面试官问JDK7和JDK8的HashMap不一样在哪里？我懵了

static final int DEFAULT_INITIAL_CAPACITY = 16;
static final float DEFAULT_LOAD_FACTOR = 0.75F;
int threshold;
final float loadFactor;


static class Entry<K, V> implements java.util.Map.Entry<K, V> {
    final K key;
    V value;
    HashMap.Entry<K, V> next;
    int hash;

    Entry(int var1, K var2, V var3, HashMap.Entry<K, V> var4) {
        this.value = var3;
        this.next = var4;
        this.key = var2;
        this.hash = var1;
    }
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.

 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);
 }
 
    public HashMap(int initialCapacity) {
            this(initialCapacity, DEFAULT_LOAD_FACTOR);
    }
        
    public HashMap() {
         this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted
    }
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.

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;
        threshold = initialCapacity;
        init();
    }
 
    public HashMap(int initialCapacity) {
        this(initialCapacity, DEFAULT_LOAD_FACTOR);
    }
 
    public HashMap() {
        this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);
    }
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.

/**
   * 红黑树的插入操作
   */
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;;) {
    //dir:遍历的方向， ph:p节点的hash值
                int dir, ph; K pk;
    //红黑树是根据hash值来判断大小
    // -1:左孩子方向 1:右孩子方向
                if ((ph = p.hash) > h)
                    dir = -1;
                else if (ph < h)
                    dir = 1;
    //如果key存在的话就直接返回当前节点
                else if ((pk = p.key) == k || (k != null && k.equals(pk)))
                    return p;
    //如果当前插入的类型和正在比较的节点的Key是Comparable的话，就直接通过此接口比较
                else if ((kc == null &&
                          (kc = comparableClassFor(k)) == null) ||
                         (dir = compareComparables(kc, k, pk)) == 0) {
                    if (!searched) {
                        TreeNode<K,V> q, ch;
                        searched = true;
      //尝试在p的左子树或者右子树中找到了目标元素
                        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;
                    }
     //获取遍历的方向
                    dir = tieBreakOrder(k, pk);
                }
    //上面的所有if-else判断都是在判断下一次进行遍历的方向，即dir
                TreeNode<K,V> xp = p;
    //当下面的if判断进去之后就代表找到了目标操作元素,即xp
                if ((p = (dir <= 0) ? p.left : p.right) == null) {
                    Node<K,V> xpn = xp.next;
     //插入新的元素
                    TreeNode<K,V> x = map.newTreeNode(h, k, v, xpn);
                    if (dir <= 0)
                        xp.left = x;
                    else
                        xp.right = x;
     //因为TreeNode今后可能退化成链表，在这里需要维护链表的next属性
                    xp.next = x;
     //完成节点插入操作
                    x.parent = x.prev = xp;
                    if (xpn != null)
                        ((TreeNode<K,V>)xpn).prev = x;
     //插入操作完成之后就要进行一定的调整操作了
                    moveRootToFront(tab, balanceInsertion(root, x));
                    return null;
                }
       }
}
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.