1.     //默认构造函数，按照key的自然顺序排列
    2.     // 如果key是自定义类，必须实现Comparable接口
    3.     public TreeMap() {
    4.         comparator = null;
    5.     }
    1.     //传递Comparator具体实现，按照该实现规则进行排序    
    2.     public TreeMap(Comparator<? super K> comparator) {
    3.         this.comparator = comparator;
    4.     }
    1. public TreeMap(Map<? extends K, ? extends V> m) {
    2.         comparator = null;
    3.         putAll(m);
    4.     }
    1. public TreeMap(SortedMap<K, ? extends V> m) {
    2.         comparator = m.comparator();
    3.         try {
    4.             buildFromSorted(m.size(), m.entrySet().iterator(), null, null);
    5.         } catch (java.io.IOException cannotHappen) {
    6.         } catch (ClassNotFoundException cannotHappen) {
    7.         }
    8.     }