TreeMap小抄

 public class TreeMap {
    // 红黑树实现
    // 树的层数不会差的太远，使得所有操作的复杂度不超过 O（lgn）
    // 但也使得插入，修改时要复杂的左旋右旋来保持树的平衡。
    static final class Entry implements Map.Entry {
        K key;
        V value;
        Entry left;
        Entry right;
        Entry parent;
        boolean color = BLACK;
        ...
    }
    
    // 修改值会做比较，代价比HashMap要大
    public V put(K key, V value) {
        Entry t = root;
        if (t == null) {
            compare(key, key); // type (and possibly null) check

            root = new Entry<>(key, value, null);
            size = 1;
            modCount++;
            return null;
        }
        int cmp;
        Entry parent;
        // split comparator and comparable paths
        // 插入值都会根据比较器结果放到树的左边或右边
        Comparator cpr = comparator;
        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);
            } while (t != null);
        }
        else {
            if (key == null)
                throw new NullPointerException();
            @SuppressWarnings("unchecked")
                // 没有指定比较器，按key得comparable接口比较
                Comparable k = (Comparable) key;
            do {
                parent = t;
                cmp = k.compareTo(t.key);
                if (cmp < 0)
                    t = t.left;
                else if (cmp > 0)
                    t = t.right;
                else
                    return t.setValue(value);
            } while (t != null);
        }
        Entry e = new Entry<>(key, value, parent);
        if (cmp < 0)
            parent.left = e;
        else
            parent.right = e;
        fixAfterInsertion(e);
        size++;
        modCount++;
        return null;
    }
    
    public K firstKey() {
        return key(getFirstEntry());
    }
    
    // 第一个节点即最左边的节点
    final Entry getFirstEntry() {
        Entry p = root;
        if (p != null)
            while (p.left != null)
                p = p.left;
        return p;
    }
    
    // 最后一个节点即最右边的节点
    final Entry getLastEntry() {
        Entry p = root;
        if (p != null)
            while (p.right != null)
                p = p.right;
        return p;
    }
 }