集合框架二4.3、HashMap线程不安全程序运行结果：java.util.ConcurrentModification

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4.3、HashMap 线程不安全

演示 HashMap 线程不安全

public class ContainerNotSafeDemo {

    public static void main(String[] args) {
        mapNotSafe();
    }

    private static void mapNotSafe() {
        Map<String,String> map=new HashMap<>();
        for (int i = 1; i <= 30; i++) {
            new Thread(() -> {
                map.put(Thread.currentThread().getName(), UUID.randomUUID().toString().substring(0, 8));
                System.out.println(Thread.currentThread().getName() + "\t" + map);
            }, String.valueOf(i)).start();
        }
    }
}
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程序运行结果：java.util.ConcurrentModificationException

java.util.ConcurrentModificationException at java.util.HashMap $HashIterator.nextNode(HashMap.java:1437) at java.util.HashMap$ EntryIterator.next(HashMap.java:1471) at java.util.HashMap $EntryIterator.next(HashMap.java:1469) at java.util.AbstractMap.toString(AbstractMap.java:554) at java.lang.String.valueOf(String.java:2994) at java.lang.StringBuilder.append(StringBuilder.java:131) at com.Heygo.ContainerNotSafeDemo.lambda$ mapNotSafe$1(ContainerNotSafeDemo.java:60) at java.lang.Thread.run(Thread.java:748) 123456789

解决 HashMap 线程不安全

代码：使用 ConcurrentHashMap 类

public class ContainerNotSafeDemo { public static void main(String[] args) { mapNotSafe(); }

private static void mapNotSafe() {
    Map<String,String> map=new ConcurrentHashMap<>();
    for (int i = 1; i <= 30; i++) {
        new Thread(() -> {
            map.put(Thread.currentThread().getName(), UUID.randomUUID().toString().substring(0, 8));
            System.out.println(Thread.currentThread().getName() + "\t" + map);
        }, String.valueOf(i)).start();
    }
}

} 12345678910111213141516171819202122

程序运行结果

12 {11=ae36bafc, 12=16de3027, 13=dcb688cc, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 10=8f6933de} 16 {11=ae36bafc, 12=16de3027, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 16=0c7d1777, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 10=8f6933de} 4 {11=ae36bafc, 12=16de3027, 1=bf7bc1a8, 13=dcb688cc, 2=d479c1fe, 14=ba2e61d8, 3=f036e44c, 15=f9c89bc1, 4=71eba0d9, 16=0c7d1777, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 10=8f6933de} 19 {11=ae36bafc, 12=16de3027, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 16=0c7d1777, 19=801d369c, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 10=8f6933de} 6 {11=ae36bafc, 12=16de3027, 1=bf7bc1a8, 13=dcb688cc, 2=d479c1fe, 14=ba2e61d8, 3=f036e44c, 15=f9c89bc1, 4=71eba0d9, 16=0c7d1777, 5=8d4fab3b, 17=7f64e3ee, 6=ad508f93, 7=cb593b6f, 19=801d369c, 8=8c1542fa, 9=31d873ac, 10=8f6933de} 7 {11=ae36bafc, 12=16de3027, 1=bf7bc1a8, 13=dcb688cc, 2=d479c1fe, 14=ba2e61d8, 3=f036e44c, 15=f9c89bc1, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 10=8f6933de} 1 {11=ae36bafc, 12=16de3027, 1=bf7bc1a8, 13=dcb688cc, 2=d479c1fe, 14=ba2e61d8, 3=f036e44c, 15=f9c89bc1, 4=71eba0d9, 16=0c7d1777, 5=8d4fab3b, 17=7f64e3ee, 6=ad508f93, 18=3c3c1d41, 7=cb593b6f, 19=801d369c, 8=8c1542fa, 9=31d873ac, 20=6926e455, 10=8f6933de, 21=f8e65c72} 22 {11=ae36bafc, 22=3af2e92c, 12=16de3027, 23=e96165a6, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 16=0c7d1777, 17=7f64e3ee, 18=3c3c1d41, 19=801d369c, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 20=6926e455, 10=8f6933de, 21=f8e65c72} 25 {22=3af2e92c, 23=e96165a6, 25=71972304, 10=8f6933de, 11=ae36bafc, 12=16de3027, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 16=0c7d1777, 17=7f64e3ee, 18=3c3c1d41, 19=801d369c, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 20=6926e455, 21=f8e65c72} 2 {11=ae36bafc, 12=16de3027, 1=bf7bc1a8, 13=dcb688cc, 2=d479c1fe, 14=ba2e61d8, 3=f036e44c, 15=f9c89bc1, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 10=8f6933de} 28 {22=3af2e92c, 23=e96165a6, 24=961abac9, 25=71972304, 26=a58c6246, 27=0b742cd8, 28=efe599df, 10=8f6933de, 11=ae36bafc, 12=16de3027, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 16=0c7d1777, 17=7f64e3ee, 18=3c3c1d41, 19=801d369c, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 20=6926e455, 21=f8e65c72} 3 {11=ae36bafc, 12=16de3027, 1=bf7bc1a8, 13=dcb688cc, 2=d479c1fe, 14=ba2e61d8, 3=f036e44c, 15=f9c89bc1, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 10=8f6933de} 15 {11=ae36bafc, 12=16de3027, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 10=8f6933de} 14 {11=ae36bafc, 12=16de3027, 13=dcb688cc, 14=ba2e61d8, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 10=8f6933de} 30 {22=3af2e92c, 23=e96165a6, 24=961abac9, 25=71972304, 26=a58c6246, 27=0b742cd8, 28=efe599df, 29=ecd71129, 30=7c2cc2a8, 10=8f6933de, 11=ae36bafc, 12=16de3027, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 16=0c7d1777, 17=7f64e3ee, 18=3c3c1d41, 19=801d369c, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 20=6926e455, 21=f8e65c72} 29 {22=3af2e92c, 23=e96165a6, 24=961abac9, 25=71972304, 26=a58c6246, 27=0b742cd8, 28=efe599df, 29=ecd71129, 10=8f6933de, 11=ae36bafc, 12=16de3027, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 16=0c7d1777, 17=7f64e3ee, 18=3c3c1d41, 19=801d369c, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 20=6926e455, 21=f8e65c72} 24 {22=3af2e92c, 23=e96165a6, 24=961abac9, 25=71972304, 26=a58c6246, 27=0b742cd8, 10=8f6933de, 11=ae36bafc, 12=16de3027, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 16=0c7d1777, 17=7f64e3ee, 18=3c3c1d41, 19=801d369c, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 20=6926e455, 21=f8e65c72} 26 {22=3af2e92c, 23=e96165a6, 25=71972304, 26=a58c6246, 10=8f6933de, 11=ae36bafc, 12=16de3027, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 16=0c7d1777, 17=7f64e3ee, 18=3c3c1d41, 19=801d369c, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 20=6926e455, 21=f8e65c72} 27 {22=3af2e92c, 23=e96165a6, 24=961abac9, 25=71972304, 26=a58c6246, 27=0b742cd8, 10=8f6933de, 11=ae36bafc, 12=16de3027, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 16=0c7d1777, 17=7f64e3ee, 18=3c3c1d41, 19=801d369c, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 20=6926e455, 21=f8e65c72} 23 {11=ae36bafc, 12=16de3027, 23=e96165a6, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 16=0c7d1777, 17=7f64e3ee, 18=3c3c1d41, 19=801d369c, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 20=6926e455, 10=8f6933de, 21=f8e65c72} 5 {11=ae36bafc, 12=16de3027, 1=bf7bc1a8, 13=dcb688cc, 2=d479c1fe, 14=ba2e61d8, 3=f036e44c, 15=f9c89bc1, 4=71eba0d9, 16=0c7d1777, 5=8d4fab3b, 17=7f64e3ee, 6=ad508f93, 18=3c3c1d41, 7=cb593b6f, 19=801d369c, 8=8c1542fa, 9=31d873ac, 20=6926e455, 10=8f6933de, 21=f8e65c72} 13 {11=ae36bafc, 12=16de3027, 1=bf7bc1a8, 13=dcb688cc, 2=d479c1fe, 14=ba2e61d8, 3=f036e44c, 15=f9c89bc1, 4=71eba0d9, 16=0c7d1777, 5=8d4fab3b, 17=7f64e3ee, 6=ad508f93, 18=3c3c1d41, 7=cb593b6f, 19=801d369c, 8=8c1542fa, 9=31d873ac, 20=6926e455, 10=8f6933de, 21=f8e65c72} 21 {11=ae36bafc, 12=16de3027, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 16=0c7d1777, 17=7f64e3ee, 18=3c3c1d41, 19=801d369c, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 20=6926e455, 10=8f6933de, 21=f8e65c72} 20 {11=ae36bafc, 12=16de3027, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 16=0c7d1777, 17=7f64e3ee, 18=3c3c1d41, 19=801d369c, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 20=6926e455, 10=8f6933de} 10 {11=ae36bafc, 12=16de3027, 1=bf7bc1a8, 13=dcb688cc, 2=d479c1fe, 14=ba2e61d8, 3=f036e44c, 15=f9c89bc1, 4=71eba0d9, 16=0c7d1777, 5=8d4fab3b, 17=7f64e3ee, 6=ad508f93, 18=3c3c1d41, 7=cb593b6f, 19=801d369c, 8=8c1542fa, 9=31d873ac, 20=6926e455, 10=8f6933de} 18 {11=ae36bafc, 12=16de3027, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 16=0c7d1777, 17=7f64e3ee, 18=3c3c1d41, 19=801d369c, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 20=6926e455, 10=8f6933de} 9 {11=ae36bafc, 12=16de3027, 1=bf7bc1a8, 13=dcb688cc, 2=d479c1fe, 14=ba2e61d8, 3=f036e44c, 15=f9c89bc1, 4=71eba0d9, 16=0c7d1777, 5=8d4fab3b, 17=7f64e3ee, 6=ad508f93, 18=3c3c1d41, 7=cb593b6f, 19=801d369c, 8=8c1542fa, 9=31d873ac, 10=8f6933de} 17 {11=ae36bafc, 12=16de3027, 13=dcb688cc, 14=ba2e61d8, 15=f9c89bc1, 16=0c7d1777, 17=7f64e3ee, 19=801d369c, 1=bf7bc1a8, 2=d479c1fe, 3=f036e44c, 4=71eba0d9, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 10=8f6933de} 8 {11=ae36bafc, 12=16de3027, 1=bf7bc1a8, 13=dcb688cc, 2=d479c1fe, 14=ba2e61d8, 3=f036e44c, 15=f9c89bc1, 4=71eba0d9, 16=0c7d1777, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 19=801d369c, 8=8c1542fa, 9=31d873ac, 10=8f6933de} 11 {11=ae36bafc, 12=16de3027, 1=bf7bc1a8, 13=dcb688cc, 2=d479c1fe, 14=ba2e61d8, 3=f036e44c, 15=f9c89bc1, 4=71eba0d9, 16=0c7d1777, 5=8d4fab3b, 6=ad508f93, 7=cb593b6f, 8=8c1542fa, 9=31d873ac, 10=8f6933de} 123456789101112131415161718192021222324252627282930

HashMap 底层源码

参考资料：www.cnblogs.com/iwenwen/p/1…
HashMap 中维护了一个 KV 链表数组：Node<K,V>[]

transient Node<K,V>[] table; 1

构造方法

默认构造函数：负载因子为 0.75

static final float DEFAULT_LOAD_FACTOR = 0.75f;

/**
 * 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
}

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通过另一个 Map 创建 HashMap

// 包含另一个“Map”的构造函数 public HashMap(Map<? extends K, ? extends V> m) { this.loadFactor = DEFAULT_LOAD_FACTOR; putMapEntries(m, false);//下面会分析到这个方法 }

final void putMapEntries(Map<? extends K, ? extends V> m, boolean evict) { int s = m.size(); if (s > 0) { // 判断table是否已经初始化 if (table == null) { // pre-size // 未初始化，s为m的实际元素个数 float ft = ((float)s / loadFactor) + 1.0F; int t = ((ft < (float)MAXIMUM_CAPACITY) ? (int)ft : MAXIMUM_CAPACITY); // 计算得到的t大于阈值，则初始化阈值 if (t > threshold) threshold = tableSizeFor(t); } // 已初始化，并且m元素个数大于阈值，进行扩容处理 else if (s > threshold) resize(); // 将m中的所有元素添加至HashMap中 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); } } } 123456789101112131415161718192021222324252627282930
指定初始容量大小的构造函数

// 指定“容量大小”的构造函数 public HashMap(int initialCapacity) { this(initialCapacity, DEFAULT_LOAD_FACTOR); } 1234
指定初始容量大小和负载因子的构造函数

// 指定“容量大小”和“加载因子”的构造函数 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); } 1234567891011

添加元素

put() 方法添加元素：
- 如果 tab 数组为空或者长度为 0 ，则扩容
- 如果定位到的数组位置没有元素就直接插入
- 如果定位到的数组位置有元素就和要插入的key比较
  - 如果key相同就直接覆盖
  - 如果key不相同，就判断p是否是一个树节点
    - 如果是就调用 e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value); 将元素添加进 HashMap 中
    - 如果不是就遍历链表插入(插入在链表尾部)
public V put(K key, V value) { return putVal(hash(key), key, value, false, true); }

static final int hash(Object key) { int h; return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16); }

final V putVal(int hash, K key, V value, boolean onlyIfAbsent, boolean evict) { Node<K,V>[] tab; Node<K,V> p; int n, i; // table未初始化或者长度为0，进行扩容 if ((tab = table) == null || (n = tab.length) == 0) n = (tab = resize()).length; // (n - 1) & hash 确定元素存放在哪个桶中，桶为空，新生成结点放入桶中(此时，这个结点是放在数组中) if ((p = tab[i = (n - 1) & hash]) == null) tab[i] = newNode(hash, key, value, null); // 桶中已经存在元素 else { Node<K,V> e; K k; // 比较桶中第一个元素(数组中的结点)的hash值相等，key相等 if (p.hash == hash && ((k = p.key) == key || (key != null && key.equals(k)))) // 将第一个元素赋值给e，用e来记录 e = p; // hash值不相等，即key不相等；为红黑树结点 else if (p instanceof TreeNode) // 放入树中 e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value); // 为链表结点 else { // 在链表最末插入结点 for (int binCount = 0; ; ++binCount) { // 到达链表的尾部 if ((e = p.next) == null) { // 在尾部插入新结点 p.next = newNode(hash, key, value, null); // 结点数量达到阈值，转化为红黑树 if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st treeifyBin(tab, hash); // 跳出循环 break; } // 判断链表中结点的key值与插入的元素的key值是否相等 if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) // 相等，跳出循环 break; // 用于遍历桶中的链表，与前面的e = p.next组合，可以遍历链表 p = e; } } // 表示在桶中找到key值、hash值与插入元素相等的结点 if (e != null) { // 记录e的value V oldValue = e.value; // onlyIfAbsent为false或者旧值为null if (!onlyIfAbsent || oldValue == null) //用新值替换旧值 e.value = value; // 访问后回调 afterNodeAccess(e); // 返回旧值 return oldValue; } } // 结构性修改 ++modCount; // 实际大小大于阈值则扩容 if (++size > threshold) resize(); // 插入后回调 afterNodeInsertion(evict); return null; } 12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576
put 方法流程图

get 方法：如果数组对应位置为 null ，则直接返回 null ，否则去对应链表或者红黑树中去取

public V get(Object key) { Node<K,V> e; return (e = getNode(hash(key), key)) == null ? null : e.value; }

final Node<K,V> getNode(int hash, Object key) { Node<K,V>[] tab; Node<K,V> first, e; int n; K k; if ((tab = table) != null && (n = tab.length) > 0 && (first = tab[(n - 1) & hash]) != null) { // 数组元素相等 if (first.hash == hash && // always check first node ((k = first.key) == key || (key != null && key.equals(k)))) return first; // 桶中不止一个节点 if ((e = first.next) != null) { // 在树中get if (first instanceof TreeNode) return ((TreeNode<K,V>)first).getTreeNode(hash, key); // 在链表中get do { if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) return e; } while ((e = e.next) != null); } } return null; } 12345678910111213141516171819202122232425262728
resize方法：进行扩容，会伴随着一次重新hash分配，并且会遍历hash表中所有的元素，是非常耗时的。在编写程序中，要尽量避免resize

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) { // 超过最大值就不再扩充了，就只好随你碰撞去吧 if (oldCap >= MAXIMUM_CAPACITY) { threshold = Integer.MAX_VALUE; return oldTab; } // 没超过最大值，就扩充为原来的2倍 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 { // signifies using defaults newCap = DEFAULT_INITIAL_CAPACITY; newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY); } // 计算新的resize上限 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; if (oldTab != null) { // 把每个bucket都移动到新的buckets中 for (int j = 0; j < oldCap; ++j) { Node<K,V> e; if ((e = oldTab[j]) != null) { oldTab[j] = null; 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 { Node<K,V> loHead = null, loTail = null; Node<K,V> hiHead = null, hiTail = null; Node<K,V> next; do { next = e.next; // 原索引 if ((e.hash & oldCap) == 0) { if (loTail == null) loHead = e; else loTail.next = e; loTail = e; } // 原索引+oldCap else { if (hiTail == null) hiHead = e; else hiTail.next = e; hiTail = e; } } while ((e = next) != null); // 原索引放到bucket里 if (loTail != null) { loTail.next = null; newTab[j] = loHead; } // 原索引+oldCap放到bucket里 if (hiTail != null) { hiTail.next = null; newTab[j + oldCap] = hiHead; } } } } } return newTab; }