C#中Hashtable与Dictionary的用法对比及选择

// Hashtable 示例
Hashtable hashtable = new Hashtable();
hashtable.Add(1, "one"); // 键是 int 类型，值是 string 类型
hashtable.Add("key", 42); // 键是 string 类型，值是 int 类型
// 需要类型转换来检索值
string value1 = (string)hashtable[1];
int value2 = (int)hashtable["key"];

// Dictionary 示例
Dictionary<int, string> dictionary = new Dictionary<int, string>();
dictionary.Add(1, "one"); // 键和值类型明确指定
string valFromDict = dictionary[1]; // 不需要类型转换

// Hashtable 无序性示例
Hashtable unorderedHashtable = new Hashtable();
unorderedHashtable.Add("a", 1);
unorderedHashtable.Add("b", 2);
unorderedHashtable.Add("c", 3);
// 遍历顺序可能不是 "a", "b", "c"
foreach (DictionaryEntry entry in unorderedHashtable)
{
    Console.WriteLine($"{entry.Key}: {entry.Value}");
}

// Dictionary 有序性示例
Dictionary<string, int> orderedDictionary = new Dictionary<string, int>();
orderedDictionary.Add("a", 1);
orderedDictionary.Add("b", 2);
orderedDictionary.Add("c", 3);
// 遍历顺序将是 "a", "b", "c"
foreach (KeyValuePair<string, int> kvp in orderedDictionary)
{
    Console.WriteLine($"{kvp.Key}: {kvp.Value}");
}

// Hashtable 允许 null 键和值示例
Hashtable hashtableWithNulls = new Hashtable();
hashtableWithNulls.Add(null, "nullValue");
hashtableWithNulls.Add("nullKey", null);

// Dictionary 不允许 null 键和值示例
try
{
    Dictionary<string, string> dictionaryWithNoNulls = new Dictionary<string, string>();
    dictionaryWithNoNulls.Add(null, "this will throw an exception"); // 将抛出 ArgumentNullException
}
catch (ArgumentNullException ex)
{
    Console.WriteLine(ex.Message); // 输出错误信息
}