还是从几个常用的方法如数:

1. public TreeMap() {...}
2. public V put(K key, V value) {...}
3. public V get(Object key) {...}

TreeMap.TreeMap() :

public class TreeMap<K,V> {
    public TreeMap() {
        comparator = null;
    }
    public TreeMap(Comparator<? super K> comparator) {
        this.comparator = comparator;
    }
    public TreeMap(Map<? extends K, ? extends V> m) {
        comparator = null;
        putAll(m);
    }
}

TreeMap.put() :

  目前不清楚TreeMap内部的二叉树到底是哪一种二叉树, 希望分析完put()以后能够确定TreeMap内部二叉树的结构;

public class TreeMap<K,V> {
    public V put(K key, V value) {
        Entry<K,V> t = root;
        if (t == null) {
            compare(key, key); 
            root = new Entry<>(key, value, null);
            size = 1;
            modCount++;
            return null;
        }
        int cmp;
        Entry<K,V> parent;
        Comparator<? super K> cpr = comparator;
        if (cpr != null) {...}
        else {
            Comparable<? super K> k = (Comparable<? super K>) key;
            do {
                parent = t;
                cmp = k.compareTo(t.key);
                if (cmp < 0)
                    t = t.left;
                else if (cmp > 0)
                    t = t.right;
            } while (t != null);
        }
        Entry<K,V> e = new Entry<>(key, value, parent);
        if (cmp < 0)
            parent.left = e;
        else
            parent.right = e;
        fixAfterInsertion(e);
        size++;
        modCount++;
        return null;
    }
}

  我们假设在插入元素时, cpr.compare(key, t.key)始终!=0, 并且cmp < 0与 cmp > 0交替进行;
  1、插入第一个元素时, root = null, 然后root = Entry;
  2、插入第二个元素时, 此时parent = t = root = Entry_01, 进入do...while中, t = t.left => t = null, parent.left = e => Entry02 = e = parent.left;
下图表示连续插入两个元素的过程:

第一次插入元素Entry01.png

插入第二个元素Entry02且cmp<0.png