EnumMap
here we check the EnumMap class,
public class EnumMap<K extends Enum<K>, V> extends AbstractMap<K, V>
implements java.io.Serializable, Cloneable
{
/**
* The <tt>Class</tt> object for the enum type of all the keys of this map.
*
* @serial
*/
private final Class<K> keyType;
/**
* All of the values comprising K. (Cached for performance.)
*/
private transient K[] keyUniverse;
/**
* Array representation of this map. The ith element is the value
* to which universe[i] is currently mapped, or null if it isn't
* mapped to anything, or NULL if it's mapped to null.
*/
private transient Object[] vals;
/**
* The number of mappings in this map.
*/
private transient int size = 0;
/**
* Distinguished non-null value for representing null values.
*/
private static final Object NULL = new Object() {
public int hashCode() {
return 0;
}
public String toString() {
return "java.util.EnumMap.NULL";
}
};
private Object maskNull(Object value) {
return (value == null ? NULL : value);
}
private V unmaskNull(Object value) {
return (V) (value == NULL ? null : value);
}
private static final Enum[] ZERO_LENGTH_ENUM_ARRAY = new Enum[0];
/**
* Creates an empty enum map with the specified key type.
*
* @param keyType the class object of the key type for this enum map
* @throws NullPointerException if <tt>keyType</tt> is null
*
* Saturday this is strange constructor of EnumMap, it seems like here the
* EnumMap should remember thsi key class type, so just put this as the argumet
* of the constructor, so...
*/
public EnumMap(Class<K> keyType) {
this.keyType = keyType;
keyUniverse = getKeyUniverse(keyType);
vals = new Object[keyUniverse.length];
}
/**
* Creates an enum map with the same key type as the specified enum
* map, initially containing the same mappings (if any).
*
* @param m the enum map from which to initialize this enum map
* @throws NullPointerException if <tt>m</tt> 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 initialized from the specified map. If the
* specified map is an <tt>EnumMap</tt> instance, this constructor behaves
* identically to {@link #EnumMap(EnumMap)}. Otherwise, the specified map
* must contain at least one mapping (in order to determine the new
* enum map's key type).
*
* @param m the map from which to initialize this enum map
* @throws IllegalArgumentException if <tt>m</tt> is not an
* <tt>EnumMap</tt> instance and contains no mappings
* @throws NullPointerException if <tt>m</tt> 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);
}
}
// Query Operations
/**
* Returns the number of key-value mappings in this map.
*
* @return the number of key-value mappings in this map
*/
public int size() {
return size;
}
/**
* Returns <tt>true</tt> if this map maps one or more keys to the
* specified value.
*
* @param value the value whose presence in this map is to be tested
* @return <tt>true</tt> if this map maps one or more keys to this value
*/
public boolean containsValue(Object value) {
value = maskNull(value);
for (Object val : vals)
if (value.equals(val))
return true;
return false;
}
/**
* Returns <tt>true</tt> if this map contains a mapping for the specified
* key.
*
* @param key the key whose presence in this map is to be tested
* @return <tt>true</tt> if this map contains a mapping for the specified
* key
*/
public boolean containsKey(Object key) {
return isValidKey(key) && vals[((Enum)key).ordinal()] != null;
}
private boolean containsMapping(Object key, Object value) {
return isValidKey(key) &&
maskNull(value).equals(vals[((Enum)key).ordinal()]);
}
/**
* Returns the value to which the specified key is mapped,
* or {@code null} if this map contains no mapping for the key.
*
* <p>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.)
*
* <p>A return value of {@code null} does not <i>necessarily</i>
* 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 {@link #containsKey containsKey} operation may be used to
* distinguish these two cases.
*/
public V get(Object key) {
return (isValidKey(key) ?
unmaskNull(vals[((Enum)key).ordinal()]) : null);
}
// Modification Operations
/**
* 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.
*
* @param key the key with which the specified value is to be associated
* @param value the value to be associated with the specified key
*
* @return the previous value associated with specified key, or
* <tt>null</tt> if there was no mapping for key. (A <tt>null</tt>
* return can also indicate that the map previously associated
* <tt>null</tt> with the specified key.)
* @throws NullPointerException if the specified key is null
*/
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);
}
/**
* Removes the mapping for this key from this map if present.
*
* @param key the key whose mapping is to be removed from the map
* @return the previous value associated with specified key, or
* <tt>null</tt> if there was no entry for key. (A <tt>null</tt>
* return can also indicate that the map previously associated
* <tt>null</tt> with the specified key.)
*/
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);
}
private boolean removeMapping(Object key, Object value) {
if (!isValidKey(key))
return false;
int index = ((Enum)key).ordinal();
if (maskNull(value).equals(vals[index])) {
vals[index] = null;
size--;
return true;
}
return false;
}
/**
* Returns true if key is of the proper type to be a key in this
* enum map.
*/
private boolean isValidKey(Object key) {
if (key == null)
return false;
// Cheaper than instanceof Enum followed by getDeclaringClass
Class keyClass = key.getClass();
return keyClass == keyType || keyClass.getSuperclass() == keyType;
}
// Bulk Operations
/**
* 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.
*
* @param m the mappings to be stored in this map
* @throws NullPointerException the specified map is null, or if
* one or more keys in the specified map are null
*/
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);
}
}
/**
* Removes all mappings from this map.
*/
public void clear() {
Arrays.fill(vals, null);
size = 0;
}
// Views
/**
* This field is initialized to contain an instance of the entry set
* view the first time this view is requested. The view is stateless,
* so there's no reason to create more than one.
*/
private transient Set<Map.Entry<K,V>> entrySet = null;
/**
* Returns a {@link Set} view of the keys contained in this map.
* The returned set obeys the general contract outlined in
* {@link Map#keySet()}. The set's iterator will return the keys
* in their natural order (the order in which the enum constants
* are declared).
*
* @return a set view of the keys contained in this enum map
*/
public Set<K> keySet() {
Set<K> ks = keySet;
if (ks != null)
return ks;
else
return keySet = new KeySet();
}
private class KeySet extends AbstractSet<K> {
public Iterator<K> iterator() {
return new KeyIterator();
}
public int size() {
return size;
}
public boolean contains(Object o) {
return containsKey(o);
}
public boolean remove(Object o) {
int oldSize = size;
EnumMap.this.remove(o);
return size != oldSize;
}
public void clear() {
EnumMap.this.clear();
}
}
/**
* Returns a {@link Collection} view of the values contained in this map.
* The returned collection obeys the general contract outlined in
* {@link 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).
*
* @return a collection view of the values contained in this map
*/
public Collection<V> values() {
Collection<V> vs = values;
if (vs != null)
return vs;
else
return values = new Values();
}
private class Values extends AbstractCollection<V> {
public Iterator<V> iterator() {
return new ValueIterator();
}
public int size() {
return size;
}
public boolean contains(Object o) {
return containsValue(o);
}
public boolean remove(Object o) {
o = maskNull(o);
for (int i = 0; i < vals.length; i++) {
if (o.equals(vals[i])) {
vals[i] = null;
size--;
return true;
}
}
return false;
}
public void clear() {
EnumMap.this.clear();
}
}
/**
* Returns a {@link Set} view of the mappings contained in this map.
* The returned set obeys the general contract outlined in
* {@link 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).
*
* @return a set view of the mappings contained in this enum map
*/
public Set<Map.Entry<K,V>> entrySet() {
Set<Map.Entry<K,V>> es = entrySet;
if (es != null)
return es;
else
return entrySet = new EntrySet();
}
private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
public Iterator<Map.Entry<K,V>> iterator() {
return new EntryIterator();
}
public boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry entry = (Map.Entry)o;
return containsMapping(entry.getKey(), entry.getValue());
}
public boolean remove(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry entry = (Map.Entry)o;
return removeMapping(entry.getKey(), entry.getValue());
}
public int size() {
return size;
}
public void clear() {
EnumMap.this.clear();
}
public Object[] toArray() {
return fillEntryArray(new Object[size]);
}
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
int size = size();
if (a.length < size)
a = (T[])java.lang.reflect.Array
.newInstance(a.getClass().getComponentType(), size);
if (a.length > size)
a[size] = null;
return (T[]) fillEntryArray(a);
}
private Object[] fillEntryArray(Object[] a) {
int j = 0;
for (int i = 0; i < vals.length; i++)
if (vals[i] != null)
a[j++] = new AbstractMap.SimpleEntry<>(
keyUniverse[i], unmaskNull(vals[i]));
return a;
}
}
private abstract class EnumMapIterator<T> implements Iterator<T> {
// Lower bound on index of next element to return
int index = 0;
// Index of last returned element, or -1 if none
int lastReturnedIndex = -1;
public boolean hasNext() {
while (index < vals.length && vals[index] == null)
index++;
return index != vals.length;
}
public void remove() {
checkLastReturnedIndex();
if (vals[lastReturnedIndex] != null) {
vals[lastReturnedIndex] = null;
size--;
}
lastReturnedIndex = -1;
}
private void checkLastReturnedIndex() {
if (lastReturnedIndex < 0)
throw new IllegalStateException();
}
}
private class KeyIterator extends EnumMapIterator<K> {
public K next() {
if (!hasNext())
throw new NoSuchElementException();
lastReturnedIndex = index++;
return keyUniverse[lastReturnedIndex];
}
}
private class ValueIterator extends EnumMapIterator<V> {
public V next() {
if (!hasNext())
throw new NoSuchElementException();
lastReturnedIndex = index++;
return unmaskNull(vals[lastReturnedIndex]);
}
}
private class EntryIterator extends EnumMapIterator<Map.Entry<K,V>> {
private Entry lastReturnedEntry = null;
public Map.Entry<K,V> next() {
if (!hasNext())
throw new NoSuchElementException();
lastReturnedEntry = new Entry(index++);
return lastReturnedEntry;
}
public void remove() {
lastReturnedIndex =
((null == lastReturnedEntry) ? -1 : lastReturnedEntry.index);
super.remove();
lastReturnedEntry.index = lastReturnedIndex;
lastReturnedEntry = null;
}
private class Entry implements Map.Entry<K,V> {
private int index;
private Entry(int index) {
this.index = index;
}
public K getKey() {
checkIndexForEntryUse();
return keyUniverse[index];
}
public V getValue() {
checkIndexForEntryUse();
return unmaskNull(vals[index]);
}
public V setValue(V value) {
checkIndexForEntryUse();
V oldValue = unmaskNull(vals[index]);
vals[index] = maskNull(value);
return oldValue;
}
public boolean equals(Object o) {
if (index < 0)
return o == this;
if (!(o instanceof Map.Entry))
return false;
Map.Entry e = (Map.Entry)o;
V ourValue = unmaskNull(vals[index]);
Object hisValue = e.getValue();
return (e.getKey() == keyUniverse[index] &&
(ourValue == hisValue ||
(ourValue != null && ourValue.equals(hisValue))));
}
public int hashCode() {
if (index < 0)
return super.hashCode();
return entryHashCode(index);
}
public String toString() {
if (index < 0)
return super.toString();
return keyUniverse[index] + "="
+ unmaskNull(vals[index]);
}
private void checkIndexForEntryUse() {
if (index < 0)
throw new IllegalStateException("Entry was removed");
}
}
}
// Comparison and hashing
/**
* Compares the specified object with this map for equality. Returns
* <tt>true</tt> if the given object is also a map and the two maps
* represent the same mappings, as specified in the {@link
* Map#equals(Object)} contract.
*
* @param o the object to be compared for equality with this map
* @return <tt>true</tt> if the specified object is equal to this map
*/
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;
}
private boolean equals(EnumMap em) {
if (em.keyType != keyType)
return size == 0 && em.size == 0;
// Key types match, compare each value
for (int i = 0; i < keyUniverse.length; i++) {
Object ourValue = vals[i];
Object hisValue = em.vals[i];
if (hisValue != ourValue &&
(hisValue == null || !hisValue.equals(ourValue)))
return false;
}
return true;
}
/**
* 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 int hashCode() {
int h = 0;
for (int i = 0; i < keyUniverse.length; i++) {
if (null != vals[i]) {
h += entryHashCode(i);
}
}
return h;
}
private int entryHashCode(int index) {
return (keyUniverse[index].hashCode() ^ vals[index].hashCode());
}
/**
* Returns a shallow copy of this enum map. (The values themselves
* are not cloned.
*
* @return a shallow copy of this enum 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();
result.entrySet = null;
return result;
}
/**
* Throws an exception if e is not of the correct type for this enum set.
*/
private void typeCheck(K key) {
Class keyClass = key.getClass();
if (keyClass != keyType && keyClass.getSuperclass() != keyType)
throw new ClassCastException(keyClass + " != " + keyType);
}
/**
* Returns all of the values comprising K.
* The result is uncloned, cached, and shared by all callers.
*/
private static <K extends Enum<K>> K[] getKeyUniverse(Class<K> keyType) {
return SharedSecrets.getJavaLangAccess()
.getEnumConstantsShared(keyType);
}
private static final long serialVersionUID = 458661240069192865L;
/**
* Save the state of the <tt>EnumMap</tt> instance to a stream (i.e.,
* serialize it).
*
* @serialData The <i>size</i> of the enum map (the number of key-value
* mappings) is emitted (int), followed by the key (Object)
* and value (Object) for each key-value mapping represented
* by the enum map.
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException
{
// Write out the key type and any hidden stuff
s.defaultWriteObject();
// Write out size (number of Mappings)
s.writeInt(size);
// Write out keys and values (alternating)
int entriesToBeWritten = size;
for (int i = 0; entriesToBeWritten > 0; i++) {
if (null != vals[i]) {
s.writeObject(keyUniverse[i]);
s.writeObject(unmaskNull(vals[i]));
entriesToBeWritten--;
}
}
}
/**
* Reconstitute the <tt>EnumMap</tt> instance from a stream (i.e.,
* deserialize it).
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException
{
// Read in the key type and any hidden stuff
s.defaultReadObject();
keyUniverse = getKeyUniverse(keyType);
vals = new Object[keyUniverse.length];
// Read in size (number of Mappings)
int size = s.readInt();
// Read the keys and values, and put the mappings in the HashMap
for (int i = 0; i < size; i++) {
K key = (K) s.readObject();
V value = (V) s.readObject();
put(key, value);
}
}
}