模拟hashmap,运行扩容流程

真实代码

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;        @SuppressWarnings({"rawtypes","unchecked"})            Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];        table = newTab;        if (oldTab != null) {            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 { // preserve order                    //以e.hash & oldCap是否为0进行数据分割，将一个桶的数据分散到两个桶里。                        Node<K,V> loHead = null, loTail = null;                        Node<K,V> hiHead = null, hiTail = null;                        Node<K,V> next;                        do {                            next = e.next;                            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) {                       //最后一个节点的next置空，防止死循环                            loTail.next = null;                        //此部分存储数据位置不变                            newTab[j] = loHead;                        }                        if (hiTail != null) {                        //最后一个节点的next置空，防止死循环                            hiTail.next = null;                            //此部分存储数据是从原来的桶切分出来的                            //在新table中的位置为原位置+T[原表长度]                            newTab[j + oldCap] = hiHead;                        }                    }                }            }        }        return newTab;    }

模拟代码

package action;import java.util.Map;import java.util.Objects;public class TestClass<K,V>{    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;        }    }    public static void main(String[] args) {        Node<String, String> loHead0 = new Node<String, String>(3303, "10", "10", null);        Node<String, String> loHead1 = new Node<String, String>(3303, "20", "20", loHead0);        Node<String, String> loHead2 = new Node<String, String>(3303, "30", "30", loHead1);        Node<String, String> loHead3 = new Node<String, String>(3303, "40", "40", loHead2);        Node<String, String> loHead4 = new Node<String, String>(3303, "50", "50", loHead3);        Node<String, String> loHead5 = new Node<String, String>(3303, "60", "60", loHead4);        Node<String, String>[] oldTab = (Node<String, String>[])new Node[16];        oldTab[5] = loHead5;        Node<String, String>[] newTab = (Node<String, String>[])new Node[32];        for (int j = 0; j < oldTab.length ; ++j) {            Node<String, String> e;            if ((e = oldTab[j]) != null) {                    Node<String, String> next;                    Node<String, String> loHead = null, loTail = null;                    Node<String, String> hiHead = null, hiTail = null;                    boolean flag = true;                    do {                        next = loHead5.next;                        if (flag) {                            if (loTail == null)                                loHead = loHead5;                            else                                loTail.next = loHead5;                            loTail = loHead5;                            flag = false;                        }                        else {                            if (hiTail == null)                                hiHead = loHead5;                            else                                hiTail.next = loHead5;                            hiTail = loHead5;                            flag = true;                        }                    } while ((loHead5 = next) != null);                    if (loTail != null) {                        loTail.next = null;                        newTab[j] = loHead;                    }                    if (hiTail != null) {                        hiTail.next = null;                        newTab[j + oldTab.length] = hiHead;                    }                }            }        }    }

扩容前:

扩容后: