TreeMap

一.层次图

TreeMap 是一个有序的key-value集合，它是通过[红黑树实现的。
TreeMap 继承于AbstractMap，所以它是一个Map，即一个key-value集合。
TreeMap 实现了NavigableMap接口，意味着它支持一系列的导航方法。比如返回有序的key集合

二.结构

详解：http://blog.csdn.net/chenssy/article/details/26668941
*存储结构：红黑树

  static final class Entry implements Map.Entry {
        K key;
        V value;
        Entry left = null;
        Entry right = null;
        Entry parent;
        boolean color = BLACK;
    }

• put方法

public V put(K key, V value) {
        Entry t = root;
        //创建根节点
        if (t == null) {
            compare(key, key); //确保key不为空
            root = new Entry<>(key, value, null);
             ....
        }
        int cmp;
        Entry parent;
        // split comparator and comparable paths
        Comparator cpr = comparator;
        //有自定comparator使用自定，否则使用默认的自然排序
        if (cpr != null) {
            do {
                parent = t;
                cmp = cpr.compare(key, t.key);
                if (cmp < 0)
                    t = t.left;
                else if (cmp > 0)
                    t = t.right;
                else
                    return t.setValue(value);//相等则更新值
            } while (t != null);
        } else {
         .......
            } while (t != null);
        }
    //创建要插入的父节点的子节点，小左大右，
        Entry e = new Entry<>(key, value, parent);
        if (cmp < 0)
            parent.left = e;
        else
            parent.right = e;
  //将普通二叉树转化为红黑树
        fixAfterInsertion(e);
        size++;
        return null;
    }

• 普通二叉树转化为红黑树

 private void fixAfterInsertion(Entry x) {
        x.color = RED;

        while (x != null && x != root && x.parent.color == RED) {
            if (parentOf(x) == leftOf(parentOf(parentOf(x)))) {
                Entry y = rightOf(parentOf(parentOf(x)));
                if (colorOf(y) == RED) {
                    setColor(parentOf(x), BLACK);
                    setColor(y, BLACK);
                    setColor(parentOf(parentOf(x)), RED);
                    x = parentOf(parentOf(x));
                } else {
                    if (x == rightOf(parentOf(x))) {
                        x = parentOf(x);
                        rotateLeft(x);
                    }
                    setColor(parentOf(x), BLACK);
                    setColor(parentOf(parentOf(x)), RED);
                    rotateRight(parentOf(parentOf(x)));
                }
            } else {
                Entry y = leftOf(parentOf(parentOf(x)));
                if (colorOf(y) == RED) {
                    setColor(parentOf(x), BLACK);
                    setColor(y, BLACK);
                    setColor(parentOf(parentOf(x)), RED);
                    x = parentOf(parentOf(x));
                } else {
                    if (x == leftOf(parentOf(x))) {
                        x = parentOf(x);
                        rotateRight(x);
                    }
                    setColor(parentOf(x), BLACK);
                    setColor(parentOf(parentOf(x)), RED);
                    rotateLeft(parentOf(parentOf(x)));
                }
            }
        }
        root.color = BLACK;
    }
  //左旋
  private void rotateLeft(Entry p) {
        if (p != null) {
            Entry r = p.right;
            p.right = r.left;
            if (r.left != null)
                r.left.parent = p;
            r.parent = p.parent;
            if (p.parent == null)
                root = r;
            else if (p.parent.left == p)
                p.parent.left = r;
            else
                p.parent.right = r;
            r.left = p;
            p.parent = r;
        }
    }

    //右旋
    private void rotateRight(Entry p) {
        if (p != null) {
            Entry l = p.left;
            p.left = l.right;
            if (l.right != null) l.right.parent = p;
            l.parent = p.parent;
            if (p.parent == null)
                root = l;
            else if (p.parent.right == p)
                p.parent.right = l;
            else p.parent.left = l;
            l.right = p;
            p.parent = l;
        }
    }
   //上色
  private static  void setColor(Entry p, boolean c) {
        if (p != null)
            p.color = c;
    }

• 删除操作（略类似）
  private void deleteEntry(Entry p) { ... }
  private void fixAfterDeletion(Entry x) { ... }