JDK8中的HashMap源码
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2022-06-05 17:33:29
背景 很久以前看过源码，但是猛一看总感觉挺难的，很少看下去。当时总感觉是水平不到。工作中也遇到一些想看源码的地方，但是遇到写的复杂些的心里就打退堂鼓了。 最近在接手同事的代码时，有一些很长的python脚本，没有一行注释。就硬着头皮一行一行的读，把理解的都加上注释，这样一行行看下来，终于知道代码的意 ......
背景
很久以前看过源码，但是猛一看总感觉挺难的，很少看下去。当时总感觉是水平不到。工作中也遇到一些想看源码的地方，但是遇到写的复杂些的心里就打退堂鼓了。
最近在接手同事的代码时，有一些很长的python脚本，没有一行注释。就硬着头皮一行一行的读，把理解的都加上注释，这样一行行看下来，终于知道代码的意思了。这对于我算是一种进步。
很久之前用了公司的一个分布式id生成的组件，该组件表明生成的id是增加的。但是实际使用过程中出现了id变小的情况，大致看了下代码，没有看懂。咨询了组件的负责人，负责人表示不会变小。前段时间，我就又硬着头皮一行行仔细看了好几遍，终于看明白了。对着之前异常id的日志，推理了一下代码流程，感觉会出现id变小的可能。于是在该组件的页面下面阐述了我的观点。（目前还没有回复，应该还没看到）现在快要过年了，手上的活没有那么紧了，所以趁机修炼内功，重新开始看jdk源码。
hashmap源码阅读
注释主要集中在get、put、resize三个方法上。
/*
* copyright (c) 1997, 2013, oracle and/or its affiliates. all rights reserved.
* oracle proprietary/confidential. use is subject to license terms.
*
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*/
package java.util;
import java.io.ioexception;
import java.io.invalidobjectexception;
import java.io.serializable;
import java.lang.reflect.parameterizedtype;
import java.lang.reflect.type;
import java.util.function.biconsumer;
import java.util.function.bifunction;
import java.util.function.consumer;
import java.util.function.function;
/**
* hash table based implementation of the <tt>map</tt> interface. this
* implementation provides all of the optional map operations, and permits
* <tt>null</tt> values and the <tt>null</tt> key. (the <tt>hashmap</tt>
* class is roughly equivalent to <tt>hashtable</tt>, except that it is
* unsynchronized and permits nulls.) this class makes no guarantees as to
* the order of the map; in particular, it does not guarantee that the order
* will remain constant over time.
*
* <p>this implementation provides constant-time performance for the basic
* operations (<tt>get</tt> and <tt>put</tt>), assuming the hash function
* disperses the elements properly among the buckets. iteration over
* collection views requires time proportional to the "capacity" of the
* <tt>hashmap</tt> instance (the number of buckets) plus its size (the number
* of key-value mappings). thus, it's very important not to set the initial
* capacity too high (or the load factor too low) if iteration performance is
* important.
*
* <p>an instance of <tt>hashmap</tt> has two parameters that affect its
* performance: <i>initial capacity</i> and <i>load factor</i>. the
* <i>capacity</i> is the number of buckets in the hash table, and the initial
* capacity is simply the capacity at the time the hash table is created. the
* <i>load factor</i> is a measure of how full the hash table is allowed to
* get before its capacity is automatically increased. when the number of
* entries in the hash table exceeds the product of the load factor and the
* current capacity, the hash table is <i>rehashed</i> (that is, internal data
* structures are rebuilt) so that the hash table has approximately twice the
* number of buckets.
*
* <p>as a general rule, the default load factor (.75) offers a good
* tradeoff between time and space costs. higher values decrease the
* space overhead but increase the lookup cost (reflected in most of
* the operations of the <tt>hashmap</tt> class, including
* <tt>get</tt> and <tt>put</tt>). the expected number of entries in
* the map and its load factor should be taken into account when
* setting its initial capacity, so as to minimize the number of
* rehash operations. if the initial capacity is greater than the
* maximum number of entries divided by the load factor, no rehash
* operations will ever occur.
*
* <p>if many mappings are to be stored in a <tt>hashmap</tt>
* instance, creating it with a sufficiently large capacity will allow
* the mappings to be stored more efficiently than letting it perform
* automatic rehashing as needed to grow the table. note that using
* many keys with the same {@code hashcode()} is a sure way to slow
* down performance of any hash table. to ameliorate impact, when keys
* are {@link comparable}, this class may use comparison order among
* keys to help break ties.
*
* <p><strong>note that this implementation is not synchronized.</strong>
* if multiple threads access a hash map concurrently, and at least one of
* the threads modifies the map structurally, it <i>must</i> be
* synchronized externally. (a structural modification is any operation
* that adds or deletes one or more mappings; merely changing the value
* associated with a key that an instance already contains is not a
* structural modification.) this is typically accomplished by
* synchronizing on some object that naturally encapsulates the map.
*
* if no such object exists, the map should be "wrapped" using the
* {@link collections#synchronizedmap collections.synchronizedmap}
* method. this is best done at creation time, to prevent accidental
* unsynchronized access to the map:<pre>
* map m = collections.synchronizedmap(new hashmap(...));</pre>
*
* <p>the iterators returned by all of this class's "collection view methods"
* are <i>fail-fast</i>: if the map is structurally modified at any time after
* the iterator is created, in any way except through the iterator's own
* <tt>remove</tt> method, the iterator will throw a
* {@link concurrentmodificationexception}. thus, in the face of concurrent
* modification, the iterator fails quickly and cleanly, rather than risking
* arbitrary, non-deterministic behavior at an undetermined time in the
* future.
*
* <p>note that the fail-fast behavior of an iterator cannot be guaranteed
* as it is, generally speaking, impossible to make any hard guarantees in the
* presence of unsynchronized concurrent modification. fail-fast iterators
* throw <tt>concurrentmodificationexception</tt> on a best-effort basis.
* therefore, it would be wrong to write a program that depended on this
* exception for its correctness: <i>the fail-fast behavior of iterators
* should be used only to detect bugs.</i>
*
* <p>this class is a member of the
* <a href="{@docroot}/../technotes/guides/collections/index.html">
* java collections framework</a>.
*
* @param <k> the type of keys maintained by this map
* @param <v> the type of mapped values
*
* @author doug lea
* @author josh bloch
* @author arthur van hoff
* @author neal gafter
* @see object#hashcode()
* @see collection
* @see map
* @see treemap
* @see hashtable
* @since 1.2
*/
public class hashmap<k,v> extends abstractmap<k,v>
implements map<k,v>, cloneable, serializable {
private static final long serialversionuid = 362498820763181265l;
/*
* implementation notes.
*
* this map usually acts as a binned (bucketed) hash table, but
* when bins get too large, they are transformed into bins of
* treenodes, each structured similarly to those in
* java.util.treemap. most methods try to use normal bins, but
* relay to treenode methods when applicable (simply by checking
* instanceof a node). bins of treenodes may be traversed and
* used like any others, but additionally support faster lookup
* when overpopulated. however, since the vast majority of bins in
* normal use are not overpopulated, checking for existence of
* tree bins may be delayed in the course of table methods.
*
* tree bins (i.e., bins whose elements are all treenodes) are
* ordered primarily by hashcode, but in the case of ties, if two
* elements are of the same "class c implements comparable<c>",
* type then their compareto method is used for ordering. (we
* conservatively check generic types via reflection to validate
* this -- see method comparableclassfor). the added complexity
* of tree bins is worthwhile in providing worst-case o(log n)
* operations when keys either have distinct hashes or are
* orderable, thus, performance degrades gracefully under
* accidental or malicious usages in which hashcode() methods
* return values that are poorly distributed, as well as those in
* which many keys share a hashcode, so long as they are also
* comparable. (if neither of these apply, we may waste about a
* factor of two in time and space compared to taking no
* precautions. but the only known cases stem from poor user
* programming practices that are already so slow that this makes
* little difference.)
*
* because treenodes are about twice the size of regular nodes, we
* use them only when bins contain enough nodes to warrant use
* (see treeify_threshold). and when they become too small (due to
* removal or resizing) they are converted back to plain bins. in
* usages with well-distributed user hashcodes, tree bins are
* rarely used. ideally, under random hashcodes, the frequency of
* nodes in bins follows a poisson distribution
* (http://en.wikipedia.org/wiki/poisson_distribution) with a
* parameter of about 0.5 on average for the default resizing
* threshold of 0.75, although with a large variance because of
* resizing granularity. ignoring variance, the expected
* occurrences of list size k are (exp(-0.5) * pow(0.5, k) /
* factorial(k)). the first values are:
*
* 0: 0.60653066
* 1: 0.30326533
* 2: 0.07581633
* 3: 0.01263606
* 4: 0.00157952
* 5: 0.00015795
* 6: 0.00001316
* 7: 0.00000094
* 8: 0.00000006
* more: less than 1 in ten million
*
* the root of a tree bin is normally its first node. however,
* sometimes (currently only upon iterator.remove), the root might
* be elsewhere, but can be recovered following parent links
* (method treenode.root()).
*
* all applicable internal methods accept a hash code as an
* argument (as normally supplied from a public method), allowing
* them to call each other without recomputing user hashcodes.
* most internal methods also accept a "tab" argument, that is
* normally the current table, but may be a new or old one when
* resizing or converting.
*
* when bin lists are treeified, split, or untreeified, we keep
* them in the same relative access/traversal order (i.e., field
* node.next) to better preserve locality, and to slightly
* simplify handling of splits and traversals that invoke
* iterator.remove. when using comparators on insertion, to keep a
* total ordering (or as close as is required here) across
* rebalancings, we compare classes and identityhashcodes as
* tie-breakers.
*
* the use and transitions among plain vs tree modes is
* complicated by the existence of subclass linkedhashmap. see
* below for hook methods defined to be invoked upon insertion,
* removal and access that allow linkedhashmap internals to
* otherwise remain independent of these mechanics. (this also
* requires that a map instance be passed to some utility methods
* that may create new nodes.)
*
* the concurrent-programming-like ssa-based coding style helps
* avoid aliasing errors amid all of the twisty pointer operations.
*/
/**
* the default initial capacity - must be a power of two.
*/
static final int default_initial_capacity = 1 << 4; // aka 16
/**
* 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;
/**
* the load factor used when none specified in constructor.
*/
static final float default_load_factor = 0.75f;
/**
* 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;
/**
* 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;
/**
* 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;
/**
* basic hash bin node, used for most entries. (see below for
* treenode subclass, and in linkedhashmap for its entry subclass.)
*/
static class node<k,v> implements map.entry<k,v> {
final int hash;
final k key;
v value;
node<k,v> next;
node(int hash, k key, v value, node<k,v> next) {
this.hash = hash;
this.key = key;
this.value = value;
this.next = next;
}
public final k getkey() { return key; }
public final v getvalue() { return value; }
public final string tostring() { return key + "=" + value; }
public final int hashcode() {
return objects.hashcode(key) ^ objects.hashcode(value);
}
public final v setvalue(v newvalue) {
v oldvalue = value;
value = newvalue;
return oldvalue;
}
public final boolean equals(object o) {
if (o == this)
return true;
if (o instanceof map.entry) {
map.entry<?,?> e = (map.entry<?,?>)o;
if (objects.equals(key, e.getkey()) &&
objects.equals(value, e.getvalue()))
return true;
}
return false;
}
}
/* ---------------- static utilities -------------- */
/**
* 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 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;
//取hash，为什么 先右移，然后进行与运算呢？
//https://www.cnblogs.com/wang-meng/p/9b6c35c4b2ef7e5b398db9211733292d.html
//上面说，这样运算有利于将hash打散，就是分散效果更好
return (key == null) ? 0 : (h = key.hashcode()) ^ (h >>> 16);
}
/**
* returns x's class if it is of the form "class c implements
* comparable<c>", else null.
*/
static class<?> comparableclassfor(object x) {
if (x instanceof comparable) {
class<?> c; type[] ts, as; type t; parameterizedtype p;
if ((c = x.getclass()) == string.class) // bypass checks
return c;
if ((ts = c.getgenericinterfaces()) != null) {
for (int i = 0; i < ts.length; ++i) {
if (((t = ts[i]) instanceof parameterizedtype) &&
((p = (parameterizedtype)t).getrawtype() ==
comparable.class) &&
(as = p.getactualtypearguments()) != null &&
as.length == 1 && as[0] == c) // type arg is c
return c;
}
}
}
return null;
}
/**
* returns k.compareto(x) if x matches kc (k's screened comparable
* class), else 0.
*/
@suppresswarnings({"rawtypes","unchecked"}) // for cast to comparable
static int comparecomparables(class<?> kc, object k, object x) {
return (x == null || x.getclass() != kc ? 0 :
((comparable)k).compareto(x));
}
/**
* returns a power of two size for the given target capacity.
*/
static final int tablesizefor(int cap) {
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;
}
/* ---------------- fields -------------- */
/**
* 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 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;
/**
* the number of key-value mappings contained in this map.
*/
transient int size;
/**
* 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;
/**
* 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;
/**
* the load factor for the hash table.
*
* @serial
*/
final float loadfactor;
/* ---------------- public operations -------------- */
/**
* 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);
}
/**
* 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);
}
/**
* 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
}
/**
* 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);
}
/**
* 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) {
if (table == null) { // pre-size
float ft = ((float)s / loadfactor) + 1.0f;
int t = ((ft < (float)maximum_capacity) ?
(int)ft : maximum_capacity);
if (t > threshold)
threshold = tablesizefor(t);
}
else if (s > threshold)
resize();
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);
}
}
}
/**
* returns the number of key-value mappings in this map.
*
* @return the number of key-value mappings in this map
*/
public int size() {
return size;
}
/**
* returns <tt>true</tt> if this map contains no key-value mappings.
*
* @return <tt>true</tt> if this map contains no key-value mappings
*/
public boolean isempty() {
return size == 0;
}
/**
* 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) {
node<k,v> e;
return (e = getnode(hash(key), key)) == null ? null : e.value;
}
/**
* implements map.get and related methods
* 获取节点
* @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;
//表不为null，且长度>0，且hash槽不为null
if ((tab = table) != null && (n = tab.length) > 0 &&
(first = tab[(n - 1) & hash]) != null) {
//先比较第1个，first已经在if里赋值了
if (first.hash == hash && // always check first node
((k = first.key) == key || (key != null && key.equals(k))))
return first;
//有第2个
if ((e = first.next) != null) {
if (first instanceof treenode)//treenode类型，进行二叉树查找
return ((treenode<k,v>)first).gettreenode(hash, key);
do {//遍历，比较
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
return e;
} while ((e = e.next) != null);
}
}
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 getnode(hash(key), key) != null;
}
/**
* 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);
}
/**
* implements map.put and related methods
*
* @param hash hash for key
* @param key the key
* @param value the value to put
* @param onlyifabsent if true, don't change existing value
* @param evict if false, the table is in creation mode.
* @return previous value, 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;
//tab为空，或者长度是0，就进行扩容
if ((tab = table) == null || (n = tab.length) == 0)
n = (tab = resize()).length;
//如果hash处为空，就直接在该处赋值
if ((p = tab[i = (n - 1) & hash]) == null)
tab[i] = newnode(hash, key, value, null);
else {
node<k,v> e; k k;
//比较第一个值
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
e = p;
else if (p instanceof treenode) //如果是treenode类型，就调用treenode的添加方法
e = ((treenode<k,v>)p).puttreeval(this, tab, hash, key, value);
else {
for (int bincount = 0; ; ++bincount) {
//p的next是空，添加值，并结束
if ((e = p.next) == null) {
//赋值next
p.next = newnode(hash, key, value, null);
//如果计算超过8个，就转为二叉树结构
if (bincount >= treeify_threshold - 1) // -1 for 1st
treeifybin(tab, hash);
break;
}
//前面已经对e赋过值
//如果当前节点比对成功，就结束
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
break;
//对p赋值，进行下一轮循环
p = e;
}
}
//key存在，替换旧值
if (e != null) { // existing mapping for key
v oldvalue = e.value;
if (!onlyifabsent || oldvalue == null)
e.value = value;
afternodeaccess(e);
//返回旧值
return oldvalue;
}
}
++modcount;
//判断是否需要扩容
if (++size > threshold)
resize();
afternodeinsertion(evict);
return null;
}
/**
* 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() {
node<k,v>[] oldtab = table;
int oldcap = (oldtab == null) ? 0 : oldtab.length;
int oldthr = threshold;
int newcap, newthr = 0;
if (oldcap > 0) {
if (oldcap >= maximum_capacity) {
threshold = integer.max_value;
return oldtab;
}
else if ((newcap = oldcap << 1) < maximum_capacity &&
oldcap >= default_initial_capacity)
newthr = oldthr << 1; // double threshold
}
else if (oldthr > 0) // initial capacity was placed in threshold
newcap = oldthr;
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;
//定义新tab
@suppresswarnings({"rawtypes","unchecked"})
node<k,v>[] newtab = (node<k,v>[])new node[newcap];
table = newtab;
//迁移kv
if (oldtab != null) {
for (int j = 0; j < oldcap; ++j) {
node<k,v> e;
if ((e = oldtab[j]) != null) {
oldtab[j] = null;
//e没有下一个，直接hash赋值
if (e.next == null)
newtab[e.hash & (newcap - 1)] = e;
else if (e instanceof treenode)
((treenode<k,v>)e).split(this, newtab, j, oldcap);
else { // preserve order
node<k,v> lohead = null, lotail = null;
node<k,v> hihead = null, hitail = null;
node<k,v> next;
//此处参考：https://www.cnblogs.com/williamjie/p/9358291.html
//找到待迁移元素和该元素的上游
do {
next = e.next;
//与运算后值不变，说明后续的位置不变
if ((e.hash & oldcap) == 0) {
if (lotail == null)
lohead = e;
else
lotail.next = e;
lotail = e;
}
else {//位置需要加上oldcap
if (hitail == null)
hihead = e;
else
hitail.next = e;
hitail = e;
}
} while ((e = next) != null);
//断除旧节点连接，赋新值
if (lotail != null) {
lotail.next = null;
newtab[j] = lohead;
}
if (hitail != null) {
hitail.next = null;
newtab[j + oldcap] = hihead;
}
}
}
}
}
return newtab;
}
/**
* 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;
if (tab == null || (n = tab.length) < min_treeify_capacity)
resize();
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);
}
}
/**
* 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) {
putmapentries(m, true);
}
/**
* 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;
}
/**
* 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) {
node<k,v>[] tab; node<k,v> p; int n, index;
if ((tab = table) != null && (n = tab.length) > 0 &&
(p = tab[index = (n - 1) & hash]) != null) {
node<k,v> node = null, e; k k; v v;
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
node = p;
else if ((e = p.next) != null) {
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)))) {
node = e;
break;
}
p = e;
} while ((e = e.next) != null);
}
}
if (node != null && (!matchvalue || (v = node.value) == value ||
(value != null && value.equals(v)))) {
if (node instanceof treenode)
((treenode<k,v>)node).removetreenode(this, tab, movable);
else if (node == p)
tab[index] = node.next;
else
p.next = node.next;
++modcount;
--size;
afternoderemoval(node);
return node;
}
}
return null;
}
/**
* 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) {
size = 0;
for (int i = 0; i < tab.length; ++i)
tab[i] = null;
}
}
/**
* 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) {
node<k,v>[] tab; v v;
if ((tab = table) != null && size > 0) {
for (int i = 0; i < tab.length; ++i) {
for (node<k,v> e = tab[i]; e != null; e = e.next) {
if ((v = e.value) == value ||
(value != null && value.equals(v)))
return true;
}
}
}
return false;
}
/**
* 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;
if (ks == null) {
ks = new keyset();
keyset = ks;
}
return ks;
}
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();
}
}
}
/**
* 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;
}
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();
}
}
}
/**
* 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;
}
final class entryset extends abstractset<map.entry<k,v>> {
public final int size() { return size; }
public final void clear() { hashmap.this.clear(); }
public final iterator<map.entry<k,v>> iterator() {
return new entryiterator();
}
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);
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();
}
}
}
// overrides of jdk8 map extension methods
@override
public v getordefault(object key, v defaultvalue) {
node<k,v> e;
return (e = getnode(hash(key), key)) == null ? defaultvalue : e.value;
}
@override
public v putifabsent(k key, v value) {
return putval(hash(key), key, value, true, true);
}
@override
public boolean remove(object key, object value) {
return removenode(hash(key), key, value, true, true) != null;
}
@override
public boolean replace(k key, v oldvalue, v newvalue) {
node<k,v> e; v v;
if ((e = getnode(hash(key), key)) != null &&
((v = e.value) == oldvalue || (v != null && v.equals(oldvalue)))) {
e.value = newvalue;
afternodeaccess(e);
return true;
}
return false;
}
@override
public v replace(k key, v value) {
node<k,v> e;
if ((e = getnode(hash(key), key)) != null) {
v oldvalue = e.value;
e.value = value;
afternodeaccess(e);
return oldvalue;
}
return null;
}
@override
public v computeifabsent(k key,
function<? super k, ? extends v> mappingfunction) {
if (mappingfunction == null)
throw new nullpointerexception();
int hash = hash(key);
node<k,v>[] tab; node<k,v> first; int n, i;
int bincount = 0;
treenode<k,v> t = null;
node<k,v> old = null;
if (size > threshold || (tab = table) == null ||
(n = tab.length) == 0)
n = (tab = resize()).length;
if ((first = tab[i = (n - 1) & hash]) != null) {
if (first instanceof treenode)
old = (t = (treenode<k,v>)first).gettreenode(hash, key);
else {
node<k,v> e = first; k k;
do {
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k)))) {
old = e;
break;
}
++bincount;
} while ((e = e.next) != null);
}
v oldvalue;
if (old != null && (oldvalue = old.value) != null) {
afternodeaccess(old);
return oldvalue;
}
}
v v = mappingfunction.apply(key);
if (v == null) {
return null;
} else if (old != null) {
old.value = v;
afternodeaccess(old);
return v;
}
else if (t != null)
t.puttreeval(this, tab, hash, key, v);
else {
tab[i] = newnode(hash, key, v, first);
if (bincount >= treeify_threshold - 1)
treeifybin(tab, hash);
}
++modcount;
++size;
afternodeinsertion(true);
return v;
}
public v computeifpresent(k key,
bifunction<? super k, ? super v, ? extends v> remappingfunction) {
if (remappingfunction == null)
throw new nullpointerexception();
node<k,v> e; v oldvalue;
int hash = hash(key);
if ((e = getnode(hash, key)) != null &&
(oldvalue = e.value) != null) {
v v = remappingfunction.apply(key, oldvalue);
if (v != null) {
e.value = v;
afternodeaccess(e);
return v;
}
else
removenode(hash, key, null, false, true);
}
return null;
}
@override
public v compute(k key,
bifunction<? super k, ? super v, ? extends v> remappingfunction) {
if (remappingfunction == null)
throw new nullpointerexception();
int hash = hash(key);
node<k,v>[] tab; node<k,v> first; int n, i;
int bincount = 0;
treenode<k,v> t = null;
node<k,v> old = null;
if (size > threshold || (tab = table) == null ||
(n = tab.length) == 0)
n = (tab = resize()).length;
if ((first = tab[i = (n - 1) & hash]) != null) {
if (first instanceof treenode)
old = (t = (treenode<k,v>)first).gettreenode(hash, key);
else {
node<k,v> e = first; k k;
do {
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k)))) {
old = e;
break;
}
++bincount;
} while ((e = e.next) != null);
}
}
v oldvalue = (old == null) ? null : old.value;
v v = remappingfunction.apply(key, oldvalue);
if (old != null) {
if (v != null) {
old.value = v;
afternodeaccess(old);
}
else
removenode(hash, key, null, false, true);
}
else if (v != null) {
if (t != null)
t.puttreeval(this, tab, hash, key, v);
else {
tab[i] = newnode(hash, key, v, first);
if (bincount >= treeify_threshold - 1)
treeifybin(tab, hash);
}
++modcount;
++size;
afternodeinsertion(true);
}
return v;
}
@override
public v merge(k key, v value,
bifunction<? super v, ? super v, ? extends v> remappingfunction) {
if (value == null)
throw new nullpointerexception();
if (remappingfunction == null)
throw new nullpointerexception();
int hash = hash(key);
node<k,v>[] tab; node<k,v> first; int n, i;
int bincount = 0;
treenode<k,v> t = null;
node<k,v> old = null;
if (size > threshold || (tab = table) == null ||
(n = tab.length) == 0)
n = (tab = resize()).length;
if ((first = tab[i = (n - 1) & hash]) != null) {
if (first instanceof treenode)
old = (t = (treenode<k,v>)first).gettreenode(hash, key);
else {
node<k,v> e = first; k k;
do {
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k)))) {
old = e;
break;
}
++bincount;
} while ((e = e.next) != null);
}
}
if (old != null) {
v v;
if (old.value != null)
v = remappingfunction.apply(old.value, value);
else
v = value;
if (v != null) {
old.value = v;
afternodeaccess(old);
}
else
removenode(hash, key, null, false, true);
return v;
}
if (value != null) {
if (t != null)
t.puttreeval(this, tab, hash, key, value);
else {
tab[i] = newnode(hash, key, value, first);
if (bincount >= treeify_threshold - 1)
treeifybin(tab, hash);
}
++modcount;
++size;
afternodeinsertion(true);
}
return value;
}
@override
public void foreach(biconsumer<? super k, ? 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.key, e.value);
}
if (modcount != mc)
throw new concurrentmodificationexception();
}
}
@override
public void replaceall(bifunction<? super k, ? super v, ? extends v> function) {
node<k,v>[] tab;
if (function == 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) {
e.value = function.apply(e.key, e.value);
}
}
if (modcount != mc)
throw new concurrentmodificationexception();
}
}
/* ------------------------------------------------------------ */
// cloning and serialization
/**
* 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
*/
@suppresswarnings("unchecked")
@override
public object clone() {
hashmap<k,v> result;
try {
result = (hashmap<k,v>)super.clone();
} catch (clonenotsupportedexception e) {
// this shouldn't happen, since we are cloneable
throw new internalerror(e);
}
result.reinitialize();
result.putmapentries(this, false);
return result;
}
// these methods are also used when serializing hashsets
final float loadfactor() { return loadfactor; }
final int capacity() {
return (table != null) ? table.length :
(threshold > 0) ? threshold :
default_initial_capacity;
}
/**
* save the state of the <tt>hashmap</tt> instance to a stream (i.e.,
* serialize it).
*
* @serialdata the <i>capacity</i> of the hashmap (the length of the
* bucket array) is emitted (int), followed by the
* <i>size</i> (an int, the number of key-value
* mappings), followed by the key (object) and value (object)
* for each key-value mapping. the key-value mappings are
* emitted in no particular order.
*/
private void writeobject(java.io.objectoutputstream s)
throws ioexception {
int buckets = capacity();
// write out the threshold, loadfactor, and any hidden stuff
s.defaultwriteobject();
s.writeint(buckets);
s.writeint(size);
internalwriteentries(s);
}
/**
* reconstitute the {@code hashmap} instance from a stream (i.e.,
* deserialize it).
*/
private void readobject(java.io.objectinputstream s)
throws ioexception, classnotfoundexception {
// read in the threshold (ignored), loadfactor, and any hidden stuff
s.defaultreadobject();
reinitialize();
if (loadfactor <= 0 || float.isnan(loadfactor))
throw new invalidobjectexception("illegal load factor: " +
loadfactor);
s.readint(); // read and ignore number of buckets
int mappings = s.readint(); // read number of mappings (size)
if (mappings < 0)
throw new invalidobjectexception("illegal mappings count: " +
mappings);
else if (mappings > 0) { // (if zero, use defaults)
// size the table using given load factor only if within
// range of 0.25...4.0
float lf = math.min(math.max(0.25f, loadfactor), 4.0f);
float fc = (float)mappings / lf + 1.0f;
int cap = ((fc < default_initial_capacity) ?
default_initial_capacity :
(fc >= maximum_capacity) ?
maximum_capacity :
tablesizefor((int)fc));
float ft = (float)cap * lf;
threshold = ((cap < maximum_capacity && ft < maximum_capacity) ?
(int)ft : integer.max_value);
@suppresswarnings({"rawtypes","unchecked"})
node<k,v>[] tab = (node<k,v>[])new node[cap];
table = tab;
// read the keys and values, and put the mappings in the hashmap
for (int i = 0; i < mappings; i++) {
@suppresswarnings("unchecked")
k key = (k) s.readobject();
@suppresswarnings("unchecked")
v value = (v) s.readobject();
putval(hash(key), key, value, false, false);
}
}
}
/* ------------------------------------------------------------ */
// iterators
abstract class hashiterator {
node<k,v> next; // next entry to return
node<k,v> current; // current entry
int expectedmodcount; // for fast-fail
int index; // current slot
hashiterator() {
expectedmodcount = modcount;
node<k,v>[] t = table;
current = next = null;
index = 0;
if (t != null && size > 0) { // advance to first entry
do {} while (index < t.length && (next = t[index++]) == null);
}
}
public final boolean hasnext() {
return next != null;
}
final node<k,v> nextnode() {
node<k,v>[] t;
node<k,v> e = next;
if (modcount != expectedmodcount)
throw new concurrentmodificationexception();
if (e == null)
throw new nosuchelementexception();
if ((next = (current = e).next) == null && (t = table) != null) {
do {} while (index < t.length && (next = t[index++]) == null);
}
return e;
}
public final void remove() {
node<k,v> p = current;
if (p == null)
throw new illegalstateexception();
if (modcount != expectedmodcount)
throw new concurrentmodificationexception();
current = null;
k key = p.key;
removenode(hash(key), key, null, false, false);
expectedmodcount = modcount;
}
}
final class keyiterator extends hashiterator
implements iterator<k> {
public final k next() { return nextnode().key; }
}
final class valueiterator extends hashiterator
implements iterator<v> {
public final v next() { return nextnode().value; }
}
final class entryiterator extends hashiterator
implements iterator<map.entry<k,v>> {
public final map.entry<k,v> next() { return nextnode(); }
}
/* ------------------------------------------------------------ */
// spliterators
static class hashmapspliterator<k,v> {
final hashmap<k,v> map;
node<k,v> current; // current node
int index; // current index, modified on advance/split
int fence; // one past last index
int est; // size estimate
int expectedmodcount; // for comodification checks
hashmapspliterator(hashmap<k,v> m, int origin,
int fence, int est,
int expectedmodcount) {
this.map = m;
this.index = origin;
this.fence = fence;
this.est = est;
this.expectedmodcount = expectedmodcount;
}
final int getfence() { // initialize fence and size on first use
int hi;
if ((hi = fence) < 0) {
hashmap<k,v> m = map;
est = m.size;
expectedmodcount = m.modcount;
node<k,v>[] tab = m.table;
hi = fence = (tab == null) ? 0 : tab.length;
}
return hi;
}
public final long estimatesize() {
getfence(); // force init
return (long) est;
}
}
static final class keyspliterator<k,v>
extends hashmapspliterator<k,v>
implements spliterator<k> {
keyspliterator(hashmap<k,v> m, int origin, int fence, int est,
int expectedmodcount) {
super(m, origin, fence, est, expectedmodcount);
}
public keyspliterator<k,v> trysplit() {
int hi = getfence(), lo = index, mid = (lo + hi) >>> 1;
return (lo >= mid || current != null) ? null :
new keyspliterator<>(map, lo, index = mid, est >>>= 1,
expectedmodcount);
}
public void foreachremaining(consumer<? super k> action) {
int i, hi, mc;
if (action == null)
throw new nullpointerexception();
hashmap<k,v> m = map;
node<k,v>[] tab = m.table;
if ((hi = fence) < 0) {
mc = expectedmodcount = m.modcount;
hi = fence = (tab == null) ? 0 : tab.length;
}
else
mc = expectedmodcount;
if (tab != null && tab.length >= hi &&
(i = index) >= 0 && (i < (index = hi) || current != null)) {
node<k,v> p = current;
current = null;
do {
if (p == null)
p = tab[i++];
else {
action.accept(p.key);
p = p.next;
}
} while (p != null || i < hi);
if (m.modcount != mc)
throw new concurrentmodificationexception();
}
}
public boolean tryadvance(consumer<? super k> action) {
int hi;
if (action == null)
throw new nullpointerexception();
node<k,v>[] tab = map.table;
if (tab != null && tab.length >= (hi = getfence()) && index >= 0) {
while (current != null || index < hi) {
if (current == null)
current = tab[index++];
else {
k k = current.key;
current = current.next;
action.accept(k);
if (map.modcount != expectedmodcount)
throw new concurrentmodificationexception();
return true;
}
}
}
return false;
}
public int characteristics() {
return (fence < 0 || est == map.size ? spliterator.sized : 0) |
spliterator.distinct;
}
}
static final class valuespliterator<k,v>
extends hashmapspliterator<k,v>
implements spliterator<v> {
valuespliterator(hashmap<k,v> m, int origin, int fence, int est,
int expectedmodcount) {
super(m, origin, fence, est, expectedmodcount);
}
public valuespliterator<k,v> trysplit() {
int hi = getfence(), lo = index, mid = (lo + hi) >>> 1;
return (lo >= mid || current != null) ? null :
new valuespliterator<>(map, lo, index = mid, est >>>= 1,
expectedmodcount);
}
public void foreachremaining(consumer<? super v> action) {
int i, hi, mc;
if (action == null)
throw new nullpointerexception();
hashmap<k,v> m = map;
node<k,v>[] tab = m.table;
if ((hi = fence) < 0) {
mc = expectedmodcount = m.modcount;
hi = fence = (tab == null) ? 0 : tab.length;
}
else
mc = expectedmodcount;
if (tab != null && tab.length >= hi &&
(i = index) >= 0 && (i < (index = hi) || current != null)) {
node<k,v> p = current;
current = null;
do {
if (p == null)
p = tab[i++];
else {
action.accept(p.value);
p = p.next;
}
} while (p != null || i < hi);
if (m.modcount != mc)
throw new concurrentmodificationexception();
}
}
public boolean tryadvance(consumer<? super v> action) {
int hi;
if (action == null)
throw new nullpointerexception();
node<k,v>[] tab = map.table;
if (tab != null && tab.length >= (hi = getfence()) && index >= 0) {
while (current != null || index < hi) {
if (current == null)
current = tab[index++];
else {
v v = current.value;
current = current.next;
action.accept(v);
if (map.modcount != expectedmodcount)
throw new concurrentmodificationexception();
return true;
}
}
}
return false;
}
public int characteristics() {
return (fence < 0 || est == map.size ? spliterator.sized : 0);
}
}
static final class entryspliterator<k,v>
extends hashmapspliterator<k,v>
implements spliterator<map.entry<k,v>> {
entryspliterator(hashmap<k,v> m, int origin, int fence, int est,
int expectedmodcount) {
super(m, origin, fence, est, expectedmodcount);
}
public entryspliterator<k,v> trysplit() {
int hi = getfence(), lo = index, mid = (lo + hi) >>> 1;
return (lo >= mid || current != null) ? null :
new entryspliterator<>(map, lo, index = mid, est >>>= 1,
expectedmodcount);
}
public void foreachremaining(consumer<? super map.entry<k,v>> action) {
int i, hi, mc;
if (action == null)
throw new nullpointerexception();
hashmap<k,v> m = map;
node<k,v>[] tab = m.table;
if ((hi = fence) < 0) {
mc = expectedmodcount = m.modcount;
hi = fence = (tab == null) ? 0 : tab.length;
}
else
mc = expectedmodcount;
if (tab != null && tab.length >= hi &&
(i = index) >= 0 && (i < (index = hi) || current != null)) {
node<k,v> p = current;
current = null;
do {
if (p == null)
p = tab[i++];
else {
action.accept(p);
p = p.next;
}
} while (p != null || i < hi);
if (m.modcount != mc)
throw new concurrentmodificationexception();
}
}
public boolean tryadvance(consumer<? super map.entry<k,v>> action) {
int hi;
if (action == null)
throw new nullpointerexception();
node<k,v>[] tab = map.table;
if (tab != null && tab.length >= (hi = getfence()) && index >= 0) {
while (current != null || index < hi) {
if (current == null)
current = tab[index++];
else {
node<k,v> e = current;
current = current.next;
action.accept(e);
if (map.modcount != expectedmodcount)
throw new concurrentmodificationexception();
return true;
}
}
}
return false;
}
public int characteristics() {
return (fence < 0 || est == map.size ? spliterator.sized : 0) |
spliterator.distinct;
}
}
/* ------------------------------------------------------------ */
// linkedhashmap support
/*
* the following package-protected methods are designed to be
* overridden by linkedhashmap, but not by any other subclass.
* nearly all other internal methods are also package-protected
* but are declared final, so can be used by linkedhashmap, view
* classes, and hashset.
*/
// create a regular (non-tree) node
node<k,v> newnode(int hash, k key, v value, node<k,v> next) {
return new node<>(hash, key, value, next);
}
// for conversion from treenodes to plain nodes
node<k,v> replacementnode(node<k,v> p, node<k,v> next) {
return new node<>(p.hash, p.key, p.value, next);
}
// create a tree bin node
treenode<k,v> newtreenode(int hash, k key, v value, node<k,v> next) {
return new treenode<>(hash, key, value, next);
}
// for treeifybin
treenode<k,v> replacementtreenode(node<k,v> p, node<k,v> next) {
return new treenode<>(p.hash, p.key, p.value, next);
}
/**
* reset to initial default state. called by clone and readobject.
*/
void reinitialize() {
table = null;
entryset = null;
keyset = null;
values = null;
modcount = 0;
threshold = 0;
size = 0;
}
// callbacks to allow linkedhashmap post-actions
void afternodeaccess(node<k,v> p) { }
void afternodeinsertion(boolean evict) { }
void afternoderemoval(node<k,v> p) { }
// called only from writeobject, to ensure compatible ordering.
void internalwriteentries(java.io.objectoutputstream s) throws ioexception {
node<k,v>[] tab;
if (size > 0 && (tab = table) != null) {
for (int i = 0; i < tab.length; ++i) {
for (node<k,v> e = tab[i]; e != null; e = e.next) {
s.writeobject(e.key);
s.writeobject(e.value);
}
}
}
}
/* ------------------------------------------------------------ */
// tree bins
/**
* entry for tree bins. extends linkedhashmap.entry (which in turn
* extends node) so can be used as extension of either regular or
* linked node.
*/
static final class treenode<k,v> extends linkedhashmap.entry<k,v> {
treenode<k,v> parent; // red-black tree links
treenode<k,v> left;
treenode<k,v> right;
treenode<k,v> prev; // needed to unlink next upon deletion
boolean red;
treenode(int hash, k key, v val, node<k,v> next) {
super(hash, key, val, next);
}
/**
* returns root of tree containing this node.
*/
final treenode<k,v> root() {
for (treenode<k,v> r = this, p;;) {
if ((p = r.parent) == null)
return r;
r = p;
}
}
/**
* ensures that the given root is the first node of its bin.
*/
static <k,v> void moveroottofront(node<k,v>[] tab, treenode<k,v> root) {
int n;
if (root != null && tab != null && (n = tab.length) > 0) {
int index = (n - 1) & root.hash;
treenode<k,v> first = (treenode<k,v>)tab[index];
if (root != first) {
node<k,v> rn;
tab[index] = root;
treenode<k,v> rp = root.prev;
if ((rn = root.next) != null)
((treenode<k,v>)rn).prev = rp;
if (rp != null)
rp.next = rn;
if (first != null)
first.prev = root;
root.next = first;
root.prev = null;
}
assert checkinvariants(root);
}
}
/**
* finds the node starting at root p with the given hash and key.
* the kc argument caches comparableclassfor(key) upon first use
* comparing keys.
*/
final treenode<k,v> find(int h, object k, class<?> kc) {
treenode<k,v> p = this;
do {
int ph, dir; k pk;
treenode<k,v> pl = p.left, pr = p.right, q;
if ((ph = p.hash) > h)
p = pl;
else if (ph < h)
p = pr;
else if ((pk = p.key) == k || (k != null && k.equals(pk)))
return p;
else if (pl == null)
p = pr;
else if (pr == null)
p = pl;
else if ((kc != null ||
(kc = comparableclassfor(k)) != null) &&
(dir = comparecomparables(kc, k, pk)) != 0)
p = (dir < 0) ? pl : pr;
else if ((q = pr.find(h, k, kc)) != null)
return q;
else
p = pl;
} while (p != null);
return null;
}
/**
* calls find for root node.
*/
final treenode<k,v> gettreenode(int h, object k) {
return ((parent != null) ? root() : this).find(h, k, null);
}
/**
* tie-breaking utility for ordering insertions when equal
* hashcodes and non-comparable. we don't require a total
* order, just a consistent insertion rule to maintain
* equivalence across rebalancings. tie-breaking further than
* necessary simplifies testing a bit.
*/
static int tiebreakorder(object a, object b) {
int d;
if (a == null || b == null ||
(d = a.getclass().getname().
compareto(b.getclass().getname())) == 0)
d = (system.identityhashcode(a) <= system.identityhashcode(b) ?
-1 : 1);
return d;
}
/**
* forms tree of the nodes linked from this node.
* @return root of tree
*/
final void treeify(node<k,v>[] tab) {
treenode<k,v> root = null;
for (treenode<k,v> x = this, next; x != null; x = next) {
next = (treenode<k,v>)x.next;
x.left = x.right = null;
if (root == null) {
x.parent = null;
x.red = false;
root = x;
}
else {
k k = x.key;
int h = x.hash;
class<?> kc = null;
for (treenode<k,v> p = root;;) {
int dir, ph;
k pk = p.key;
if ((ph = p.hash) > h)
dir = -1;
else if (ph < h)
dir = 1;
else if ((kc == null &&
(kc = comparableclassfor(k)) == null) ||
(dir = comparecomparables(kc, k, pk)) == 0)
dir = tiebreakorder(k, pk);
treenode<k,v> xp = p;
if ((p = (dir <= 0) ? p.left : p.right) == null) {
x.parent = xp;
if (dir <= 0)
xp.left = x;
else
xp.right = x;
root = balanceinsertion(root, x);
break;
}
}
}
}
moveroottofront(tab, root);
}
/**
* returns a list of non-treenodes replacing those linked from
* this node.
*/
final node<k,v> untreeify(hashmap<k,v> map) {
node<k,v> hd = null, tl = null;
for (node<k,v> q = this; q != null; q = q.next) {
node<k,v> p = map.replacementnode(q, null);
if (tl == null)
hd = p;
else
tl.next = p;
tl = p;
}
return hd;
}
/**
* tree version of putval.
*/
final treenode<k,v> puttreeval(hashmap<k,v> map, node<k,v>[] tab,
int h, k k, v v) {
class<?> kc = null;
boolean searched = false;
treenode<k,v> root = (parent != null) ? root() : this;
for (treenode<k,v> p = root;;) {
int dir, ph; k pk;
if ((ph = p.hash) > h)
dir = -1;
else if (ph < h)
dir = 1;
else if ((pk = p.key) == k || (k != null && k.equals(pk)))
return p;
else if ((kc == null &&
(kc = comparableclassfor(k)) == null) ||
(dir = comparecomparables(kc, k, pk)) == 0) {
if (!searched) {
treenode<k,v> q, ch;
searched = true;
if (((ch = p.left) != null &&
(q = ch.find(h, k, kc)) != null) ||
((ch = p.right) != null &&
(q = ch.find(h, k, kc)) != null))
return q;
}
dir = tiebreakorder(k, pk);
}
treenode<k,v> xp = p;
if ((p = (dir <= 0) ? p.left : p.right) == null) {
node<k,v> xpn = xp.next;
treenode<k,v> x = map.newtreenode(h, k, v, xpn);
if (dir <= 0)
xp.left = x;
else
xp.right = x;
xp.next = x;
x.parent = x.prev = xp;
if (xpn != null)
((treenode<k,v>)xpn).prev = x;
moveroottofront(tab, balanceinsertion(root, x));
return null;
}
}
}
/**
* removes the given node, that must be present before this call.
* this is messier than typical red-black deletion code because we
* cannot swap the contents of an interior node with a leaf
* successor that is pinned by "next" pointers that are accessible
* independently during traversal. so instead we swap the tree
* linkages. if the current tree appears to have too few nodes,
* the bin is converted back to a plain bin. (the test triggers
* somewhere between 2 and 6 nodes, depending on tree structure).
*/
final void removetreenode(hashmap<k,v> map, node<k,v>[] tab,
boolean movable) {
int n;
if (tab == null || (n = tab.length) == 0)
return;
int index = (n - 1) & hash;
treenode<k,v> first = (treenode<k,v>)tab[index], root = first, rl;
treenode<k,v> succ = (treenode<k,v>)next, pred = prev;
if (pred == null)
tab[index] = first = succ;
else
pred.next = succ;
if (succ != null)
succ.prev = pred;
if (first == null)
return;
if (root.parent != null)
root = root.root();
if (root == null || root.right == null ||
(rl = root.left) == null || rl.left == null) {
tab[index] = first.untreeify(map); // too small
return;
}
treenode<k,v> p = this, pl = left, pr = right, replacement;
if (pl != null && pr != null) {
treenode<k,v> s = pr, sl;
while ((sl = s.left) != null) // find successor
s = sl;
boolean c = s.red; s.red = p.red; p.red = c; // swap colors
treenode<k,v> sr = s.right;
treenode<k,v> pp = p.parent;
if (s == pr) { // p was s's direct parent
p.parent = s;
s.right = p;
}
else {
treenode<k,v> sp = s.parent;
if ((p.parent = sp) != null) {
if (s == sp.left)
sp.left = p;
else
sp.right = p;
}
if ((s.right = pr) != null)
pr.parent = s;
}
p.left = null;
if ((p.right = sr) != null)
sr.parent = p;
if ((s.left = pl) != null)
pl.parent = s;
if ((s.parent = pp) == null)
root = s;
else if (p == pp.left)
pp.left = s;
else
pp.right = s;
if (sr != null)
replacement = sr;
else
replacement = p;
}
else if (pl != null)
replacement = pl;
else if (pr != null)
replacement = pr;
else
replacement = p;
if (replacement != p) {
treenode<k,v> pp = replacement.parent = p.parent;
if (pp == null)
root = replacement;
else if (p == pp.left)
pp.left = replacement;
else
pp.right = replacement;
p.left = p.right = p.parent = null;
}
treenode<k,v> r = p.red ? root : balancedeletion(root, replacement);
if (replacement == p) { // detach
treenode<k,v> pp = p.parent;
p.parent = null;
if (pp != null) {
if (p == pp.left)
pp.left = null;
else if (p == pp.right)
pp.right = null;
}
}
if (movable)
moveroottofront(tab, r);
}
/**
* splits nodes in a tree bin into lower and upper tree bins,
* or untreeifies if now too small. called only from resize;
* see above discussion about split bits and indices.
*
* @param map the map
* @param tab the table for recording bin heads
* @param index the index of the table being split
* @param bit the bit of hash to split on
*/
final void split(hashmap<k,v> map, node<k,v>[] tab, int index, int bit) {
treenode<k,v> b = this;
// relink into lo and hi lists, preserving order
treenode<k,v> lohead = null, lotail = null;
treenode<k,v> hihead = null, hitail = null;
int lc = 0, hc = 0;
for (treenode<k,v> e = b, next; e != null; e = next) {
next = (treenode<k,v>)e.next;
e.next = null;
if ((e.hash & bit) == 0) {
if ((e.prev = lotail) == null)
lohead = e;
else
lotail.next = e;
lotail = e;
++lc;
}
else {
if ((e.prev = hitail) == null)
hihead = e;
else
hitail.next = e;
hitail = e;
++hc;
}
}
if (lohead != null) {
if (lc <= untreeify_threshold)
tab[index] = lohead.untreeify(map);
else {
tab[index] = lohead;
if (hihead != null) // (else is already treeified)
lohead.treeify(tab);
}
}
if (hihead != null) {
if (hc <= untreeify_threshold)
tab[index + bit] = hihead.untreeify(map);
else {
tab[index + bit] = hihead;
if (lohead != null)
hihead.treeify(tab);
}
}
}
/* ------------------------------------------------------------ */
// red-black tree methods, all adapted from clr
static <k,v> treenode<k,v> rotateleft(treenode<k,v> root,
treenode<k,v> p) {
treenode<k,v> r, pp, rl;
if (p != null && (r = p.right) != null) {
if ((rl = p.right = r.left) != null)
rl.parent = p;
if ((pp = r.parent = p.parent) == null)
(root = r).red = false;
else if (pp.left == p)
pp.left = r;
else
pp.right = r;
r.left = p;
p.parent = r;
}
return root;
}
static <k,v> treenode<k,v> rotateright(treenode<k,v> root,
treenode<k,v> p) {
treenode<k,v> l, pp, lr;
if (p != null && (l = p.left) != null) {
if ((lr = p.left = l.right) != null)
lr.parent = p;
if ((pp = l.parent = p.parent) == null)
(root = l).red = false;
else if (pp.right == p)
pp.right = l;
else
pp.left = l;
l.right = p;
p.parent = l;
}
return root;
}
static <k,v> treenode<k,v> balanceinsertion(treenode<k,v> root,
treenode<k,v> x) {
x.red = true;
for (treenode<k,v> xp, xpp, xppl, xppr;;) {
if ((xp = x.parent) == null) {
x.red = false;
return x;
}
else if (!xp.red || (xpp = xp.parent) == null)
return root;
if (xp == (xppl = xpp.left)) {
if ((xppr = xpp.right) != null && xppr.red) {
xppr.red = false;
xp.red = false;
xpp.red = true;
x = xpp;
}
else {
if (x == xp.right) {
root = rotateleft(root, x = xp);
xpp = (xp = x.parent) == null ? null : xp.parent;
}
if (xp != null) {
xp.red = false;
if (xpp != null) {
xpp.red = true;
root = rotateright(root, xpp);
}
}
}
}
else {
if (xppl != null && xppl.red) {
xppl.red = false;
xp.red = false;
xpp.red = true;
x = xpp;
}
else {
if (x == xp.left) {
root = rotateright(root, x = xp);
xpp = (xp = x.parent) == null ? null : xp.parent;
}
if (xp != null) {
xp.red = false;
if (xpp != null) {
xpp.red = true;
root = rotateleft(root, xpp);
}
}
}
}
}
}
static <k,v> treenode<k,v> balancedeletion(treenode<k,v> root,
treenode<k,v> x) {
for (treenode<k,v> xp, xpl, xpr;;) {
if (x == null || x == root)
return root;
else if ((xp = x.parent) == null) {
x.red = false;
return x;
}
else if (x.red) {
x.red = false;
return root;
}
else if ((xpl = xp.left) == x) {
if ((xpr = xp.right) != null && xpr.red) {
xpr.red = false;
xp.red = true;
root = rotateleft(root, xp);
xpr = (xp = x.parent) == null ? null : xp.right;
}
if (xpr == null)
x = xp;
else {
treenode<k,v> sl = xpr.left, sr = xpr.right;
if ((sr == null || !sr.red) &&
(sl == null || !sl.red)) {
xpr.red = true;
x = xp;
}
else {
if (sr == null || !sr.red) {
if (sl != null)
sl.red = false;
xpr.red = true;
root = rotateright(root, xpr);
xpr = (xp = x.parent) == null ?
null : xp.right;
}
if (xpr != null) {
xpr.red = (xp == null) ? false : xp.red;
if ((sr = xpr.right) != null)
sr.red = false;
}
if (xp != null) {
xp.red = false;
root = rotateleft(root, xp);
}
x = root;
}
}
}
else { // symmetric
if (xpl != null && xpl.red) {
xpl.red = false;
xp.red = true;
root = rotateright(root, xp);
xpl = (xp = x.parent) == null ? null : xp.left;
}
if (xpl == null)
x = xp;
else {
treenode<k,v> sl = xpl.left, sr = xpl.right;
if ((sl == null || !sl.red) &&
(sr == null || !sr.red)) {
xpl.red = true;
x = xp;
}
else {
if (sl == null || !sl.red) {
if (sr != null)
sr.red = false;
xpl.red = true;
root = rotateleft(root, xpl);
xpl = (xp = x.parent) == null ?
null : xp.left;
}
if (xpl != null) {
xpl.red = (xp == null) ? false : xp.red;
if ((sl = xpl.left) != null)
sl.red = false;
}
if (xp != null) {
xp.red = false;
root = rotateright(root, xp);
}
x = root;
}
}
}
}
}
/**
* recursive invariant check
*/
static <k,v> boolean checkinvariants(treenode<k,v> t) {
treenode<k,v> tp = t.parent, tl = t.left, tr = t.right,
tb = t.prev, tn = (treenode<k,v>)t.next;
if (tb != null && tb.next != t)
return false;
if (tn != null && tn.prev != t)
return false;
if (tp != null && t != tp.left && t != tp.right)
return false;
if (tl != null && (tl.parent != t || tl.hash > t.hash))
return false;
if (tr != null && (tr.parent != t || tr.hash < t.hash))
return false;
if (t.red && tl != null && tl.red && tr != null && tr.red)
return false;
if (tl != null && !checkinvariants(tl))
return false;
if (tr != null && !checkinvariants(tr))
return false;
return true;
}
}
}
阅后感
咱主要是写java中，理论上代码咱应该都认识，但是为什么咋一看会觉得看不懂呢？看不懂，意思是看了一遍，不知道代码想干什么。或者知道代码想干什么，但是不知道为什么那么干。
看不懂，一部分是因为一些不常见的操作太多，而且连在一起，所以产生了畏难情绪。比如一些与操作、移位运算。
一部分是因为运用了一些算法，对该算法不太了解，自然不太能看懂那段代码是想干什么。比如将链表转为红黑树。
总结：看代码要一行一行看，看一行注释一行，不明白的多搜索相关资料，不要图快。
代码感受
map在进行扩容时，直接通过计算得到元素是应该不动还是应该移动n个位置，这里确实很精妙。
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