一 特性

• 有序，不允许重复,基于红黑树实现有序性，这里的有序是通过Compare进行比较的有序，并非是添加顺序
• TreeMap基于红黑树实现，根据键的自然顺序进行排序，或者使用Comparator进行排序。
• 非同步的，迭代器iterator方法返回的是fail-fastl

  二 属性

  ```java //比较器 private final Comparator<? super K> comparator; //根节点 private transient Entry root; //大小 private transient int size = 0;

//操作次数 private transient int modCount = 0;

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# 三 重要方法
- fixAfterInsertion 
   - 红黑树插入之后的旋转过程
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# 四 构造方法
```java
    public TreeMap() {
        comparator = null;
    }
    public TreeMap(Comparator<? super K> comparator) {
        this.comparator = comparator;
    }
//从map初始化
    public TreeMap(Map<? extends K, ? extends V> m) {
        comparator = null;
        putAll(m);
    }
    public TreeMap(SortedMap<K, ? extends V> m) {
        comparator = m.comparator();
        try {
            buildFromSorted(m.size(), m.entrySet().iterator(), null, null);
        } catch (java.io.IOException cannotHappen) {
        } catch (ClassNotFoundException cannotHappen) {
        }
    }

五 添加元素

    public V put(K key, V value) {
        Entry<K,V> t = root;
        //根节点为空的情况初始化
        if (t == null) {
            compare(key, key); // type (and possibly null) check
            root = new Entry<>(key, value, null);
            size = 1;
            modCount++;
            return null;
        }
        int cmp;
        //下边为红黑树的插入
        Entry<K,V> parent;
        // split comparator and comparable paths
        Comparator<? super K> cpr = comparator;
        if (cpr != null) {
            //正常的二叉树插入流程
            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")
                Comparable<? super K> k = (Comparable<? super K>) key;
            //无比较器的插入
            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<K,V> e = new Entry<>(key, value, parent);
        if (cmp < 0)
            parent.left = e;
        else
            parent.right = e;
        //这个是红黑树插入之后的旋转流程  
        fixAfterInsertion(e);
        size++;
        modCount++;
        return null;
    }

六 删除元素

    public V remove(Object key) {
        Entry<K,V> p = getEntry(key);
        if (p == null)
            return null;
        V oldValue = p.value;
        deleteEntry(p);
        return oldValue;
    }
private void deleteEntry(Entry<K,V> p) {
        modCount++;
        size--;
        // If strictly internal, copy successor's element to p and then make p
        // point to successor.
        if (p.left != null && p.right != null) {
            //找到替代的节点
            Entry<K,V> s = successor(p);
            p.key = s.key;
            p.value = s.value;
            p = s;
        } // p has 2 children
        // Start fixup at replacement node, if it exists.
        Entry<K,V> replacement = (p.left != null ? p.left : p.right);
        if (replacement != null) {
            // Link replacement to parent
            replacement.parent = p.parent;
            if (p.parent == null)
                root = replacement;
            else if (p == p.parent.left)
                p.parent.left  = replacement;
            else
                p.parent.right = replacement;
            // Null out links so they are OK to use by fixAfterDeletion.
            p.left = p.right = p.parent = null;
            // Fix replacement
            if (p.color == BLACK)
                //修复红黑树
                fixAfterDeletion(replacement);
        } else if (p.parent == null) { // return if we are the only node.
            root = null;
        } else { //  No children. Use self as phantom replacement and unlink.
            if (p.color == BLACK)
                fixAfterDeletion(p);
            if (p.parent != null) {
                if (p == p.parent.left)
                    p.parent.left = null;
                else if (p == p.parent.right)
                    p.parent.right = null;
                p.parent = null;
            }
        }
    }

七 获取元素

    final Entry<K,V> getEntry(Object key) {
        // Offload comparator-based version for sake of performance
        //如果指定了比较器则使用指定比较器进行查找
        if (comparator != null)
            return getEntryUsingComparator(key);
        if (key == null)
            throw new NullPointerException();
        @SuppressWarnings("unchecked")
            Comparable<? super K> k = (Comparable<? super K>) key;
        Entry<K,V> p = root;
        //遍历红黑树查找  使用comparetor
        while (p != null) {
            int cmp = k.compareTo(p.key);
            if (cmp < 0)
                p = p.left;
            else if (cmp > 0)
                p = p.right;
            else
                return p;
        }
        return null;
    }