java.util
public class: EnumMap [javadoc |
source]
java.lang.Object
java.util.AbstractMap<K, V>
java.util.EnumMap
All Implemented Interfaces:
Cloneable, java$io$Serializable, Map
A specialized
Map implementation for use with enum type keys. All
of the keys in an enum map must come from a single enum type that is
specified, explicitly or implicitly, when the map is created. Enum maps
are represented internally as arrays. This representation is extremely
compact and efficient.
Enum maps are maintained in the natural order of their keys
(the order in which the enum constants are declared). This is reflected
in the iterators returned by the collections views (#keySet() ,
#entrySet() , and #values() ).
Iterators returned by the collection views are weakly consistent:
they will never throw ConcurrentModificationException and they may
or may not show the effects of any modifications to the map that occur while
the iteration is in progress.
Null keys are not permitted. Attempts to insert a null key will
throw NullPointerException . Attempts to test for the
presence of a null key or to remove one will, however, function properly.
Null values are permitted.
Like most collection implementations EnumMap is not
synchronized. If multiple threads access an enum map concurrently, and at
least one of the threads modifies the map, it should be synchronized
externally. This is typically accomplished by synchronizing on some
object that naturally encapsulates the enum map. If no such object exists,
the map should be "wrapped" using the Collections#synchronizedMap
method. This is best done at creation time, to prevent accidental
unsynchronized access:
Map<EnumKey, V> m
= Collections.synchronizedMap(new EnumMap<EnumKey, V>(...));
Implementation note: All basic operations execute in constant time.
They are likely (though not guaranteed) to be faster than their
HashMap counterparts.
This class is a member of the
Java Collections Framework.
Also see:
- EnumSet
- author:
Josh - Bloch
- since:
1.5 -
| Constructor: |
|---|
 public EnumMap(Class<K> keyType) {
this.keyType = keyType;
keyUniverse = getKeyUniverse(keyType);
vals = new Object[keyUniverse.length];
}
Creates an empty enum map with the specified key type. Parameters:
keyType - the class object of the key type for this enum map
NullPointerException - if keyType is null
|
public EnumMap(EnumMap<K, ? extends V> m) {
keyType = m.keyType;
keyUniverse = m.keyUniverse;
vals = m.vals.clone();
size = m.size;
} Creates an enum map with the same key type as the specified enum
map, initially containing the same mappings (if any). Parameters:
m - the enum map from which to initialize this enum map
NullPointerException - if m is null
|
public EnumMap(Map<K, ? extends V> m) {
if (m instanceof EnumMap) {
EnumMap< K, ? extends V > em = (EnumMap< K, ? extends V >) m;
keyType = em.keyType;
keyUniverse = em.keyUniverse;
vals = em.vals.clone();
size = em.size;
} else {
if (m.isEmpty())
throw new IllegalArgumentException("Specified map is empty");
keyType = m.keySet().iterator().next().getDeclaringClass();
keyUniverse = getKeyUniverse(keyType);
vals = new Object[keyUniverse.length];
putAll(m);
}
} Creates an enum map initialized from the specified map. If the
specified map is an EnumMap instance, this constructor behaves
identically to #EnumMap(EnumMap) . Otherwise, the specified map
must contain at least one mapping (in order to determine the new
enum map's key type). Parameters:
m - the map from which to initialize this enum map
IllegalArgumentException - if m is not an
EnumMap instance and contains no mappings
NullPointerException - if m is null
|
| Method from java.util.EnumMap Summary: |
|---|
|
clear, clone, containsKey, containsValue, entrySet, equals, get, hashCode, keySet, put, putAll, remove, size, values |
| Methods from java.util.AbstractMap: |
|---|
|
clear, clone, containsKey, containsValue, entrySet, equals, get, hashCode, isEmpty, keySet, put, putAll, remove, size, toString, values |
| Methods from java.lang.Object: |
|---|
|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Method from java.util.EnumMap Detail: |
|---|
public void clear() {
Arrays.fill(vals, null);
size = 0;
} Removes all mappings from this map. |
public EnumMap<K, V> clone() {
EnumMap< K, V > result = null;
try {
result = (EnumMap< K, V >) super.clone();
} catch(CloneNotSupportedException e) {
throw new AssertionError();
}
result.vals = result.vals.clone();
return result;
} Returns a shallow copy of this enum map. (The values themselves
are not cloned. |
public boolean containsKey(Object key) {
return isValidKey(key) && vals[((Enum)key).ordinal()] != null;
} Returns true if this map contains a mapping for the specified
key. |
public boolean containsValue(Object value) {
value = maskNull(value);
for (Object val : vals)
if (value.equals(val))
return true;
return false;
} Returns true if this map maps one or more keys to the
specified value. |
public Set<K, V> entrySet() {
Set< Map.Entry< K,V > > es = entrySet;
if (es != null)
return es;
else
return entrySet = new EntrySet();
} Returns a Set view of the mappings contained in this map.
The returned set obeys the general contract outlined in
Map#keySet() . The set's iterator will return the
mappings in the order their keys appear in map, which is their
natural order (the order in which the enum constants are declared). |
public boolean equals(Object o) {
if (this == o)
return true;
if (o instanceof EnumMap)
return equals((EnumMap)o);
if (!(o instanceof Map))
return false;
Map< K,V > m = (Map< K,V >)o;
if (size != m.size())
return false;
for (int i = 0; i < keyUniverse.length; i++) {
if (null != vals[i]) {
K key = keyUniverse[i];
V value = unmaskNull(vals[i]);
if (null == value) {
if (!((null == m.get(key)) && m.containsKey(key)))
return false;
} else {
if (!value.equals(m.get(key)))
return false;
}
}
}
return true;
} 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, as specified in the Map#equals(Object) contract. |
public V get(Object key) {
return (isValidKey(key) ?
unmaskNull(vals[((Enum)key).ordinal()]) : null);
} Returns the value to which the specified key is mapped,
or {@code null} if this map contains no mapping for the key.
More formally, if this map contains a mapping from a key
{@code k} to a value {@code v} such that {@code (key == k)},
then this method returns {@code v}; otherwise it returns
{@code null}. (There can be at most one such mapping.)
A return value of {@code 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 {@code null}.
The containsKey operation may be used to
distinguish these two cases. |
public int hashCode() {
int h = 0;
for (int i = 0; i < keyUniverse.length; i++) {
if (null != vals[i]) {
h += entryHashCode(i);
}
}
return h;
} 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. |
public Set<K> keySet() {
Set< K > ks = keySet;
if (ks != null)
return ks;
else
return keySet = new KeySet();
} Returns a Set view of the keys contained in this map.
The returned set obeys the general contract outlined in
Map#keySet() . The set's iterator will return the keys
in their natural order (the order in which the enum constants
are declared). |
public V put(K key,
V value) {
typeCheck(key);
int index = key.ordinal();
Object oldValue = vals[index];
vals[index] = maskNull(value);
if (oldValue == null)
size++;
return unmaskNull(oldValue);
} Associates the specified value with the specified key in this map.
If the map previously contained a mapping for this key, the old
value is replaced. |
public void putAll(Map<? extends K, ? extends V> m) {
if (m instanceof EnumMap) {
EnumMap< ? extends K, ? extends V > em =
(EnumMap< ? extends K, ? extends V >)m;
if (em.keyType != keyType) {
if (em.isEmpty())
return;
throw new ClassCastException(em.keyType + " != " + keyType);
}
for (int i = 0; i < keyUniverse.length; i++) {
Object emValue = em.vals[i];
if (emValue != null) {
if (vals[i] == null)
size++;
vals[i] = emValue;
}
}
} else {
super.putAll(m);
}
} Copies all of the mappings from the specified map to this map.
These mappings will replace any mappings that this map had for
any of the keys currently in the specified map. |
public V remove(Object key) {
if (!isValidKey(key))
return null;
int index = ((Enum)key).ordinal();
Object oldValue = vals[index];
vals[index] = null;
if (oldValue != null)
size--;
return unmaskNull(oldValue);
} Removes the mapping for this key from this map if present. |
public int size() {
return size;
} Returns the number of key-value mappings in this map. |
public Collection<V> values() {
Collection< V > vs = values;
if (vs != null)
return vs;
else
return values = new Values();
} Returns a Collection view of the values contained in this map.
The returned collection obeys the general contract outlined in
Map#values() . The collection's iterator will return the
values in the order their corresponding keys appear in map,
which is their natural order (the order in which the enum constants
are declared). |