前言
HashMap數據結構由數組和鏈表(超過一定數量轉換爲紅黑樹)組成，在進行增刪查等操作時，首先要定位到元素的所在表的位置，之後再從鏈表中定位該元素。具體找到表下標的方法是(n - 1) & hash，其中n代表表的長度。
HashMap數據結構如下(確定下標用的是%取餘的方式)：
1 常量介紹
/**
* 默認容量16
* The default initial capacity - MUST be a power of two.
*/
static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16
/**
* 最大的容量
* 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;
/**
* 默認的負載因子
* The load factor used when none specified in constructor.
*/
static final float DEFAULT_LOAD_FACTOR = 0.75f;
/**
* 由鏈表轉換爲樹時桶的閾值,該值必須大於2，並且至少應該是8，以配合在樹移除結點收縮變回普通桶的假設
* The bin count threshold for using a tree rather than list for a
* bin. Bins are converted to trees when adding an element to a
* bin with at least this many nodes. The value must be greater
* than 2 and should be at least 8 to mesh with assumptions in
* tree removal about conversion back to plain bins upon
* shrinkage.
*/
static final int TREEIFY_THRESHOLD = 8;
/**
* 在resize操作中解除樹化的桶的最小閾值
* The bin count threshold for untreeifying a (split) bin during a
* resize operation. Should be less than TREEIFY_THRESHOLD, and at
* most 6 to mesh with shrinkage detection under removal.
*/
static final int UNTREEIFY_THRESHOLD = 6;
/**
* 桶樹化時table最小的容量(否則如果很多結點在桶中,table將進行擴容)(桶中的結點個數已經達到樹化的閾 * 值,但是table的容量沒有達到MIN_TREEIFY_CAPACITY,將進行擴容)
* The smallest table capacity for which bins may be treeified.
* (Otherwise the table is resized if too many nodes in a bin.)
* Should be at least 4 * TREEIFY_THRESHOLD to avoid conflicts
* between resizing and treeification thresholds.
*/
static final int MIN_TREEIFY_CAPACITY = 64;
/**
* table是使用的時候才初始化,需要的時候擴容.長度是2的冪指數(有事也是0)
* The table, initialized on first use, and resized as
* necessary. When allocated, length is always a power of two.
* (We also tolerate length zero in some operations to allow
* bootstrapping(引導) mechanics that are currently not needed.)
*/
transient Node<K,V>[] table;
/**
* Holds cached entrySet(). Note that AbstractMap fields are used
* for keySet() and values().
*/
transient Set<Map.Entry<K,V>> entrySet;
/**
* map中存儲的鍵值對數量
* The number of key-value mappings contained in this map.
*/
transient int size;
/**
* 改變hashMap中存儲的映射數量,或者改變HashMap的結構,值都會改變
* 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;
/**
* 進行擴容的閾值
* The next size value at which to resize (capacity * load factor).
*
* @serial
*/
// (The javadoc description is true upon serialization.
// Additionally, if the table array has not been allocated, this
// field holds the initial array capacity, or zero signifying
// DEFAULT_INITIAL_CAPACITY.)
int threshold;
/**
* 負載因子
* The load factor for the hash table.
*
* @serial
*/
final float loadFactor;
2 方法解析
2.1 構造方法
/**
* 使用默認初始化的容量16與負載因子
* Constructs an empty <tt>HashMap</tt> with the default initial capacity
* (16) and the default load factor (0.75).
*/
public HashMap() {
this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted
}
/**
* 使用指定初始化容量
* 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(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR);
}
/**
* 指定初始化容量和負載因子
* 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(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;
this.threshold = tableSizeFor(initialCapacity);
}
tableSizeFor
/**
* 得到大於n的2的整數次冪(對不規範的輸入進行處理)
* Returns a power of two size for the given target capacity.
*/
static final int tableSizeFor(int cap) {
//注意這裏-1操作
int n = cap - 1;
n |= n >>> 1;
n |= n >>> 2;
n |= n >>> 4;
n |= n >>> 8;
n |= n >>> 16;
return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
}
將n的二進制出現1的最高位後面所有位都實現置1(用4次或等(|=)運算實現)，最後+1得到大於n的整數次冪。因爲int類型爲32位，極限就是將32位全置爲1。
舉個栗子：
/**
* 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.loadFactor = DEFAULT_LOAD_FACTOR;
putMapEntries(m, false);
}
putMapEntries
/**
* Implements Map.putAll and Map constructor
*
* @param m the map
* @param evict false when initially constructing this map, else
* true (relayed to method afterNodeInsertion).
*/
final void putMapEntries(Map<? extends K, ? extends V> m, boolean evict) {
int s = m.size();
if (s > 0) {
//如果table爲空
if (table == null) { // pre-size
//計算容量是否超過最大容量
float ft = ((float)s / loadFactor) + 1.0F;
int t = ((ft < (float)MAXIMUM_CAPACITY) ?
(int)ft : MAXIMUM_CAPACITY);
if (t > threshold)
//得到大於等於t的2的整數次冪
threshold = tableSizeFor(t);
}
//如果不爲空且s>當前容量,擴容
else if (s > threshold)
resize();
//循環添加進相應的位置
for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) {
K key = e.getKey();
V value = e.getValue();
putVal(hash(key), key, value, false, evict);
}
}
}
2.2 常用方法
2.2.1 put(K,V)方法
/**
* 將指定值與此map中的指定鍵關聯,如果map中存在鍵,舊的值將被替換
* 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) {
return putVal(hash(key), key, value, false, true);
}
hash
/**
* 將高16位與低16位異或,目的是減少碰撞
* Computes key.hashCode() and spreads (XORs) higher bits of hash
* to lower. Because the table uses power-of-two masking, sets of
* hashes that vary only in bits above the current mask will
* always collide. (Among known examples are sets of Float keys
* holding consecutive whole numbers in small tables.) So we
* apply a transform that spreads the impact of higher bits
* downward. There is a tradeoff between speed, utility, and
* quality of bit-spreading. Because many common sets of hashes
* are already reasonably distributed (so don't benefit from
* spreading), and because we use trees to handle large sets of
* collisions in bins, we just XOR some shifted bits in the
* cheapest possible way to reduce systematic lossage, as well as
* to incorporate(合併) impact of the highest bits that would otherwise
* never be used in index calculations because of table bounds.
*/
static final int hash(Object key) {
int h;
return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}
putVal
/**
* Implements Map.put and related methods
*
* @param hash hash for key 鍵的hash值
* @param key the key 鍵
* @param value the value to put 值
* @param onlyIfAbsent if true, don't change existing value (爲真時，不會改變存在的值)
* @param evict if false, the table is in creation mode.(爲假時,創建模式)
* @return previous value(上一個值), or null if none
*/
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
boolean evict) {
Node<K,V>[] tab; Node<K,V> p; int n, i;
//如果是第一次，調用resize初始化
//如果table!=null(存在)，進行第二個條件判斷，將table的長度賦予n
if ((tab = table) == null || (n = tab.length) == 0)
n = (tab = resize()).length;
//注意算下標的方法：(n - 1) & hash
//如果相應下標下結點爲空，直接添加
if ((p = tab[i = (n - 1) & hash]) == null)
// Create a regular (non-tree) node 創建一個一般的非樹結點
tab[i] = newNode(hash, key, value, null);
//如果相應下標下結點不爲空
else {
Node<K,V> e; K k;
//如果hash相同,key相同
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
e = p;
//如果是紅黑樹結點
else if (p instanceof TreeNode)
e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
//如果是鏈表結點，hash相同,但是key不同
else {
for (int binCount = 0; ; ++binCount) {
//將新加入的結點加在鏈表末尾
if ((e = p.next) == null) {
p.next = newNode(hash, key, value, null);
//如果>=8-1,轉變爲紅黑樹
if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
treeifyBin(tab, hash);
break;
}
//如果hash相同，鍵相同
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
break;
p = e;
}
}
if (e != null) { // existing mapping for key 存在鍵相同的結點
V oldValue = e.value;
//如果爲true就不改變存在的值
if (!onlyIfAbsent || oldValue == null)
e.value = value;
afterNodeAccess(e);
return oldValue;
}
}
++modCount;
if (++size > threshold)
resize();
afterNodeInsertion(evict);
return null;
}
resize
/**
* 初始化或者加倍table的大小。如果爲null，分配初始化容量16，否則就加倍，每個元素的下標不變或者移動
* Initializes or doubles table size. If null, allocates in
* accord with initial capacity target held in field threshold.
* Otherwise, because we are using power-of-two expansion, the
* elements from each bin must either stay at same index, or move
* with a power of two offset in the new table.
*
* @return the table
*/
final Node<K,V>[] resize() {
//保存舊的（當前的）table
Node<K,V>[] oldTab = table;
//如果爲空，舊的容量爲0，否則就是原本table的長度
int oldCap = (oldTab == null) ? 0 : oldTab.length;
//保存舊的（當前的）閾值
int oldThr = threshold;
int newCap, newThr = 0;
//如果舊的容量大於0
if (oldCap > 0) {
//如果>=最大容量
if (oldCap >= MAXIMUM_CAPACITY) {
threshold = Integer.MAX_VALUE;
return oldTab;
}
//如果2*oldCap小於最大容量與oldCap>=16
else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
oldCap >= DEFAULT_INITIAL_CAPACITY)
newThr = oldThr << 1; // double threshold 加倍
}
//如果舊的閾值大於0
//不滿足上面的情況(初始化容量時<16)，將存儲在threshold中的值賦予newCap(容量)
else if (oldThr > 0) // initial capacity was placed in threshold
newCap = oldThr;
//容量<=0與閾值<=0,使用默認值初始化
else { // zero initial threshold signifies using defaults
newCap = DEFAULT_INITIAL_CAPACITY;
newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
}
if (newThr == 0) {
float ft = (float)newCap * loadFactor;
newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?
(int)ft : Integer.MAX_VALUE);
}
threshold = newThr;
@SuppressWarnings({"rawtypes","unchecked"})
Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
table = newTab;
//如果舊的table不爲空
if (oldTab != null) {
for (int j = 0; j < oldCap; ++j) {
Node<K,V> e;
if ((e = oldTab[j]) != null) {
//將舊值清空
oldTab[j] = null;
//next爲空，該位置只有一個結點(值)
if (e.next == null)
//重新根據hash與新的容量計算下標
newTab[e.hash & (newCap - 1)] = e;
//如果是樹結點
else if (e instanceof TreeNode)
//根據(e.hash & oldCap)分爲兩個，如果哪個數目不大於 //UNTREEIFY_THRESHOLD，就轉爲鏈表(與下面相同)
((TreeNode<K,V>)e).split(this, newTab, j, oldCap);
else { // preserve order
//分成低鏈表和高鏈表，分別指向頭與尾
Node<K,V> loHead = null, loTail = null;
Node<K,V> hiHead = null, hiTail = null;
Node<K,V> next;
//遍歷鏈表，根據e.hash & oldCap的值將同一桶中的元素分成兩個鏈表
do {
next = e.next;
//低鏈表，索引下標不變
if ((e.hash & oldCap) == 0) {
//第一次尾結點爲空，頭結點指向當前結點
if (loTail == null)
loHead = e;
//第二次及以後，將當前尾結點與當前結點連接起來
else
loTail.next = e;
//尾結點指向當前結點
loTail = e;
}
//高鏈表
else {
if (hiTail == null)
hiHead = e;
else
hiTail.next = e;
hiTail = e;
}
} while ((e = next) != null);
//將低鏈表的尾結點的next置爲null，替換原本索引下標下的鏈表
if (loTail != null) {
loTail.next = null;
newTab[j] = loHead;
}
//將高鏈表的尾結點的next置爲空，放在新的索引下標下
if (hiTail != null) {
hiTail.next = null;
newTab[j + oldCap] = hiHead;
}
}
}
}
}
return newTab;
}
分成的兩個高低鏈表索引下標是否變化,具體是要看原本hash值在新增加(擴容爲原來的2倍後,進位)的位上是0還是1，如果是0索引下標就不變(低鏈表)，如果是1索引下標就變化(原來的索引下標 + oldCap)。
原因：因爲表的容量是2的冪指數，原本的下標是通過hash&(容量-1)計算的。假設原本容量是8(0000,1000),hash值是19(0001,0011)。hash&(容量-1)[(0001,0011&0000,0111)]等於3。當容量變爲原來的兩倍時16(0001,0000),再次相與(0001,0011&0000,1111),值依然爲3(原因是hash指在容量新增加的位上是0，所以索引下標不變，反之增加的就是原本的舊容量)
treeifyBin
/**
* 替換指定哈希表的索引處的所有鏈接節點，除非表太小(未達到表的MIN_TREEIFY_CAPACITY 64)，否則將改 * 爲resize擴容操作
* Replaces all linked nodes in bin at index for given hash unless
* table is too small, in which case resizes instead.
*/
final void treeifyBin(Node<K,V>[] tab, int hash) {
int n, index; Node<K,V> e;
//如果tab爲null或者長度小於64,進行resize操作
if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY)
resize();
//下面的操作形成紅黑樹
else if ((e = tab[index = (n - 1) & hash]) != null) {
TreeNode<K,V> hd = null, tl = null;
do {
TreeNode<K,V> p = replacementTreeNode(e, null);
if (tl == null)
hd = p;
else {
p.prev = tl;
tl.next = p;
}
tl = p;
} while ((e = e.next) != null);
if ((tab[index] = hd) != null)
hd.treeify(tab);
}
}
2.2.2 get(Object)方法
/**
* 如果map中存在則返回指定鍵的值，如果不存在則返回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.)
*
* 返回null也可能是存在指定的key，但是value爲null，使用containsKey分辨
* <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) {
Node<K,V> e;
return (e = getNode(hash(key), key)) == null ? null : e.value;
}
getNode
/**
* Implements Map.get and related methods
*
* @param hash hash for key
* @param key the key
* @return the node, or null if none
*/
final Node<K,V> getNode(int hash, Object key) {
Node<K,V>[] tab; Node<K,V> first, e; int n; K k;
//如果table不爲空，長度>0，table中hash對應下標的第一個結點不爲null，有值
if ((tab = table) != null && (n = tab.length) > 0 &&
(first = tab[(n - 1) & hash]) != null) {
//第一個結點的hash和key都匹配，找到，返回
if (first.hash == hash && // always check first node
((k = first.key) == key || (key != null && key.equals(k))))
return first;
//第一個結點不匹配，且後面還存在結點，遍歷尋找
if ((e = first.next) != null) {
if (first instanceof TreeNode)
return ((TreeNode<K,V>)first).getTreeNode(hash, key);
do {
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
return e;
} while ((e = e.next) != null);
}
}
return null;
}
2.2.3 remove(Object)方法
/**
* 如果存在，則從此映射中刪除指定鍵的映射
* 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) {
Node<K,V> e;
return (e = removeNode(hash(key), key, null, false, true)) == null ?
null : e.value;
}
removeNode
/**
* Implements Map.remove and related methods
*
* @param hash hash for key
* @param key the key
* @param value the value to match if matchValue, else ignored
* @param matchValue if true only remove if value is equal
* @param movable if false do not move other nodes while removing
* @return the node, or null if none
*/
final Node<K,V> removeNode(int hash, Object key, Object value,
boolean matchValue, boolean movable) {
//p表示頭結點或者將要被刪除的結點的上一個結點
Node<K,V>[] tab; Node<K,V> p; int n, index;
//如果table不爲空，長度>0，table中hash對應下標的第一個結點不爲null，有值
if ((tab = table) != null && (n = tab.length) > 0 &&
(p = tab[index = (n - 1) & hash]) != null) {
//node指將要被刪除的結點
Node<K,V> node = null, e; K k; V v;
//與上面相同
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
node = p;
//鏈表頭結點不等，且後面還有結點
else if ((e = p.next) != null) {
//樹節點
if (p instanceof TreeNode)
node = ((TreeNode<K,V>)p).getTreeNode(hash, key);
else {
do {
if (e.hash == hash &&
((k = e.key) == key ||
(key != null && key.equals(k)))) {
//賦值給node
node = e;
break;
}
//賦值給p,方便後面操作
p = e;
} while ((e = e.next) != null);
}
}
if (node != null && (!matchValue || (v = node.value) == value ||
(value != null && value.equals(v)))) {
//如果是樹節點
if (node instanceof TreeNode)
((TreeNode<K,V>)node).removeTreeNode(this, tab, movable);
//如果頭結點是將要被刪除的結點
else if (node == p)
tab[index] = node.next;
else
p.next = node.next;
++modCount;
--size;
afterNodeRemoval(node);
return node;
}
}
return null;
}
2.2.4 keySet()方法
/**
* 返回包含在此map中的鍵的set視圖
* 如果在對集合進行迭代時修改了映射(除了通過迭代器自己的remove操作)，迭代的結果是未定義的(注意)
* Returns a {@link Set} view of the keys contained in this map.
* The set is backed by the map, so changes to the map are
* reflected in the set, and vice-versa. If the map is modified
* while an iteration over the set is in progress (except through
* the iterator's own <tt>remove</tt> operation), the results of
* the iteration are undefined. The set supports element removal,
* which removes the corresponding mapping from the map, via the
* <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
* operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
* operations.
*
* @return a set view of the keys contained in this map
*/
public Set<K> keySet() {
Set<K> ks = keySet;
//如果ks爲null,創建新的KeySet類
if (ks == null) {
ks = new KeySet();
keySet = ks;
}
return ks;
}
keySet類
final class KeySet extends AbstractSet<K> {
public final int size() { return size; }
public final void clear() { HashMap.this.clear(); }
public final Iterator<K> iterator() { return new KeyIterator(); }
public final boolean contains(Object o) { return containsKey(o); }
public final boolean remove(Object key) {
return removeNode(hash(key), key, null, false, true) != null;
}
public final Spliterator<K> spliterator() {
return new KeySpliterator<>(HashMap.this, 0, -1, 0, 0);
}
public final void forEach(Consumer<? super K> action) {
Node<K,V>[] tab;
if (action == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (int i = 0; i < tab.length; ++i) {
for (Node<K,V> e = tab[i]; e != null; e = e.next)
action.accept(e.key);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
}
2.2.5 entrySet()方法
/**
* 與上面相同
* Returns a {@link Set} view of the mappings contained in this map.
* The set is backed by the map, so changes to the map are
* reflected in the set, and vice-versa. If the map is modified
* while an iteration over the set is in progress (except through
* the iterator's own <tt>remove</tt> operation, or through the
* <tt>setValue</tt> operation on a map entry returned by the
* iterator) the results of the iteration are undefined. The set
* supports element removal, which removes the corresponding
* mapping from the map, via the <tt>Iterator.remove</tt>,
* <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
* <tt>clear</tt> operations. It does not support the
* <tt>add</tt> or <tt>addAll</tt> operations.
*
* @return a set view of the mappings contained in this map
*/
public Set<Map.Entry<K,V>> entrySet() {
Set<Map.Entry<K,V>> es;
return (es = entrySet) == null ? (entrySet = new EntrySet()) : es;
}
EntrySet類
final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
public final int size() { return size; }
public final void clear() { HashMap.this.clear(); }
//返回迭代對象
public final Iterator<Map.Entry<K,V>> iterator() {
return new EntryIterator();
}
//是否存在
public final boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry<?,?> e = (Map.Entry<?,?>) o;
Object key = e.getKey();
Node<K,V> candidate = getNode(hash(key), key);
//這裏的equals,當e爲Map.Entry時,比較鍵與值是否相同
return candidate != null && candidate.equals(e);
}
public final boolean remove(Object o) {
if (o instanceof Map.Entry) {
Map.Entry<?,?> e = (Map.Entry<?,?>) o;
Object key = e.getKey();
Object value = e.getValue();
return removeNode(hash(key), key, value, true, true) != null;
}
return false;
}
public final Spliterator<Map.Entry<K,V>> spliterator() {
return new EntrySpliterator<>(HashMap.this, 0, -1, 0, 0);
}
public final void forEach(Consumer<? super Map.Entry<K,V>> action) {
Node<K,V>[] tab;
if (action == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (int i = 0; i < tab.length; ++i) {
for (Node<K,V> e = tab[i]; e != null; e = e.next)
action.accept(e);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
}
2.2.6 values()方法
/**
* Returns a {@link Collection} view of the values contained in this map.
* The collection is backed by the map, so changes to the map are
* reflected in the collection, and vice-versa. If the map is
* modified while an iteration over the collection is in progress
* (except through the iterator's own <tt>remove</tt> operation),
* the results of the iteration are undefined. The collection
* supports element removal, which removes the corresponding
* mapping from the map, via the <tt>Iterator.remove</tt>,
* <tt>Collection.remove</tt>, <tt>removeAll</tt>,
* <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
* support the <tt>add</tt> or <tt>addAll</tt> operations.
*
* @return a view of the values contained in this map
*/
public Collection<V> values() {
Collection<V> vs = values;
if (vs == null) {
vs = new Values();
values = vs;
}
return vs;
}
Values類
final class Values extends AbstractCollection<V> {
public final int size() { return size; }
public final void clear() { HashMap.this.clear(); }
public final Iterator<V> iterator() { return new ValueIterator(); }
public final boolean contains(Object o) { return containsValue(o); }
public final Spliterator<V> spliterator() {
return new ValueSpliterator<>(HashMap.this, 0, -1, 0, 0);
}
public final void forEach(Consumer<? super V> action) {
Node<K,V>[] tab;
if (action == null)
throw new NullPointerException();
if (size > 0 && (tab = table) != null) {
int mc = modCount;
for (int i = 0; i < tab.length; ++i) {
for (Node<K,V> e = tab[i]; e != null; e = e.next)
action.accept(e.value);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
}
2.2.7 clear()方法
/**
* Removes all of the mappings from this map.
* The map will be empty after this call returns.
*/
public void clear() {
Node<K,V>[] tab;
modCount++;
if ((tab = table) != null && size > 0) {
//置0
size = 0;
//遍歷置空
for (int i = 0; i < tab.length; ++i)
tab[i] = null;
}
}