEntry and SimpleImmutableEntry.
Test for equality, checking for nulls.
return o1 == null ? o2 == null : o1.equals(o2);
| | public boolean | equals(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 m1 and
m2 represent the same mappings if
m1.entrySet().equals(m2.entrySet()). 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 map; 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.
if (o == this)
return true;
if (!(o instanceof Map))
return false;
Map<K,V> m = (Map<K,V>) o;
if (m.size() != size())
return false;
try {
Iterator<Entry<K,V>> i = entrySet().iterator();
while (i.hasNext()) {
Entry<K,V> e = i.next();
K key = e.getKey();
V value = e.getValue();
if (value == null) {
if (!(m.get(key)==null && m.containsKey(key)))
return false;
} else {
if (!value.equals(m.get(key)))
return false;
}
}
} catch (ClassCastException unused) {
return false;
} catch (NullPointerException unused) {
return false;
}
return true;
| | public V | get(java.lang.Object key){@inheritDoc}
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.
Iterator<Entry<K,V>> i = entrySet().iterator();
if (key==null) {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (e.getKey()==null)
return e.getValue();
}
} else {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (key.equals(e.getKey()))
return e.getValue();
}
}
return null;
| | 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 m1.equals(m2)
implies that m1.hashCode()==m2.hashCode() for any two maps
m1 and m2, as required by the general contract of
{@link Object#hashCode}.
This implementation iterates over entrySet(), calling
{@link Map.Entry#hashCode hashCode()} on each element (entry) in the
set, and adding up the results.
int h = 0;
Iterator<Entry<K,V>> i = entrySet().iterator();
while (i.hasNext())
h += i.next().hashCode();
return h;
| | public boolean | isEmpty(){@inheritDoc}
This implementation returns size() == 0.
return size() == 0;
| | public java.util.Set | keySet(){@inheritDoc}
This implementation returns a set that subclasses {@link 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.
if (keySet == null) {
keySet = new AbstractSet<K>() {
public Iterator<K> iterator() {
return new Iterator<K>() {
private Iterator<Entry<K,V>> i = entrySet().iterator();
public boolean hasNext() {
return i.hasNext();
}
public K next() {
return i.next().getKey();
}
public void remove() {
i.remove();
}
};
}
public int size() {
return AbstractMap.this.size();
}
public boolean contains(Object k) {
return AbstractMap.this.containsKey(k);
}
};
}
return keySet;
| | public V | put(K key, V value){@inheritDoc}
This implementation always throws an
UnsupportedOperationException.
throw new UnsupportedOperationException();
| | public void | putAll(java.util.Map m){@inheritDoc}
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.
for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
put(e.getKey(), e.getValue());
| | public V | remove(java.lang.Object key){@inheritDoc}
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.
Iterator<Entry<K,V>> i = entrySet().iterator();
Entry<K,V> correctEntry = null;
if (key==null) {
while (correctEntry==null && i.hasNext()) {
Entry<K,V> e = i.next();
if (e.getKey()==null)
correctEntry = e;
}
} else {
while (correctEntry==null && i.hasNext()) {
Entry<K,V> e = i.next();
if (key.equals(e.getKey()))
correctEntry = e;
}
}
V oldValue = null;
if (correctEntry !=null) {
oldValue = correctEntry.getValue();
i.remove();
}
return oldValue;
| | public int | size(){@inheritDoc}
This implementation returns entrySet().size().
return entrySet().size();
| | public 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
{@link String#valueOf(Object)}.
Iterator<Entry<K,V>> i = entrySet().iterator();
if (! i.hasNext())
return "{}";
StringBuilder sb = new StringBuilder();
sb.append('{");
for (;;) {
Entry<K,V> e = i.next();
K key = e.getKey();
V value = e.getValue();
sb.append(key == this ? "(this Map)" : key);
sb.append('=");
sb.append(value == this ? "(this Map)" : value);
if (! i.hasNext())
return sb.append('}").toString();
sb.append(", ");
}
| | public java.util.Collection | values(){@inheritDoc}
This implementation returns a collection that subclasses {@link
AbstractCollection}. 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.
if (values == null) {
values = new AbstractCollection<V>() {
public Iterator<V> iterator() {
return new Iterator<V>() {
private Iterator<Entry<K,V>> i = entrySet().iterator();
public boolean hasNext() {
return i.hasNext();
}
public V next() {
return i.next().getValue();
}
public void remove() {
i.remove();
}
};
}
public int size() {
return AbstractMap.this.size();
}
public boolean contains(Object v) {
return AbstractMap.this.containsValue(v);
}
};
}
return values;
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