作者:我是雅小贱- | 来源:互联网 | 2023-08-13 21:34
前提知识:常见数据结构(暂未发布)java.lang.Object的hashcode与equals函数HashMap的数据结构--基于hash表实现源码分析:补充:(
前提知识:
常见数据结构
(暂未发布)java.lang.Object的hashcode与equals函数
HashMap的数据结构--基于hash表实现
源码分析: 补充:(暂未发布)transient瞬态非序列化关键字详情
public class HashMap{
//链表的数组容器
transient Node[] table;
transient int size;//存放元素的个数
int threshold; //临界值 当实际大小超过临界值时,会进行扩容threshold = 加载因子*容量
final float loadFactor; //加载因子
transient int modCount;//被修改的次数
//结论:Map里面的内容都保存在Node[]里面
static class Node implements Map.Entry {
final int hash;
final K key; //可以看出map的key键的变量容器
V value; //可以看出map的key键对应value值的变量容器
Node next; //用与链表的下一个值得hashcode地址
public final int hashCode() {
return Objects.hashCode(key) ^ Objects.hashCode(value);
}
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;
}
}
}
存值put实现:
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[] tab; Node p; int n, i;
if ((tab = table) == null || (n = tab.length) == 0)
n = (tab = resize()).length;
if ((p = tab[i = (n - 1) & hash]) == null)
tab[i] = newNode(hash, key, value, null);
else {
Node e; K k;
if (p.hash == hash &&((k = p.key) == key || (key != null && key.equals(k))))
e = p;
else if (p instanceof TreeNode)
e = ((TreeNode)p).putTreeVal(this, tab, hash, key, value);
else {
for (int binCount = 0; ; ++binCount) {
if ((e = p.next) == null) {
p.next = newNode(hash, key, value, null);
if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
treeifyBin(tab, hash);
break;
}
if (e.hash == hash &&((k = e.key) == key || (key != null && key.equals(k))))
break;
p = e;
}
}
if (e != null) { // existing mapping for key
V oldValue = e.value;
if (!onlyIfAbsent || oldValue == null)
e.value = value;
afterNodeAccess(e);
return oldValue;
}
}
++modCount;
if (++size > threshold)
resize();
afterNodeInsertion(evict);
return null;
}
ConcurrentHashMap源码片段分析:
通过利用存值put时利用synchronize同步代码块解决多线程存值的线程安全问题
public V put(K key, V value) {
return putVal(key, value, false);
}
/** Implementation for put and putIfAbsent */
final V putVal(K key, V value, boolean onlyIfAbsent) {
if (key == null || value == null) throw new NullPointerException();
int hash = spread(key.hashCode());
int binCount = 0;
for (Node[] tab = table;;) {
Node f; int n, i, fh;
if (tab == null || (n = tab.length) == 0)
tab = initTable();
else if ((f = tabAt(tab, i = (n - 1) & hash)) == null) {
if (casTabAt(tab, i, null,
new Node(hash, key, value, null)))
break; // no lock when adding to empty bin
}
else if ((fh = f.hash) == MOVED)
tab = helpTransfer(tab, f);
else {
V oldVal = null;
synchronized (f) { //ConcurrentHashMap线程安全的本质是通过利用存值put时利用synchronize同步代码块解决多线程存值的线程安全问题 if (tabAt(tab, i) == f) {
if (fh >= 0) {
binCount = 1;
for (Node e = f;; ++binCount) {
K ek;
if (e.hash == hash &&
((ek = e.key) == key ||
(ek != null && key.equals(ek)))) {
oldVal = e.val;
if (!onlyIfAbsent)
e.val = value;
break;
}
Node pred = e;
if ((e = e.next) == null) {
pred.next = new Node(hash, key,
value, null);
break;
}
}
}
else if (f instanceof TreeBin) {
Node p;
binCount = 2;
if ((p = ((TreeBin)f).putTreeVal(hash, key,
value)) != null) {
oldVal = p.val;
if (!onlyIfAbsent)
p.val = value;
}
}
}
}
if (binCount != 0) {
if (binCount >= TREEIFY_THRESHOLD)
treeifyBin(tab, i);
if (oldVal != null)
return oldVal;
break;
}
}
}
addCount(1L, binCount);
return null;
}