package java.util;
import java.io.*;



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

    static final int DEFAULT_INITIAL_CAPACITY = 16;//默认容量

   
    static final int MAXIMUM_CAPACITY = 1 << 30;//最大容量

   
    static final float DEFAULT_LOAD_FACTOR = 0.75f;//加载因子
    transient Entry[] table;//一个数组用hash函数定位

   /*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。*/
    transient int size;//长度

  //使用transient修饰符来标识一个成员变量在序列化子系统中应被忽略

    int threshold;

   
    final float loadFactor;
/*Volatile修饰的成员变量在每次被线程访问时，都强迫从主内存中重读该成员变量的值。而且，当成员变量发生变化时，强迫线程将变化值回写到主内存。这样在任何时刻，两个不同的线程总是看到某个成员变量的同一个值。   */
    
    transient volatile int modCount;//这也是用于快速失败的

 public HashMap(int initialCapacity, float loadFactor) {//自己制定容量和加载因子
        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)(capacity * loadFactor);
        table = new Entry[capacity];
        init();
    }

   
    public HashMap(int initialCapacity) {
        this(initialCapacity, DEFAULT_LOAD_FACTOR);
    }

   
    public HashMap() {
        this.loadFactor = DEFAULT_LOAD_FACTOR;
        threshold = (int)(DEFAULT_INITIAL_CAPACITY * DEFAULT_LOAD_FACTOR);
        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);
    }

  
    void init() {
    }

   
    static int hash(int h) {
        // 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);//无符号右移一位
        return h ^ (h >>> 7) ^ (h >>> 4);//^异或运算
    }

   
    static int indexFor(int h, int length) {
        return h & (length-1);//&位与
    }

  
    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());//key使用hash函数定位 for (Entry e = table[indexFor(hash, table.length)];//取出值链式存储的 e != null; e = e.next) { Object k; if (e.hash == hash && ((k = e.key) == key || key.equals(k)))//hash一样equals一样就一样了 return e.value; } return null; } private V getForNullKey() { for (Entry e = table[0]; e != null; e = e.next) { if (e.key == null) return e.value;//得到空键的值。。 } return null; } public boolean containsKey(Object key) { return getEntry(key) != null;//没有键的值对应是null的 } final Entry getEntry(Object key) { int hash = (key == null) ? 0 : hash(key.hashCode());//null hash就是0 for (Entry 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) { if (key == null) return putForNullKey(value); int hash = hash(key.hashCode());//调用自己写的hashcode int i = indexFor(hash, table.length);//索引之后才完成了定位啊 for (Entry 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++;//呵呵 addEntry(hash, key, value, i); return null; } private V putForNullKey(V value) { for (Entry e = table[0]; e != null; e = e.next) { if (e.key == null) { V oldValue = e.value; e.value = value; e.recordAccess(this); return oldValue;//NULL的值只能有一个put会产生覆盖 } } 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); for (Entry 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 (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()); } } //数组重现变化吧 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 e = src[j]; if (e != null) { src[j] = null; do { Entry next = e.next; int i = indexFor(e.hash, newCapacity); e.next = newTable[i];//复制老东西 newTable[i] = e; e = next; } while (e != null); } } } public void putAll(Map<? extends K, ? extends V> m) { 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); } 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()); } } public V remove(Object key) { Entry e = removeEntryForKey(key); return (e == null ? null : e.value); } final Entry removeEntryForKey(Object key) { int hash = (key == null) ? 0 : hash(key.hashCode()); int i = indexFor(hash, table.length); Entry prev = table[i]; Entry e = prev; while (e != null) { Entry 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. */ final Entry removeMapping(Object o) { if (!(o instanceof Map.Entry)) return null; Map.Entry entry = (Map.Entry) o; Object key = entry.getKey(); int hash = (key == null) ? 0 : hash(key.hashCode()); int i = indexFor(hash, table.length); Entry prev = table[i]; Entry e = prev; while (e != null) { Entry 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) { 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; } 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 result = null; try { result = (HashMap)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 implements Map.Entry { final K key;//静态的值 V value; Entry next;//难道还有指针么？？ final int hash;//hash不可变 Entry(int h, K k, V v, Entry 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) {//两个的比较方法就是调用比较地址和equals 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(); } void recordAccess(HashMap m) { } void recordRemoval(HashMap m) { } } void addEntry(int hash, K key, V value, int bucketIndex) { Entry e = table[bucketIndex]; table[bucketIndex] = new Entry(hash, key, value, e); if (size++ >= threshold) resize(2 * table.length);//触发增加数组空间 } void createEntry(int hash, K key, V value, int bucketIndex) { Entry e = table[bucketIndex]; table[bucketIndex] = new Entry(hash, key, value, e); size++; } private abstract class HashIterator implements Iterator { Entry next; // next entry to return int expectedModCount; // For fast-fail int index; // current slot Entry 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 nextEntry() { if (modCount != expectedModCount) throw new ConcurrentModificationException(); Entry 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 { public V next() { return nextEntry().value; } } private final class KeyIterator extends HashIterator { public K next() { return nextEntry().getKey(); } } private final class EntryIterator extends HashIterator<Map.Entry> { public Map.Entry next() { return nextEntry(); } } // Subclass overrides these to alter behavior of views’ iterator() method Iterator newKeyIterator() { return new KeyIterator(); } Iterator newValueIterator() { return new ValueIterator(); } Iterator<Map.Entry> newEntryIterator() { return new EntryIterator(); } private transient Set<Map.Entry> entrySet = null; public Set keySet() { Set ks = keySet; return (ks != null ? ks : (keySet = new KeySet())); } private final class KeySet extends AbstractSet { public Iterator 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 values() { Collection vs = values; return (vs != null ? vs : (values = new Values())); } private final class Values extends AbstractCollection { public Iterator 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> entrySet() { return entrySet0(); } private Set<Map.Entry> entrySet0() { Set<Map.Entry> es = entrySet; return es != null ? es : (entrySet = new EntrySet()); } private final class EntrySet extends AbstractSet<Map.Entry> { public Iterator<Map.Entry> iterator() { return newEntryIterator(); } public boolean contains(Object o) { if (!(o instanceof Map.Entry)) return false; Map.Entry e = (Map.Entry) o; Entry 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> 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 (i != null) { while (i.hasNext()) { Map.Entry e = i.next(); s.writeObject(e.getKey()); s.writeObject(e.getValue()); } } } private static final long serialVersionUID = 362498820763181265L; /** * Reconstitute the HashMap instance from a stream (i.e., * deserialize it). */ 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); } } // These methods are used when serializing HashSets int capacity() { return table.length; } float loadFactor() { return loadFactor; } }

使用的是链表加hashcode 的混合，，稍微复杂一些，其实很多东西和学的差不多，，index 用的是位于其实就是mod吧，需要注意的就是增量因子，自己的容量，2的方最好否则会增加冲突的概率，还有就是Put比较hash的equals啊，hash相同产生冲突带来了不必要的开销要遍历整个链表，equals相同hashcode不同会放在不同的位置，，更加麻烦，，现实中尽量使hashcode和equals一样吧后面的博文来自转载，它告诉了我们whyhttp://beyond99.blog.51cto.com/1469451/429789