private boolean searchWord(TrieNode2 _root, String _word) {	
		if(null == _root || null == _word || "".equals(_word))
			return false;
		char[] cs = _word.toCharArray();//将字符串转化为字符数组
		for(int i = 0; i < cs.length; i++){			
			int index;
			if(cs[i] >= 'A' && cs[i] <= 'Z'){
				index = cs[i]-'A';
			}
			else if(cs[i] >= 'a' && cs[i] <= 'z') 
				index = cs[i] - 'a';
			else
				return false;
			
			TrieNode2 child_node = _root._children[index];
			if(child_node == null) {
				return false;
			}
			else {
				_root = child_node;
			}				
		}
		
		return _root.isWord();
	}