/**
* Retrieve object hash code and applies a supplemental hash function to the result hash, which
* defends against poor quality hash functions. This is critical because HashMap uses power-of-two
* length hash tables, that otherwise encounter collisions for hashCodes that do not differ in
* lower bits. Note: Null keys always map to hash 0, thus index 0.
*/
final int hash(Object k) {
int h = 0;
if (useAltHashing) {
if (k instanceof String) {
return sun.misc.Hashing.stringHash32((String) k);
}
h = hashSeed;
}
h ^= k.hashCode();
// This function ensures that hashCodes that differ only by
// constant multiples at each bit position have a bounded
// number of collisions (approximately 8 at default load factor).
h ^= (h >>> 20) ^ (h >>> 12);
return h ^ (h >>> 7) ^ (h >>> 4);
}
/** Reconstitute the {@code HashMap} instance from a stream (i.e., deserialize it). */
private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException {
// Read in the threshold (ignored), loadfactor, and any hidden stuff
s.defaultReadObject();
if (loadFactor <= 0 || Float.isNaN(loadFactor))
throw new InvalidObjectException("Illegal load factor: " + loadFactor);
// set hashSeed (can only happen after VM boot)
Holder.UNSAFE.putIntVolatile(
this, Holder.HASHSEED_OFFSET, sun.misc.Hashing.randomHashSeed(this));
// Read in number of buckets and allocate the bucket array;
s.readInt(); // ignored
// Read number of mappings
int mappings = s.readInt();
if (mappings < 0) throw new InvalidObjectException("Illegal mappings count: " + mappings);
int initialCapacity =
(int)
Math.min(
// capacity chosen by number of mappings
// and desired load (if >= 0.25)
mappings * Math.min(1 / loadFactor, 4.0f),
// we have limits...
HashMap.MAXIMUM_CAPACITY);
int capacity = 1;
// find smallest power of two which holds all mappings
while (capacity < initialCapacity) {
capacity <<= 1;
}
table = new Entry[capacity];
threshold = (int) Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
useAltHashing = sun.misc.VM.isBooted() && (capacity >= Holder.ALTERNATIVE_HASHING_THRESHOLD);
init(); // Give subclass a chance to do its thing.
// Read the keys and values, and put the mappings in the HashMap
for (int i = 0; i < mappings; i++) {
K key = (K) s.readObject();
V value = (V) s.readObject();
putForCreate(key, value);
}
}
/**
* Hash table based implementation of the <tt>Map</tt> interface. This implementation provides all
* of the optional map operations, and permits <tt>null</tt> values and the <tt>null</tt> key. (The
* <tt>HashMap</tt> class is roughly equivalent to <tt>Hashtable</tt>, except that it is
* unsynchronized and permits nulls.) This class makes no guarantees as to the order of the map; in
* particular, it does not guarantee that the order will remain constant over time.
*
* <p>This implementation provides constant-time performance for the basic operations (<tt>get</tt>
* and <tt>put</tt>), assuming the hash function disperses the elements properly among the buckets.
* Iteration over collection views requires time proportional to the "capacity" of the
* <tt>HashMap</tt> instance (the number of buckets) plus its size (the number of key-value
* mappings). Thus, it's very important not to set the initial capacity too high (or the load factor
* too low) if iteration performance is important.
*
* <p>An instance of <tt>HashMap</tt> has two parameters that affect its performance: <i>initial
* capacity</i> and <i>load factor</i>. The <i>capacity</i> is the number of buckets in the hash
* table, and the initial capacity is simply the capacity at the time the hash table is created. The
* <i>load factor</i> is a measure of how full the hash table is allowed to get before its capacity
* is automatically increased. When the number of entries in the hash table exceeds the product of
* the load factor and the current capacity, the hash table is <i>rehashed</i> (that is, internal
* data structures are rebuilt) so that the hash table has approximately twice the number of
* buckets.
*
* <p>As a general rule, the default load factor (.75) offers a good tradeoff between time and space
* costs. Higher values decrease the space overhead but increase the lookup cost (reflected in most
* of the operations of the <tt>HashMap</tt> class, including <tt>get</tt> and <tt>put</tt>). The
* expected number of entries in the map and its load factor should be taken into account when
* setting its initial capacity, so as to minimize the number of rehash operations. If the initial
* capacity is greater than the maximum number of entries divided by the load factor, no rehash
* operations will ever occur.
*
* <p>If many mappings are to be stored in a <tt>HashMap</tt> instance, creating it with a
* sufficiently large capacity will allow the mappings to be stored more efficiently than letting it
* perform automatic rehashing as needed to grow the table.
*
* <p><strong>Note that this implementation is not synchronized.</strong> If multiple threads access
* a hash map concurrently, and at least one of the threads modifies the map structurally, it
* <i>must</i> be synchronized externally. (A structural modification is any operation that adds or
* deletes one or more mappings; merely changing the value associated with a key that an instance
* already contains is not a structural modification.) This is typically accomplished by
* synchronizing on some object that naturally encapsulates the map.
*
* <p>If no such object exists, the map should be "wrapped" using the {@link
* Collections#synchronizedMap Collections.synchronizedMap} method. This is best done at creation
* time, to prevent accidental unsynchronized access to the map:
*
* <pre>
* Map m = Collections.synchronizedMap(new HashMap(...));</pre>
*
* <p>The iterators returned by all of this class's "collection view methods" are <i>fail-fast</i>:
* if the map is structurally modified at any time after the iterator is created, in any way except
* through the iterator's own <tt>remove</tt> method, the iterator will throw a {@link
* ConcurrentModificationException}. Thus, in the face of concurrent modification, the iterator
* fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an
* undetermined time in the future.
*
* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally
* speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent
* modification. Fail-fast iterators throw <tt>ConcurrentModificationException</tt> on a best-effort
* basis. Therefore, it would be wrong to write a program that depended on this exception for its
* correctness: <i>the fail-fast behavior of iterators should be used only to detect bugs.</i>
*
* <p>This class is a member of the <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @param <K> the type of keys maintained by this map
* @param <V> the type of mapped values
* @author Doug Lea
* @author Josh Bloch
* @author Arthur van Hoff
* @author Neal Gafter
* @see Object#hashCode()
* @see Collection
* @see Map
* @see TreeMap
* @see Hashtable
* @since 1.2
*/
public class HashMap<K, V> extends AbstractMap<K, V> implements Map<K, V>, Cloneable, Serializable {
/** The default initial capacity - MUST be a power of two. */
static final int DEFAULT_INITIAL_CAPACITY = 16;
/**
* The maximum capacity, used if a higher value is implicitly specified by either of the
* constructors with arguments. MUST be a power of two <= 1<<30.
*/
static final int MAXIMUM_CAPACITY = 1 << 30;
/** The load factor used when none specified in constructor. */
static final float DEFAULT_LOAD_FACTOR = 0.75f;
/** The table, resized as necessary. Length MUST Always be a power of two. */
transient Entry<K, V>[] table;
/** The number of key-value mappings contained in this map. */
transient int size;
/**
* The next size value at which to resize (capacity * load factor).
*
* @serial
*/
int threshold;
/**
* The load factor for the hash table.
*
* @serial
*/
final float loadFactor;
/**
* The number of times this HashMap has been structurally modified Structural modifications are
* those that change the number of mappings in the HashMap or otherwise modify its internal
* structure (e.g., rehash). This field is used to make iterators on Collection-views of the
* HashMap fail-fast. (See ConcurrentModificationException).
*/
transient int modCount;
/**
* The default threshold of map capacity above which alternative hashing is used for String keys.
* Alternative hashing reduces the incidence of collisions due to weak hash code calculation for
* String keys.
*
* <p>This value may be overridden by defining the system property {@code
* jdk.map.althashing.threshold}. A property value of {@code 1} forces alternative hashing to be
* used at all times whereas {@code -1} value ensures that alternative hashing is never used.
*/
static final int ALTERNATIVE_HASHING_THRESHOLD_DEFAULT = Integer.MAX_VALUE;
/** holds values which can't be initialized until after VM is booted. */
private static class Holder {
// Unsafe mechanics
/** Unsafe utilities */
static final sun.misc.Unsafe UNSAFE;
/** Offset of "final" hashSeed field we must set in readObject() method. */
static final long HASHSEED_OFFSET;
/** Table capacity above which to switch to use alternative hashing. */
static final int ALTERNATIVE_HASHING_THRESHOLD;
static {
String altThreshold =
java.security.AccessController.doPrivileged(
new sun.security.action.GetPropertyAction("jdk.map.althashing.threshold"));
int threshold;
try {
threshold =
(null != altThreshold)
? Integer.parseInt(altThreshold)
: ALTERNATIVE_HASHING_THRESHOLD_DEFAULT;
// disable alternative hashing if -1
if (threshold == -1) {
threshold = Integer.MAX_VALUE;
}
if (threshold < 0) {
throw new IllegalArgumentException("value must be positive integer.");
}
} catch (IllegalArgumentException failed) {
throw new Error("Illegal value for 'jdk.map.althashing.threshold'", failed);
}
ALTERNATIVE_HASHING_THRESHOLD = threshold;
try {
UNSAFE = sun.misc.Unsafe.getUnsafe();
HASHSEED_OFFSET = UNSAFE.objectFieldOffset(HashMap.class.getDeclaredField("hashSeed"));
} catch (NoSuchFieldException | SecurityException e) {
throw new Error("Failed to record hashSeed offset", e);
}
}
}
/**
* If {@code true} then perform alternative hashing of String keys to reduce the incidence of
* collisions due to weak hash code calculation.
*/
transient boolean useAltHashing;
/**
* A randomizing value associated with this instance that is applied to hash code of keys to make
* hash collisions harder to find.
*/
final transient int hashSeed = sun.misc.Hashing.randomHashSeed(this);
/**
* Constructs an empty <tt>HashMap</tt> with the specified initial capacity and load factor.
*
* @param initialCapacity the initial capacity
* @param loadFactor the load factor
* @throws IllegalArgumentException if the initial capacity is negative or the load factor is
* nonpositive
*/
public HashMap(int initialCapacity, float loadFactor) {
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal initial capacity: " + initialCapacity);
if (initialCapacity > MAXIMUM_CAPACITY) initialCapacity = MAXIMUM_CAPACITY;
if (loadFactor <= 0 || Float.isNaN(loadFactor))
throw new IllegalArgumentException("Illegal load factor: " + loadFactor);
// Find a power of 2 >= initialCapacity
int capacity = 1;
while (capacity < initialCapacity) capacity <<= 1;
this.loadFactor = loadFactor;
threshold = (int) Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
table = new Entry[capacity];
useAltHashing = sun.misc.VM.isBooted() && (capacity >= Holder.ALTERNATIVE_HASHING_THRESHOLD);
init();
}
/**
* Constructs an empty <tt>HashMap</tt> with the specified initial capacity and the default load
* factor (0.75).
*
* @param initialCapacity the initial capacity.
* @throws IllegalArgumentException if the initial capacity is negative.
*/
public HashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR);
}
/**
* Constructs an empty <tt>HashMap</tt> with the default initial capacity (16) and the default
* load factor (0.75).
*/
public HashMap() {
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);
}
/**
* Constructs a new <tt>HashMap</tt> with the same mappings as the specified <tt>Map</tt>. The
* <tt>HashMap</tt> is created with default load factor (0.75) and an initial capacity sufficient
* to hold the mappings in the specified <tt>Map</tt>.
*
* @param m the map whose mappings are to be placed in this map
* @throws NullPointerException if the specified map is null
*/
public HashMap(Map<? extends K, ? extends V> m) {
this(
Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, DEFAULT_INITIAL_CAPACITY),
DEFAULT_LOAD_FACTOR);
putAllForCreate(m);
}
// internal utilities
/**
* Initialization hook for subclasses. This method is called in all constructors and
* pseudo-constructors (clone, readObject) after HashMap has been initialized but before any
* entries have been inserted. (In the absence of this method, readObject would require explicit
* knowledge of subclasses.)
*/
void init() {}
/**
* Retrieve object hash code and applies a supplemental hash function to the result hash, which
* defends against poor quality hash functions. This is critical because HashMap uses power-of-two
* length hash tables, that otherwise encounter collisions for hashCodes that do not differ in
* lower bits. Note: Null keys always map to hash 0, thus index 0.
*/
final int hash(Object k) {
int h = 0;
if (useAltHashing) {
if (k instanceof String) {
return sun.misc.Hashing.stringHash32((String) k);
}
h = hashSeed;
}
h ^= k.hashCode();
// This function ensures that hashCodes that differ only by
// constant multiples at each bit position have a bounded
// number of collisions (approximately 8 at default load factor).
h ^= (h >>> 20) ^ (h >>> 12);
return h ^ (h >>> 7) ^ (h >>> 4);
}
/** Returns index for hash code h. */
static int indexFor(int h, int length) {
return h & (length - 1);
}
/**
* 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 contains no key-value mappings.
*
* @return <tt>true</tt> if this map contains no key-value mappings
*/
public boolean isEmpty() {
return size == 0;
}
/**
* 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==null ? k==null : key.equals(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.
*
* @see #put(Object, Object)
*/
public V get(Object key) {
if (key == null) return getForNullKey();
Entry<K, V> entry = getEntry(key);
return null == entry ? null : entry.getValue();
}
/**
* Offloaded version of get() to look up null keys. Null keys map to index 0. This null case is
* split out into separate methods for the sake of performance in the two most commonly used
* operations (get and put), but incorporated with conditionals in others.
*/
private V getForNullKey() {
for (Entry<K, V> e = table[0]; e != null; e = e.next) {
if (e.key == null) return e.value;
}
return null;
}
/**
* 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 getEntry(key) != null;
}
/**
* Returns the entry associated with the specified key in the HashMap. Returns null if the HashMap
* contains no mapping for the key.
*/
final Entry<K, V> getEntry(Object key) {
int hash = (key == null) ? 0 : hash(key);
for (Entry<K, V> e = table[indexFor(hash, table.length)]; e != null; e = e.next) {
Object k;
if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) return e;
}
return null;
}
/**
* Associates the specified value with the specified key in this map. If the map previously
* contained a mapping for the key, the old value is replaced.
*
* @param key key with which the specified value is to be associated
* @param value value to be associated with the specified key
* @return the previous value associated with <tt>key</tt>, or <tt>null</tt> if there was no
* mapping for <tt>key</tt>. (A <tt>null</tt> return can also indicate that the map previously
* associated <tt>null</tt> with <tt>key</tt>.)
*/
public V put(K key, V value) {
if (key == null) return putForNullKey(value);
int hash = hash(key);
int i = indexFor(hash, table.length);
for (Entry<K, V> e = table[i]; e != null; e = e.next) {
Object k;
if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
V oldValue = e.value;
e.value = value;
e.recordAccess(this);
return oldValue;
}
}
modCount++;
addEntry(hash, key, value, i);
return null;
}
/** Offloaded version of put for null keys */
private V putForNullKey(V value) {
for (Entry<K, V> e = table[0]; e != null; e = e.next) {
if (e.key == null) {
V oldValue = e.value;
e.value = value;
e.recordAccess(this);
return oldValue;
}
}
modCount++;
addEntry(0, null, value, 0);
return null;
}
/**
* This method is used instead of put by constructors and pseudoconstructors (clone, readObject).
* It does not resize the table, check for comodification, etc. It calls createEntry rather than
* addEntry.
*/
private void putForCreate(K key, V value) {
int hash = null == key ? 0 : hash(key);
int i = indexFor(hash, table.length);
/**
* Look for preexisting entry for key. This will never happen for clone or deserialize. It will
* only happen for construction if the input Map is a sorted map whose ordering is inconsistent
* w/ equals.
*/
for (Entry<K, V> e = table[i]; e != null; e = e.next) {
Object k;
if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) {
e.value = value;
return;
}
}
createEntry(hash, key, value, i);
}
private void putAllForCreate(Map<? extends K, ? extends V> m) {
for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
putForCreate(e.getKey(), e.getValue());
}
/**
* Rehashes the contents of this map into a new array with a larger capacity. This method is
* called automatically when the number of keys in this map reaches its threshold.
*
* <p>If current capacity is MAXIMUM_CAPACITY, this method does not resize the map, but sets
* threshold to Integer.MAX_VALUE. This has the effect of preventing future calls.
*
* @param newCapacity the new capacity, MUST be a power of two; must be greater than current
* capacity unless current capacity is MAXIMUM_CAPACITY (in which case value is irrelevant).
*/
void resize(int newCapacity) {
Entry[] oldTable = table;
int oldCapacity = oldTable.length;
if (oldCapacity == MAXIMUM_CAPACITY) {
threshold = Integer.MAX_VALUE;
return;
}
Entry[] newTable = new Entry[newCapacity];
boolean oldAltHashing = useAltHashing;
useAltHashing |=
sun.misc.VM.isBooted() && (newCapacity >= Holder.ALTERNATIVE_HASHING_THRESHOLD);
boolean rehash = oldAltHashing ^ useAltHashing;
transfer(newTable, rehash);
table = newTable;
threshold = (int) Math.min(newCapacity * loadFactor, MAXIMUM_CAPACITY + 1);
}
/** Transfers all entries from current table to newTable. */
void transfer(Entry[] newTable, boolean rehash) {
int newCapacity = newTable.length;
for (Entry<K, V> e : table) {
while (null != e) {
Entry<K, V> next = e.next;
if (rehash) {
e.hash = null == e.key ? 0 : hash(e.key);
}
int i = indexFor(e.hash, newCapacity);
e.next = newTable[i];
newTable[i] = e;
e = next;
}
}
}
/**
* 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 mappings to be stored in this map
* @throws NullPointerException if the specified map is null
*/
public void putAll(Map<? extends K, ? extends V> m) {
int numKeysToBeAdded = m.size();
if (numKeysToBeAdded == 0) return;
/*
* Expand the map if the map if the number of mappings to be added
* is greater than or equal to threshold. This is conservative; the
* obvious condition is (m.size() + size) >= threshold, but this
* condition could result in a map with twice the appropriate capacity,
* if the keys to be added overlap with the keys already in this map.
* By using the conservative calculation, we subject ourself
* to at most one extra resize.
*/
if (numKeysToBeAdded > threshold) {
int targetCapacity = (int) (numKeysToBeAdded / loadFactor + 1);
if (targetCapacity > MAXIMUM_CAPACITY) targetCapacity = MAXIMUM_CAPACITY;
int newCapacity = table.length;
while (newCapacity < targetCapacity) newCapacity <<= 1;
if (newCapacity > table.length) resize(newCapacity);
}
for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) put(e.getKey(), e.getValue());
}
/**
* Removes the mapping for the specified key from this map if present.
*
* @param key key whose mapping is to be removed from the map
* @return the previous value associated with <tt>key</tt>, or <tt>null</tt> if there was no
* mapping for <tt>key</tt>. (A <tt>null</tt> return can also indicate that the map previously
* associated <tt>null</tt> with <tt>key</tt>.)
*/
public V remove(Object key) {
Entry<K, V> e = removeEntryForKey(key);
return (e == null ? null : e.value);
}
/**
* Removes and returns the entry associated with the specified key in the HashMap. Returns null if
* the HashMap contains no mapping for this key.
*/
final Entry<K, V> removeEntryForKey(Object key) {
int hash = (key == null) ? 0 : hash(key);
int i = indexFor(hash, table.length);
Entry<K, V> prev = table[i];
Entry<K, V> e = prev;
while (e != null) {
Entry<K, V> next = e.next;
Object k;
if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) {
modCount++;
size--;
if (prev == e) table[i] = next;
else prev.next = next;
e.recordRemoval(this);
return e;
}
prev = e;
e = next;
}
return e;
}
/** Special version of remove for EntrySet using {@code Map.Entry.equals()} for matching. */
final Entry<K, V> removeMapping(Object o) {
if (!(o instanceof Map.Entry)) return null;
Map.Entry<K, V> entry = (Map.Entry<K, V>) o;
Object key = entry.getKey();
int hash = (key == null) ? 0 : hash(key);
int i = indexFor(hash, table.length);
Entry<K, V> prev = table[i];
Entry<K, V> e = prev;
while (e != null) {
Entry<K, V> next = e.next;
if (e.hash == hash && e.equals(entry)) {
modCount++;
size--;
if (prev == e) table[i] = next;
else prev.next = next;
e.recordRemoval(this);
return e;
}
prev = e;
e = next;
}
return e;
}
/** Removes all of the mappings from this map. The map will be empty after this call returns. */
public void clear() {
modCount++;
Entry[] tab = table;
for (int i = 0; i < tab.length; i++) tab[i] = null;
size = 0;
}
/**
* Returns <tt>true</tt> if this map maps one or more keys to the specified value.
*
* @param value value whose presence in this map is to be tested
* @return <tt>true</tt> if this map maps one or more keys to the specified value
*/
public boolean containsValue(Object value) {
if (value == null) return containsNullValue();
Entry[] tab = table;
for (int i = 0; i < tab.length; i++)
for (Entry e = tab[i]; e != null; e = e.next) if (value.equals(e.value)) return true;
return false;
}
/** Special-case code for containsValue with null argument */
private boolean containsNullValue() {
Entry[] tab = table;
for (int i = 0; i < tab.length; i++)
for (Entry e = tab[i]; e != null; e = e.next) if (e.value == null) return true;
return false;
}
/**
* Returns a shallow copy of this <tt>HashMap</tt> instance: the keys and values themselves are
* not cloned.
*
* @return a shallow copy of this map
*/
public Object clone() {
HashMap<K, V> result = null;
try {
result = (HashMap<K, V>) super.clone();
} catch (CloneNotSupportedException e) {
// assert false;
}
result.table = new Entry[table.length];
result.entrySet = null;
result.modCount = 0;
result.size = 0;
result.init();
result.putAllForCreate(this);
return result;
}
static class Entry<K, V> implements Map.Entry<K, V> {
final K key;
V value;
Entry<K, V> next;
int hash;
/** Creates new entry. */
Entry(int h, K k, V v, Entry<K, V> n) {
value = v;
next = n;
key = k;
hash = h;
}
public final K getKey() {
return key;
}
public final V getValue() {
return value;
}
public final V setValue(V newValue) {
V oldValue = value;
value = newValue;
return oldValue;
}
public final boolean equals(Object o) {
if (!(o instanceof Map.Entry)) return false;
Map.Entry e = (Map.Entry) o;
Object k1 = getKey();
Object k2 = e.getKey();
if (k1 == k2 || (k1 != null && k1.equals(k2))) {
Object v1 = getValue();
Object v2 = e.getValue();
if (v1 == v2 || (v1 != null && v1.equals(v2))) return true;
}
return false;
}
public final int hashCode() {
return (key == null ? 0 : key.hashCode()) ^ (value == null ? 0 : value.hashCode());
}
public final String toString() {
return getKey() + "=" + getValue();
}
/**
* This method is invoked whenever the value in an entry is overwritten by an invocation of
* put(k,v) for a key k that's already in the HashMap.
*/
void recordAccess(HashMap<K, V> m) {}
/** This method is invoked whenever the entry is removed from the table. */
void recordRemoval(HashMap<K, V> m) {}
}
/**
* Adds a new entry with the specified key, value and hash code to the specified bucket. It is the
* responsibility of this method to resize the table if appropriate.
*
* <p>Subclass overrides this to alter the behavior of put method.
*/
void addEntry(int hash, K key, V value, int bucketIndex) {
if ((size >= threshold) && (null != table[bucketIndex])) {
resize(2 * table.length);
hash = (null != key) ? hash(key) : 0;
bucketIndex = indexFor(hash, table.length);
}
createEntry(hash, key, value, bucketIndex);
}
/**
* Like addEntry except that this version is used when creating entries as part of Map
* construction or "pseudo-construction" (cloning, deserialization). This version needn't worry
* about resizing the table.
*
* <p>Subclass overrides this to alter the behavior of HashMap(Map), clone, and readObject.
*/
void createEntry(int hash, K key, V value, int bucketIndex) {
Entry<K, V> e = table[bucketIndex];
table[bucketIndex] = new Entry<>(hash, key, value, e);
size++;
}
private abstract class HashIterator<E> implements Iterator<E> {
Entry<K, V> next; // next entry to return
int expectedModCount; // For fast-fail
int index; // current slot
Entry<K, V> current; // current entry
HashIterator() {
expectedModCount = modCount;
if (size > 0) { // advance to first entry
Entry[] t = table;
while (index < t.length && (next = t[index++]) == null) ;
}
}
public final boolean hasNext() {
return next != null;
}
final Entry<K, V> nextEntry() {
if (modCount != expectedModCount) throw new ConcurrentModificationException();
Entry<K, V> e = next;
if (e == null) throw new NoSuchElementException();
if ((next = e.next) == null) {
Entry[] t = table;
while (index < t.length && (next = t[index++]) == null) ;
}
current = e;
return e;
}
public void remove() {
if (current == null) throw new IllegalStateException();
if (modCount != expectedModCount) throw new ConcurrentModificationException();
Object k = current.key;
current = null;
HashMap.this.removeEntryForKey(k);
expectedModCount = modCount;
}
}
private final class ValueIterator extends HashIterator<V> {
public V next() {
return nextEntry().value;
}
}
private final class KeyIterator extends HashIterator<K> {
public K next() {
return nextEntry().getKey();
}
}
private final class EntryIterator extends HashIterator<Map.Entry<K, V>> {
public Map.Entry<K, V> next() {
return nextEntry();
}
}
// Subclass overrides these to alter behavior of views' iterator() method
Iterator<K> newKeyIterator() {
return new KeyIterator();
}
Iterator<V> newValueIterator() {
return new ValueIterator();
}
Iterator<Map.Entry<K, V>> newEntryIterator() {
return new EntryIterator();
}
// Views
private transient Set<Map.Entry<K, V>> entrySet = null;
/**
* Returns a {@link 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 (except through the iterator's own <tt>remove</tt>
* operation), the results of the iteration are undefined. The set supports element removal, which
* removes the corresponding mapping from the map, via the <tt>Iterator.remove</tt>,
* <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations. It
* does not support the <tt>add</tt> or <tt>addAll</tt> operations.
*/
public Set<K> keySet() {
Set<K> ks = keySet;
return (ks != null ? ks : (keySet = new KeySet()));
}
private final class KeySet extends AbstractSet<K> {
public Iterator<K> iterator() {
return newKeyIterator();
}
public int size() {
return size;
}
public boolean contains(Object o) {
return containsKey(o);
}
public boolean remove(Object o) {
return HashMap.this.removeEntryForKey(o) != null;
}
public void clear() {
HashMap.this.clear();
}
}
/**
* Returns a {@link 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 (except through the
* iterator's own <tt>remove</tt> operation), the results of the iteration are undefined. The
* collection supports element removal, which removes the corresponding mapping from the map, via
* the <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>, <tt>removeAll</tt>,
* <tt>retainAll</tt> and <tt>clear</tt> operations. It does not support the <tt>add</tt> or
* <tt>addAll</tt> operations.
*/
public Collection<V> values() {
Collection<V> vs = values;
return (vs != null ? vs : (values = new Values()));
}
private final class Values extends AbstractCollection<V> {
public Iterator<V> iterator() {
return newValueIterator();
}
public int size() {
return size;
}
public boolean contains(Object o) {
return containsValue(o);
}
public void clear() {
HashMap.this.clear();
}
}
/**
* Returns a {@link Set} view of the mappings 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 (except through the iterator's own <tt>remove</tt>
* operation, or through the <tt>setValue</tt> operation on a map entry returned by the iterator)
* the results of the iteration are undefined. The set supports element removal, which removes the
* corresponding mapping from the map, via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
* <tt>removeAll</tt>, <tt>retainAll</tt> and <tt>clear</tt> operations. It does not support the
* <tt>add</tt> or <tt>addAll</tt> operations.
*
* @return a set view of the mappings contained in this map
*/
public Set<Map.Entry<K, V>> entrySet() {
return entrySet0();
}
private Set<Map.Entry<K, V>> entrySet0() {
Set<Map.Entry<K, V>> es = entrySet;
return es != null ? es : (entrySet = new EntrySet());
}
private final class EntrySet extends AbstractSet<Map.Entry<K, V>> {
public Iterator<Map.Entry<K, V>> iterator() {
return newEntryIterator();
}
public boolean contains(Object o) {
if (!(o instanceof Map.Entry)) return false;
Map.Entry<K, V> e = (Map.Entry<K, V>) o;
Entry<K, V> candidate = getEntry(e.getKey());
return candidate != null && candidate.equals(e);
}
public boolean remove(Object o) {
return removeMapping(o) != null;
}
public int size() {
return size;
}
public void clear() {
HashMap.this.clear();
}
}
/**
* Save the state of the <tt>HashMap</tt> instance to a stream (i.e., serialize it).
*
* @serialData The <i>capacity</i> of the HashMap (the length of the bucket array) is emitted
* (int), followed by the <i>size</i> (an int, the number of key-value mappings), followed by
* the key (Object) and value (Object) for each key-value mapping. The key-value mappings are
* emitted in no particular order.
*/
private void writeObject(java.io.ObjectOutputStream s) throws IOException {
Iterator<Map.Entry<K, V>> i = (size > 0) ? entrySet0().iterator() : null;
// Write out the threshold, loadfactor, and any hidden stuff
s.defaultWriteObject();
// Write out number of buckets
s.writeInt(table.length);
// Write out size (number of Mappings)
s.writeInt(size);
// Write out keys and values (alternating)
if (size > 0) {
for (Map.Entry<K, V> e : entrySet0()) {
s.writeObject(e.getKey());
s.writeObject(e.getValue());
}
}
}
private static final long serialVersionUID = 362498820763181265L;
/** Reconstitute the {@code HashMap} instance from a stream (i.e., deserialize it). */
private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException {
// Read in the threshold (ignored), loadfactor, and any hidden stuff
s.defaultReadObject();
if (loadFactor <= 0 || Float.isNaN(loadFactor))
throw new InvalidObjectException("Illegal load factor: " + loadFactor);
// set hashSeed (can only happen after VM boot)
Holder.UNSAFE.putIntVolatile(
this, Holder.HASHSEED_OFFSET, sun.misc.Hashing.randomHashSeed(this));
// Read in number of buckets and allocate the bucket array;
s.readInt(); // ignored
// Read number of mappings
int mappings = s.readInt();
if (mappings < 0) throw new InvalidObjectException("Illegal mappings count: " + mappings);
int initialCapacity =
(int)
Math.min(
// capacity chosen by number of mappings
// and desired load (if >= 0.25)
mappings * Math.min(1 / loadFactor, 4.0f),
// we have limits...
HashMap.MAXIMUM_CAPACITY);
int capacity = 1;
// find smallest power of two which holds all mappings
while (capacity < initialCapacity) {
capacity <<= 1;
}
table = new Entry[capacity];
threshold = (int) Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
useAltHashing = sun.misc.VM.isBooted() && (capacity >= Holder.ALTERNATIVE_HASHING_THRESHOLD);
init(); // Give subclass a chance to do its thing.
// Read the keys and values, and put the mappings in the HashMap
for (int i = 0; i < mappings; i++) {
K key = (K) s.readObject();
V value = (V) s.readObject();
putForCreate(key, value);
}
}
// These methods are used when serializing HashSets
int capacity() {
return table.length;
}
float loadFactor() {
return loadFactor;
}
}
