java - TreeMap 的先决条件

Question

就像要将对象插入到 HashMap 中一样，对象应该实现 equals() 和 hashcode() 方法(不一定)。 将对象插入 TreeMap 是否有任何特殊条件？

Answer 1

除非 Comparator在 TreeMap 的构造函数中提供了相互比较键的方法，键必须实现 Comparable .

有关 TreeMap 构造函数的更多信息，请参阅 javadoc:http://download.oracle.com/javase/6/docs/api/java/util/TreeMap.html

编辑:作为@MeBigFatGuy指出强烈建议 key 覆盖 equals()同样，以实现与比较一致的方式。来自 TreeMap javadoc:

Note that the ordering maintained by a sorted map (whether or not an explicit comparator is provided) must be consistent with equals if this sorted map is to correctly implement the Map interface. (See Comparable or Comparator for a precise definition of consistent with equals.) This is so because the Map interface is defined in terms of the equals operation, but a map performs all key comparisons using its compareTo (or compare) method, so two keys that are deemed equal by this method are, from the standpoint of the sorted map, equal. The behavior of a sorted map is well-defined even if its ordering is inconsistent with equals; it just fails to obey the general contract of the Map interface.