JDK版本：1.8package java.util;
import java.io.*;
public class HashMap<K,V>
extends AbstractMap<K,V>
implements Map<K,V>, Cloneable, Serializable
{
// 默认的初始容量
static final int DEFAULT_INITIAL_CAPACITY = 16;
// 最大容量
static final int MAXIMUM_CAPACITY = 1 << 30;
// 加载因子0.75
static final float DEFAULT_LOAD_FACTOR = 0.75f;
transient Entry[] table;
transient int size;
int threshold;
final float loadFactor;
transient volatile int modCount;
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);
int capacity = 1;
while (capacity < initialCapacity)
capacity <<= 1;
this.loadFactor = loadFactor;
threshold = (int)(capacity * loadFactor);
table = new Entry[capacity];
init();
}
public HashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR);
}
public HashMap() {
this.loadFactor = DEFAULT_LOAD_FACTOR;
// 当HashMap中存储数据的数量达到threshold时，就需要将HashMap的容量加倍。
threshold = (int)(DEFAULT_INITIAL_CAPACITY * DEFAULT_LOAD_FACTOR);
// 创建Entry数组，用来保存数据
table = new Entry[DEFAULT_INITIAL_CAPACITY];
init();
}
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);
}
static int hash(int h) {
h ^= (h >>> 20) ^ (h >>> 12);
return h ^ (h >>> 7) ^ (h >>> 4);
}
static int indexFor(int h, int length) {
return h & (length-1);
}
public int size() {
return size;
}
public boolean isEmpty() {
return size == 0;
}
public V get(Object key) {
if (key == null)
return getForNullKey();
int hash = hash(key.hashCode());
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.equals(k)))
return e.value;
}
return null;
}
private V getForNullKey() {
for (Entry<K,V> e = table[0]; e != null; e = e.next) {
if (e.key == null)
return e.value;
}
return null;
}
public boolean containsKey(Object key) {
return getEntry(key) != null;
}
final Entry<K,V> getEntry(Object key) {
int hash = (key == null) ? 0 : hash(key.hashCode());
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;
}
public V put(K key, V value) {
// 若“key为null”，则将该键值对添加到table[0]中。
if (key == null)
return putForNullKey(value);
int hash = hash(key.hashCode());
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;
}
// 将key==null键值对添加到table[0]位置
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;
}
private void putForCreate(K key, V value) {
int hash = (key == null) ? 0 : hash(key.hashCode());
int i = indexFor(hash, table.length);
// 若该HashMap表中存在“键值等于key”的元素，则替换该元素的value值
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) {
// 利用迭代器将元素逐个添加到HashMap中
for (Iterator<? extends Map.Entry<? extends K, ? extends V>> i = m.entrySet().iterator(); i.hasNext(); ) {
Map.Entry<? extends K, ? extends V> e = i.next();
putForCreate(e.getKey(), e.getValue());
}
}
// 重新调整HashMap的大小，newCapacity是调整后的容量
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];
transfer(newTable);
table = newTable;
threshold = (int)(newCapacity * loadFactor);
}
void transfer(Entry[] newTable) {
Entry[] src = table;
int newCapacity = newTable.length;
for (int j = 0; j < src.length; j++) {
Entry<K,V> e = src[j];
if (e != null) {
src[j] = null;
do {
Entry<K,V> next = e.next;
int i = indexFor(e.hash, newCapacity);
e.next = newTable[i];
newTable[i] = e;
e = next;
} while (e != null);
}
}
}
public void putAll(Map<? extends K, ? extends V> m) {
// 有效性判断
int numKeysToBeAdded = m.size();
if (numKeysToBeAdded == 0)
return;
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);
}
// 通过迭代器，将“m”中的元素逐个添加到HashMap中。
for (Iterator<? extends Map.Entry<? extends K, ? extends V>> i = m.entrySet().iterator(); i.hasNext(); ) {
Map.Entry<? extends K, ? extends V> e = i.next();
put(e.getKey(), e.getValue());
}
}
// 删除“键为key”元素
public V remove(Object key) {
Entry<K,V> e = removeEntryForKey(key);
return (e == null ? null : e.value);
}
final Entry<K,V> removeEntryForKey(Object key) {
int hash = (key == null) ? 0 : hash(key.hashCode());
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;
}
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.hashCode());
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;
}
public void clear() {
modCount++;
Entry[] tab = table;
for (int i = 0; i < tab.length; i++)
tab[i] = null;
size = 0;
}
public boolean containsValue(Object value) {
// 若“value为null”，则调用containsNullValue()查找
if (value == null)
return containsNullValue();
// 若“value不为null”，则查找HashMap中是否有值为value的节点。
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;
}
// 是否包含null值
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;
}
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;
}
// Entry是单向链表。
// 它是 “HashMap链式存储法”对应的链表。
// 它实现了Map.Entry 接口，即实现getKey(), getValue(), setValue(V value), equals(Object o), hashCode()这些函数
static class Entry<K,V> implements Map.Entry<K,V> {
final K key;
V value;
// 指向下一个节点
Entry<K,V> next;
final int hash;
// 构造函数。
// 输入参数包括"哈希值(h)", "键(k)", "值(v)", "下一节点(n)"
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;
}
// 判断两个Entry是否相等
// 若两个Entry的“key”和“value”都相等，则返回true。
// 否则，返回false
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;
}
// 实现hashCode()
public final int hashCode() {
return Objects.hashCode(key) ^ Objects.hashCode(value); }
public
final
String toString() {
return getKey() +
“=” + getValue(); }
void recordAccess(
HashMap<K,V> m) { }
// 当从HashMap中删除元素时，绘调用recordRemoval()。
// 这里不做任何处理
void recordRemoval(
HashMap<K,V> m) { } }
void addEntry(
int hash, K
key, V value,
int bucketIndex) { Entry<K,V> e = table[bucketIndex]; table[bucketIndex] =
new Entry<K,V>(hash,
key, value, e);
// 若HashMap的实际大小 不小于 “阈值”，则调整HashMap的大小
if (
size++ >= threshold) resize(
2 * table.length); }
void createEntry(
int hash, K
key, V value,
int bucketIndex) { Entry<K,V> e = table[bucketIndex]; table[bucketIndex] =
new Entry<K,V>(hash,
key, value, e);
size++; }
private
abstract class HashIterator<E> implements Iterator<E> {
// 下一个元素 Entry<K,V> next;
// expectedModCount用于实现fast-fail机制。
int expectedModCount;
// 当前索引
int index;
// 当前元素 Entry<K,V> current; 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; }
// 获取下一个元素
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; }
// 删除当前元素
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(); } } Iterator<K> newKeyIterator() {
return
new KeyIterator(); } Iterator<V> newValueIterator() {
return
new ValueIterator(); }
Iterator<Map.Entry<K,V>> newEntryIterator() {
return
new EntryIterator(); }
private
transient Set<Map.Entry<K,V>> entrySet =
null;
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(); } }
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(); } }
// 返回“HashMap的Entry集合”
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(); } }
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); s.writeInt(
size);
if (i !=
null) {
while (i.hasNext()) { Map.Entry<K,V> e = i.next(); s.writeObject(e.getKey()); s.writeObject(e.getValue()); } } }
private
static
final
long serialVersionUID =
362498820763181265L;
private
void readObject(java.io.ObjectInputStream s)
throws IOException, ClassNotFoundException {
// Read in the threshold, loadfactor, and any hidden stuff s.defaultReadObject();
// Read in number of buckets and allocate the bucket array;
int numBuckets = s.readInt(); table =
new Entry[numBuckets]; init();
// Give subclass a chance to do its thing.
// 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(); putForCreate(
key, value); } }
int capacity() {
return table.length; }
float loadFactor() {
return loadFactor; } }
