//默认初始容量为16 static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; //默认负载因子为0.75 static final float DEFAULT_LOAD_FACTOR = 0.75f; //Hash数组(在resize()中初始化) transient Node<K,V>[] table; //元素个数 transient int size; //容量阈值(元素个数超过该值会自动扩容) int threshold;
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);//^表示相同返回0，不同返回1
//Objects.hashCode(o)————>return o != null ? o.hashCode() : 0;
}
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;
//Objects.equals(1,b)————> return (a == b) || (a != null && a.equals(b));
if (Objects.equals(key, e.getKey()) && Objects.equals(value, e.getValue()))
return true;
}
return false;
}
}
/*找到大于或等于 cap 的最小2的幂，用来做容量阈值*/
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;
}
/*传入初始容量和负载因子*/
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);
}
/*扩容*/
final Node<K,V>[] resize() {
Node<K,V>[] oldTab = table;
int oldCap = (oldTab == null) ? 0 : oldTab.length;
int oldThr = threshold;
int newCap, newThr = 0;
//1、若oldCap>0 说明hash数组table已被初始化
if (oldCap > 0) {
if (oldCap >= MAXIMUM_CAPACITY) {
threshold = Integer.MAX_VALUE;
return oldTab;
}//按当前table数组长度的2倍进行扩容，阈值也变为原来的2倍
else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY && oldCap >= DEFAULT_INITIAL_CAPACITY)
newThr = oldThr << 1;
}//2、若数组未被初始化，而threshold>0说明调用了HashMap(initialCapacity)和HashMap(initialCapacity, loadFactor)构造器
else if (oldThr > 0)
newCap = oldThr;//新容量设为数组阈值
else { //3、若table数组未被初始化，且threshold为0说明调用HashMap()构造方法
newCap = DEFAULT_INITIAL_CAPACITY;//默认为16
newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);//16*0.75
}
//若计算过程中，阈值溢出归零，则按阈值公式重新计算
if (newThr == 0) {
float ft = (float)newCap * loadFactor;
newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?
(int)ft : Integer.MAX_VALUE);
}
threshold = newThr;
//创建新的hash数组，hash数组的初始化也是在这里完成的
Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
table = newTab;
//如果旧的hash数组不为空，则遍历旧数组并映射到新的hash数组
if (oldTab != null) {
for (int j = 0; j < oldCap; j) {
Node<K,V> e;
if ((e = oldTab[j]) != null) {
oldTab[j] = null;//GC
if (e.next == null)//如果只链接一个节点，重新计算并放入新数组
newTab[e.hash & (newCap - 1)] = e;
//若是红黑树，则需要进行拆分
else if (e instanceof TreeNode)
((TreeNode<K,V>)e).split(this, newTab, j, oldCap);
else {
//rehash————>重新映射到新数组
Node<K,V> loHead = null, loTail = null;
Node<K,V> hiHead = null, hiTail = null;
Node<K,V> next;
do {
next = e.next;
/*注意这里使用的是：e.hash & oldCap，若为0则索引位置不变，不为0则新索引=原索引 旧数组长度*/
if ((e.hash & oldCap) == 0) {
if (loTail == null)
loHead = e;
else
loTail.next = e;
loTail = e;
}
else {
if (hiTail == null)
hiHead = e;
else
hiTail.next = e;
hiTail = e;
}
} while ((e = next) != null);
if (loTail != null) {
loTail.next = null;
newTab[j] = loHead;
}
if (hiTail != null) {
hiTail.next = null;
newTab[j oldCap] = hiHead;
}
}
}
}
}
return newTab;
}
static final int hash(Object key) {
int h;
return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}
public V get(Object key) {
Node<K,V> e;
return (e = getNode(hash(key), key)) == null ? null : e.value;//hash(key)不等于key.hashCode
}
final Node<K,V> getNode(int hash, Object key) {
Node<K,V>[] tab; //指向hash数组
Node<K,V> first, e; //first指向hash数组链接的第一个节点，e指向下一个节点
int n;//hash数组长度
K k;
/*(n - 1) & hash ————>根据hash值计算出在数组中的索引index（相当于对数组长度取模，这里用位运算进行了优化）*/
if ((tab = table) != null && (n = tab.length) > 0 && (first = tab[(n - 1) & hash]) != null) {
//基本类型用==比较，其它用euqals比较
if (first.hash == hash && ((k = first.key) == key || (key != null && key.equals(k))))
return first;
if ((e = first.next) != null) {
//如果first是TreeNode类型，则调用红黑树查找方法
if (first instanceof TreeNode)
return ((TreeNode<K,V>)first).getTreeNode(hash, key);
do {//向后遍历
if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k))))
return e;
} while ((e = e.next) != null);
}
}
return null;
}`
public V put(K key, V value) {
return putVal(hash(key), key, value, false, true);
}
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,boolean evict) {
Node<K,V>[] tab;//指向hash数组
Node<K,V> p;//初始化为table中第一个节点
int n, i;//n为数组长度，i为索引
//tab被延迟到插入新数据时再进行初始化
if ((tab = table) == null || (n = tab.length) == 0)
n = (tab = resize()).length;
//如果数组中不包含Node引用，则新建Node节点存入数组中即可
if ((p = tab[i = (n - 1) & hash]) == null)
tab[i] = newNode(hash, key, value, null);//new Node<>(hash, key, value, next)
else {
Node<K,V> e; //如果要插入的key-value已存在，用e指向该节点
K k;
//如果第一个节点就是要插入的key-value，则让e指向第一个节点（p在这里指向第一个节点）
if (p.hash == hash && ((k = p.key) == key || (key != null && key.equals(k))))
e = p;
//如果p是TreeNode类型，则调用红黑树的插入操作（注意：TreeNode是Node的子类）
else if (p instanceof TreeNode)
e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
else {
//对链表进行遍历，并用binCount统计链表长度
for (int binCount = 0; ; binCount) {
//如果链表中不包含要插入的key-value，则将其插入到链表尾部
if ((e = p.next) == null) {
p.next = newNode(hash, key, value, null);
//如果链表长度大于或等于树化阈值，则进行树化操作
if (binCount >= TREEIFY_THRESHOLD - 1)
treeifyBin(tab, hash);
break;
}
//如果要插入的key-value已存在则终止遍历，否则向后遍历
if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k))))
break;
p = e;
}
}
//如果e不为null说明要插入的key-value已存在
if (e != null) {
V oldValue = e.value;
//根据传入的onlyIfAbsent判断是否要更新旧值
if (!onlyIfAbsent || oldValue == null)
e.value = value;
afterNodeAccess(e);
return oldValue;
}
}
modCount;
//键值对数量超过阈值时，则进行扩容
if ( size > threshold)
resize();
afterNodeInsertion(evict);//也是空函数？回调？不知道干嘛的
return null;
}
public V remove(Object key) {
Node<K,V> e;
return (e = removeNode(hash(key), key, null, false, true)) == null ? null : e.value;
}
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;
//1、定位元素桶位置
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;
// 如果键的值与链表第一个节点相等，则将 node 指向该节点
if (p.hash == hash && ((k = p.key) == key || (key != null && key.equals(k))))
node = p;
else if ((e = p.next) != null) {
// 如果是 TreeNode 类型，调用红黑树的查找逻辑定位待删除节点
if (p instanceof TreeNode)
node = ((TreeNode<K,V>)p).getTreeNode(hash, key);
else {
// 2、遍历链表，找到待删除节点
do {
if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) {
node = e;
break;
}
p = e;
} while ((e = e.next) != null);
}
}
// 3、删除节点，并修复链表或红黑树
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;
}
Map<String, Integer> map = new HashMap<>();
map.put("1", 1);
map.put("2", 2);
map.put("3", 3);
for (String s : map.keySet()) {
if (s.equals("2"))
map.remove("2");
}
transient int modCount;
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 Iterator<K> iterator() { return new KeyIterator(); }
// 省略部分代码
}
final class KeyIterator extends HashIterator implements Iterator<K> {
public final K next() { return nextNode().key; }
}
/*HashMap迭代器基类，子类有KeyIterator、ValueIterator等*/
abstract class HashIterator {
Node<K,V> next; //下一个节点
Node<K,V> current; //当前节点
int expectedModCount; //修改次数
int index; //当前索引
//无参构造
HashIterator() {
expectedModCount = modCount;
Node<K,V>[] t = table;
current = next = null;
index = 0;
//找到第一个不为空的桶的索引
if (t != null && size > 0) {
do {} while (index < t.length && (next = t[index ]) == null);
}
}
//是否有下一个节点
public final boolean hasNext() {
return next != null;
}
//返回下一个节点
final Node<K,V> nextNode() {
Node<K,V>[] t;
Node<K,V> e = next;
if (modCount != expectedModCount)
throw new ConcurrentModificationException();//fail-fast
if (e == null)
throw new NoSuchElementException();
//当前的链表遍历完了就开始遍历下一个链表
if ((next = (current = e).next) == null && (t = table) != null) {
do {} while (index < t.length && (next = t[index ]) == null);
}
return e;
}
//删除元素
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);//调用外部的removeNode
expectedModCount = modCount;
}
}
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
`removeNode(hash(key), key, null, false, false);//调用外部的removeNode expectedModCount = modCount;`
Map<String, Integer> map = new HashMap<>();
map.put("1", 1);
map.put("2", 2);
map.put("3", 3);
Iterator<String> iterator = map.keySet().iterator();
while (iterator.hasNext()){
if (iterator.next().equals("2"))
iterator.remove();
}
public class Person {
Integer id;
String name;
public Person(Integer id, String name) {
this.id = id;
this.name = name;
}
@Override
public boolean equals(Object obj) {
if (obj == null) return false;
if (obj == this) return true;
if (obj instanceof Person) {
Person person = (Person) obj;
if (this.id == person.id)
return true;
}
return false;
}
public static void main(String[] args) {
Person p1 = new Person(1, "aaa");
Person p2 = new Person(1, "bbb");
HashMap<Person, String> map = new HashMap<>();
map.put(p1, "这是p1");
System.out.println(map.get(p2));
}
}