Java集合类---HashMap源码分析

JDK版本:1.8
package 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; } }

    原文作者:java集合源码分析
    原文地址: https://blog.csdn.net/xz10561/article/details/44136217
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