HashMap 1.7源码阅读

package app;
import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Arrays;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Set;

public class HashMap<K,V> extends AbstractMap<K,V> implements Map<K,V>, Cloneable, Serializable {

/*
HashMap 的实例有两个参数影响其性能：初始容量 和加载因子。
容量是哈希表中桶的数量，初始容量只是哈希表在创建时的容量。
加载因子是哈希表在其容量自动增加之前可以达到多满的一种尺度。
当哈希表中的条目数超出了加载因子与当前容量的乘积时，
则要对该哈希表进行 rehash 操作（即重建内部数据结构），
从而哈希表将具有大约两倍的桶数。
加载因子默认值为0.75，默认哈希表容量为16
*/

// The default initial capacity - MUST be a power of two.
// 默认HashMap的容量，初始化容量16 HashMap的容量必须是2的指数倍        【Hashtable是11】
static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16

// 最大容量2的30次方 。
// HashMap Bucket数组的长度,int 是4个字节存储，
// 去掉其符号位数为31位，再考虑到这里其实是定义HashMap Bucket数组的长度，考虑到Java堆存储空间的限制，定位30位，其大小为107****24。
static final int MAXIMUM_CAPACITY = 1 << 30;

// The load factor used when none specified in constructor.
// 默认加载因子默认的平衡因子为0.75，权衡了时间复杂度与空间复杂度之后的最好取值（JDK说是最好的），
// 过高的因子会降低存储空间但是查找（lookup，包括HashMap中的put与get方法）的时间就会增加。
static final float DEFAULT_LOAD_FACTOR = 0.75f;

// An empty table instance to share when the table is not inflated.
// 空的Entry的二维数组,用来存储键值对的Entry数组,用于设置刚刚初始化的HashMap对象,用来减少存储空间
static final Entry<?,?>[] EMPTY_TABLE = {};

// transient 表明该数据不参与序列化？为什么用transient
// 1.transient 首先是表明该数据不参与序列化。假设HashMap 中的存储数据的数组还有很多的空间没有被使用，
// 没有被使用到的空间被序列化没有意义。所以下文会有手动使用 writeObject() 方法，只序列化实际存储元素的数组。
// 2. 不同的虚拟机对于相同 hashCode 产生的 Code 值可能是不一样的，如果使用默认序列化，则反序列化后，元素的位置和之前的是保持一致的，
// 可是由于 hashCode 的值不一样了，那么后续看到的定位函数 indexOf（）返回的元素下标就会不同，其结果会出差错。

// The table, resized as necessary. Length MUST Always be a power of two.
// **HashMap底层Bucket数组
transient Entry<K,V>[] table = (Entry<K,V>[]) EMPTY_TABLE;

/**
* The number of key-value mappings contained in this map.
*/
// 当前HashMap键值对K/V数据的大小
transient int size;

// The next size value at which to resize (capacity * load factor).
// If table == EMPTY_TABLE then this is the initial capacity at which the
// table will be created when inflated.
// 阀值（threshold = capacity * loadFactor ），当size超过threshold时，table将会扩容.
int threshold;

// The load factor for the hash table.
// 负载因子
final float loadFactor;

// Fail-Fast机制：java.util.HashMap非线程安全，如果在使用迭代器的过程中有其他线程修改了map，会抛出ConcurrentModificationException
// 记录HashMap修改次数，如增、删元素或rehash。这个字段被用来当迭代器的fail-fast检查线程是否同步
transient int modCount;

//默认的阀值
static final int ALTERNATIVE_HASHING_THRESHOLD_DEFAULT = Integer.MAX_VALUE;

// Holder是为了加载获取threshold的配置参数。
private static class Holder {
/**
* Table capacity above which to switch to use alternative hashing.
*/
static final int ALTERNATIVE_HASHING_THRESHOLD;
static {
// JDK 1.7新加，针对字符串的key的hash算法会提供更好的hashcode分布减少冲突；
// 如果想启用此特性，需设置jdk.map.althashing.threshold系统属性的值为一个非负数（默认是-1）这个值代表了一个集合大小的threshold，
// 超过这个值，就会使用新的hash算法。需要注意的一点，只有当re-hash的时候，新的hash算法才会起作用。
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;
}
}

// If 0 then alternative hashing is disabled.
// 用于hash的种子
transient int hashSeed = 0;

//构造函数：使用初始化容量和加载因子初始化HashMap
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);

this.loadFactor = loadFactor;
threshold = initialCapacity;

// init() hook because : HashMap是可序列化的，而反序列化方法（readObject()）是一个跟构造器性质相似、但却不是构造器的奇怪的东西.
// 为了让子类能方便规整地实现构造初始化与反序列初始化的功能，HashMap就在构造器末尾和反序列化方法末尾都埋了这个init()钩子，
// 这样子类就不用为这两种不同的初始化需求而重复头疼了。
// jdk8 改名为reinitialize(),
// LinkedHashMap要维持插入顺序，为此它会把所有插入的节点（键值对）用双向链表串在一起。而在它的init()实现里，它就创建并初始化了该双向链表的头节点。
init();
}

// Constructs ,指定负载因子
public HashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR);
}

/**
* Constructs 使用默认容量和加载因子初始化HashMap
*/
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
*/
// 从一个已有的Map创建一个新的HashMap
public HashMap(Map<? extends K, ? extends V> m) {
this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR);
inflateTable(threshold);
putAllForCreate(m);
}

// 将number扩展成2的倍数 ,返回比入参初始容量大的最小的2的幂数
private static int roundUpToPowerOf2(int number) {
// assert number >= 0 : "number must be non-negative";
int rounded = number >= MAXIMUM_CAPACITY
? MAXIMUM_CAPACITY
: (rounded = Integer.highestOneBit(number)) != 0
? (Integer.bitCount(number) > 1) ? rounded << 1 : rounded
: 1;
return rounded;
}

/**
* 【JDK 1.7新加】Inflates the table. 扩充 HASHMAP 容量
*/
private void inflateTable(int toSize) {
// Find a power of 2 >= toSize
int capacity = roundUpToPowerOf2(toSize);
//重新设置阀值
threshold = (int) Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
table = new Entry[capacity];
initHashSeedAsNeeded(capacity);
}

/**
* 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.)
*/
// 内部使用,可作为一个钩子来被子类使用，它已经作为模版模式被所有的构造器，clone等调用。
void init() {
}

// Initialize the hashing mask value. We defer initialization until we really need it.
final boolean initHashSeedAsNeeded(int capacity) {
boolean currentAltHashing = hashSeed != 0;
//根据系统函数得到一个hash
boolean useAltHashing = sun.misc.VM.isBooted() &&
(capacity >= Holder.ALTERNATIVE_HASHING_THRESHOLD);
boolean switching = currentAltHashing ^ useAltHashing;
//如果hashSeed初始化为0则跳过switching
//否则使用系统函数得到新的hashSeed
if (switching) {
hashSeed = useAltHashing
? sun.misc.Hashing.randomHashSeed(this)
: 0;
}
return switching;
}

/**
* 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.
*/
// 哈希算法的核心：哈希函数 ,用来计算对象的hash值
final int hash(Object k) {
int h = hashSeed;
//通过hashSeed初始化的值的不同来选择不同的hash方式
if (0 != h && k instanceof String) {
//String类采用不同的hash函数
return sun.misc.Hashing.stringHash32((String) k);
}

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.
// 通过得到的hash值来确定返回hash code对应的length中的下标
static int indexFor(int h, int length) {
// assert Integer.bitCount(length) == 1 : "length must be a non-zero power of 2";
return h & (length-1);
}

// 当前HashMap键值对K/V数据的大小
public int size() {
return size;
}

// Returns <tt>true</tt> if this map contains no key-value mappings.
public boolean isEmpty() {
return size == 0;
}

public V get(Object key) {
if (key == null)
return getForNullKey();
Entry<K,V> entry = getEntry(key);

return null == entry ? null : entry.getValue();
}

private V getForNullKey() {
if (size == 0) {
return null;
}
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) {
if (size == 0) {
return null;
}
//通过key的hash值确定table下标（null对应下标0）
int hash = (key == null) ? 0 : hash(key);
// 遍历table中的 entry数组
for (Entry<K,V> e = table[indexFor(hash, table.length)]; e != null; e = e.next) {
Object k;
// 因为存在不同的key对应相同的hash值，还要判读key是否一样
if ( e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k))) )
return e;
}
return null;
}

//
// 通过key的hash值确定table下标，如果key已经存在则更新，不存在则调用addEntry方法
public V put(K key, V value) {
if (table == EMPTY_TABLE) {
inflateTable(threshold);
}
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;
// 因为存在不同的key对应相同的hash值，还要判读key是否一样
if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
V oldValue = e.value;
e.value = value;
e.recordAccess(this);
return oldValue; // 如果已经存在，更新值
}
}

// //上面的循环结束表示当前的key不存在与表中，需要另外增加
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());
}

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, initHashSeedAsNeeded(newCapacity));
table = newTable;
threshold = (int)Math.min(newCapacity * loadFactor, MAXIMUM_CAPACITY + 1);
}

/**
* Transfers all entries from current table to newTable.
*/
// 复制目前HashMap
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;
//是否重新进行hash计算
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;

if (table == EMPTY_TABLE) {
inflateTable((int) Math.max(numKeysToBeAdded * loadFactor, threshold));
}

/*
* 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) {
if (size == 0) {
return null;
}
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 (size == 0 || !(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++;
Arrays.fill(table, 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;
}
if (result.table != EMPTY_TABLE) {
result.inflateTable(Math.min(
(int) Math.min(
size * Math.min(1 / loadFactor, 4.0f),
// we have limits...
HashMap.MAXIMUM_CAPACITY),
table.length));
}
result.entrySet = null;
result.modCount = 0;
result.size = 0;
result.init();
result.putAllForCreate(this);

return result;
}

// 核心数据结构,数组+（单项）链表，LinkHashMap 是双向链表
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 Objects.hashCode(getKey()) ^ Objects.hashCode(getValue());
}

public final String toString() {
return getKey() + "=" + getValue();
}

// LinkedHashMap 有实现
void recordAccess(HashMap<K,V> m) {
}

// This method is invoked whenever the entry is removed from the table.
void recordRemoval(HashMap<K,V> m) {}
}

//
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);
}

// 它把新建的Entry节点node作为头部,链上之前的链表
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++;
}

// 类似于Entry数组的迭代器，主要是对table进行操作
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();
}

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();
}
}

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 {
// Write out the threshold, loadfactor, and any hidden stuff
s.defaultWriteObject();

// Write out number of buckets
if (table==EMPTY_TABLE) {
s.writeInt(roundUpToPowerOf2(threshold));
} else {
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;

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 other fields that need values
table = (Entry<K,V>[]) EMPTY_TABLE;

// Read in number of buckets
s.readInt(); // ignored.

// Read number of mappings
int mappings = s.readInt();
if (mappings < 0)
throw new InvalidObjectException("Illegal mappings count: " +
mappings);

// capacity chosen by number of mappings and desired load (if >= 0.25)
int capacity = (int) Math.min(
mappings * Math.min(1 / loadFactor, 4.0f),
// we have limits...
HashMap.MAXIMUM_CAPACITY);

// allocate the bucket array;
if (mappings > 0) {
inflateTable(capacity);
} else {
threshold = capacity;
}

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;   }
}