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

HashMap继承自AbstractMap，实现了Map接口，有map的基本操作；实现了Cloneable接口，使得该类是可克隆的；实现了Serializable接口，说明该类支持序列化。HashMap是线程不安全的。源码版本为JDK1.7.0_75

HashMap的数据结构

紫色的对应Entry<K,V>[] table，绿色的是Entry<K,V>对象队列，解决hash冲突。

在put时，首先调用hashCode方法获得哈希值，在调用indexFor方法获取该key存放在table数组的下标index，新建entry插入到index所指向的链表的队首。在删除时也是通过相同的方法找到该key所在的index，然后遍历链表，将key相同、hash值相等的entry删除。

HashMap还对map存放的key-value数目进行限制（使用threshold），且要求数组大小（capacity）必须是2的幂次方（考虑indexFor方法），当容量无法将entry全部保存或者entry数目超过threshold时，根据loadfactor使用resize对容量进行扩大，其中threshold=capacity*loadfactor。

HashMap中允许存放key为null的entry，对于key为null，其index为0。

inflateTable方法是在当table==EMPTY_TABLE时才用到,用于初始化table。

成员变量

   /**
     * 默认初始化空间——必须为2的倍数
     * The default initial capacity - MUST be a power of two.
     */
    static final int DEFAULT_INITIAL_CAPACITY = 1 << 4;// aka 16
 
    /**
     * 最大空间，若在构造方法中没有给定，则使用该值——必须为2的倍数
     * 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;
 
    /**
* 若在构造时没有指出则使用该值作为加载因子
     * The load factor used when none specified in constructor.
     */
    static final float DEFAULT_LOAD_FACTOR = 0.75f;
 
    /**
     * 当表格没有膨胀，则空表实例
     * An empty table instance to share when the table is not inflated.
     */
    static final Entry<?,?>[] EMPTY_TABLE = {};
 
    /**
     * 哈希表，有必要时需resize。长度总是2的倍数
     * The table, resized as necessary. Length MUST Always be a power of two.
     */
    transient Entry<K,V>[]table = (Entry<K,V>[]) EMPTY_TABLE;
 
    /**
     * map中包含的key-value映射数目
     * The number of key-value mappings contained in this map.
     */
    transient int size;
 
    /**
     * 调整大小的值？？临界值，当实际大小超过临界值时，会进行resize,threshold=capacity*load factor
     * The next size value at which to resize (capacity * load factor).
     * @serial
     */
    // If table == EMPTY_TABLE then this is the initial capacity at which the
    // table will be created when inflated.
    int threshold;
 
    /**
     * 哈希表的加载因子
     * The load factor for the hash table.
     *
     * @serial
     */
    final float loadFactor;
 
    /**
     * HashMap进行结构上修改的次数。用来是对HashMap的集合上的迭代器fast-fail
     * 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;
 
    /**
     * 当使用string作为键值的哈希时的map容量的默认阈值。。。
     * 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;
    /**
     * 随机值，用在keys的hash code上，使得哈希冲突较难发生。若该值为0，则alternative hash不可用（我理解的是二次哈希）
     * A randomizing value associated with this instance that is applied to
     * hash code of keys to make hash collisions harder to find. If 0 then
     * alternative hashing is disabled.
     */
    transient int hashSeed = 0;

冲突机会越大，则查找效率将降低。loadFactor为加载因子，表示hash表中元素的填满程度，加载因子越大，空间利用率高，但冲突机会就加大了，链表长度会越来越长，查找效率将降低；反之，加载因子越小，填满的元素越少，冲突机会减少，但空间浪费了。

因此，需要在“冲突机会”与“空间利用率”之间寻找平衡——类似“时空”平衡。

参考：

http://www.cnblogs.com/ITtangtang/p/3948406.html

私有静态内部类Holder

    /**
     * 保存那些直到虚拟机启动时才能初始化的值
     * holds values which can't be initialized until after VM is booted.
     */
    private static class Holder {
 
        /**
         * 当转向使用alternative hashing时，table的容量
         * 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(IllegalArgumentExceptionfailed) {
                throw new Error("Illegal value for 'jdk.map.althashing.threshold'",failed);
            }
 
            ALTERNATIVE_HASHING_THRESHOLD =threshold;
        }
    }

构造函数 

  /**
     * 指定了初始容量和加载因子，构造一个空HashMap
     * 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(intinitialCapacity, floatloadFactor) {
        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();
    }
 
    /**
     * 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(intinitialCapacity) {
        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);
        inflateTable(threshold);
 
        putAllForCreate(m);
    }

inflateTable，该方法在table==EMPTY_TABLE时被调用，用于
初始化
table，并将capacity提至2的幂次方。 

  private static int roundUpToPowerOf2(intnumber) {
        // assert number >= 0 : "number must be non-negative";
        return number >= MAXIMUM_CAPACITY
                ? MAXIMUM_CAPACITY
                : (number > 1) ? Integer.highestOneBit((number - 1) << 1) : 1;
    }   
/**
     * Inflates the table.
     */
    private void inflateTable(inttoSize) {
        // Find a power of 2 >= toSize
        int capacity = roundUpToPowerOf2(toSize);
 
        threshold = (int) Math.min(capacity *loadFactor, MAXIMUM_CAPACITY + 1);
        table = new Entry[capacity];
        initHashSeedAsNeeded(capacity);
    }
 
    // internal utilities
 
    /**
     * 为子类初始化hook（钩子）。该方法在构造方法和伪构造方法（clone，readObject）中初始化HashMap之后entry被插入之前调用的。没有该方法，readObject将需要子类信息。
     * 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() {
    }
 
    /**
     * 初始化哈希mask值。直到真的需要用到hashseed时，才初始化它。
     * Initialize the hashing mask value. We defer initialization until we
     * really need it.
     */
    final boolean initHashSeedAsNeeded(intcapacity) {
        boolean currentAltHashing = hashSeed != 0;
        boolean useAltHashing = sun.misc.VM.isBooted() &&
                (capacity >= Holder.ALTERNATIVE_HASHING_THRESHOLD);
        boolean switching = currentAltHashing ^ useAltHashing;
        if (switching) {
            hashSeed = useAltHashing
                ? sun.misc.Hashing.randomHashSeed(this)
                : 0;
        }
        return switching;
    }

hashing相关 

    /**
     * 获得对象哈希码，并将一个补充的哈希函数应用到哈希结果以防poor哈希函数。
     *  注意：键为null总是映射到哈希0，因此索引为0。
     * 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 = hashSeed;
        if (0 != h && k instanceof String) {
            return sun.misc.Hashing.stringHash32((String)k);
        }
 
        h ^= k.hashCode();
        // 通过若干次移位、异或操作，把hashCode的1的位置变得“松散，均匀”，
                    //  以免在计算index时不均匀
                    //  等价于操作 h ^ (h >>> 4) ^ (h >>> 7) ^ (h >>> 12) ^ (h >>> 16) ^ (h >>> 20) ^ (h >>> 24) ^ (h >>> 27);
                     // 将hashcode用十六进制表示为…nmlkjihgfedcba，则a'=a^b^c…,b'=b^c^d…,c'=c^d^e…
        // 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);
        returnh ^ (h >>> 7) ^ (h >>> 4);
    }
 
    /**
     * 返回哈希码h的索引
     *   因为length为2的幂次方，因此length-1使用二进制表示所有位都是1，即111111..，h&(length-1)得到的数可以均匀分布到table数组上，例如length=8，则1&7=1,2&7=2,3&7=3,…7&7=7,8&7=0,9&7=1..，可以看出该公式相当于h%length，注意的是针对length要为2的幂次方。
     * Returns index for hash code h.
     */
    static int indexFor(inth, intlength) {
        // assert Integer.bitCount(length) == 1 : "length must be a non-zero power of 2";
        return h & (length-1);
    }

Get key相关 

   /**
     * 返回给定key在map上对应的value，若map中没有该key，则返回null。
     * 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();
    }
 
    /**
      * 获取key为null所对应的value。前面提到key为null对应的索引为0，因此从table[0]
      *  开始遍历。
     * 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() {
        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;
    }
 
    /**
     * 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(Objectkey) {
        if (size == 0) {
            return null;
        }
 
        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;
    }

Put 相关 

   /**
     * 根据key值将key-value对插入到map中，若key已存在，则更新value。返回插入前map
     * 中key所对应的value值。
     * 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 (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;
            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;
    }
 
    /**
     * 设置key为null时的value值。
     * Offloaded version of put for null keys
     */
    private V putForNullKey(Vvalue) {
        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;
    }
 
    /**
     * 不同于put，该方法不需要resize table，构造方法或伪构造方法(clone，readObject)调用该方法。
     * 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());
    }

Resize 

   /**
     * 将原来map内容重哈希到一个更大容量的新数组上。当map中key数目达到threshold时，自动调用该方法。若当前容量为MAXIMUM_CAPACITY，则不resize map，设置threshold为Integer.MAX_VALUE。
     * 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.
     *
     * 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(intnewCapacity) {
        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);
    }
 
    /**
     * 将当前表中所有entry转换到newTable中。rehash标志转换时是否需要重哈希。
     * 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;
            }
        }
    }

将m中的key-value对全都复制到map中，在put之前，首先对table进行resize，若要添加的键-值对大于threshold，则对table进行resize。 

  /**
     * 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());
    }

删除。。。删除特定key，首先根据key，计算hash，得到索引，获取所在的“桶”，遍历桶内的
链表，删除hash相等且key相等的entry。 

   /**
     * 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(Objectkey) {
        Entry<K,V> e = removeEntryForKey(key);
        return (e ==null ? null :e.value);
    }
 
    /**
     * 删除并返回key所对应的entry，若map中不存在该key，返回null。
     * 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(Objectkey) {
        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;
    }
 
 
    /**
     * 根据Map.Entry.equals方法找出与对象o相匹配的entry，将其删除。
     * Special version of remove for EntrySet using {@code Map.Entry.equals()}
     * for matching.
     */
    final Entry<K,V> removeMapping(Objecto) {
        if (size == 0 || !(oinstanceof 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;
    }

  /**
     * 删除map中所有映射，使用Arrays.fill方法将table数组的值都设为null
     * 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;
    }

containXXX类方法

 /**
     * 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 (inti = 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 (inti = 0; i < tab.length ; i++)
            for (Entry e = tab[i] ;e != null ;e = e.next)
                if (e.value ==null)
                    return true;
        return false;
    }

clone方法 

 /**
     * 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 (CloneNotSupportedExceptione) {
            // 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;
    }

静态内部类Entry 

 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 (!(oinstanceof 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();
        }
 
        /**
         * 当entry的值通过调用put方法被重写时该方法将被调用
         * 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) {
        }
 
        /**
         * 当entry从table中删除时该方法将被调用
         * This method is invoked whenever the entry is
         * removed from the table.
         */
        void recordRemoval(HashMap<K,V>m) {
        }
    }

entry相关操作 

   /**
     * 添加一个新的entry。
     * 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.
     *
     * Subclass overrides this to alter the behavior of put method.
     */
    void addEntry(inthash, K key, Vvalue, intbucketIndex) {
        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);
    }
 
    /**
     * 创建entry，并将其添加到table[bucketIndex]队首中。
     * 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.
     *
     * Subclass overrides this to alter the behavior of HashMap(Map),
     * clone, and readObject.
     */
    void createEntry(inthash, K key, Vvalue, intbucketIndex) {
        Entry<K,V> e = table[bucketIndex];
        table[bucketIndex] =new Entry<>(hash,key, value,e);
        size++;
    }

迭代。。。。（没看） 

私有内部类KeySet及相关方法

私有内部类Value及其相关方法

私有内部类EntrySet及相关方法

参考：

http://www.cnblogs.com/ITtangtang/p/3948406.html

http://blog.csdn.net/dyllove98/article/details/9207601