Hashtable 类
定义
重要
一些信息与预发行产品相关，相应产品在发行之前可能会进行重大修改。 对于此处提供的信息，Microsoft 不作任何明示或暗示的担保。
表示根据键的哈希代码进行组织的键/值对的集合。
public ref class Hashtable : System::Collections::IDictionarypublic ref class Hashtable : ICloneable, System::Collections::IDictionary, System::Runtime::Serialization::IDeserializationCallback, System::Runtime::Serialization::ISerializablepublic class Hashtable : System.Collections.IDictionarypublic class Hashtable : ICloneable, System.Collections.IDictionary, System.Runtime.Serialization.IDeserializationCallback, System.Runtime.Serialization.ISerializable[System.Serializable]
public class Hashtable : ICloneable, System.Collections.IDictionary, System.Runtime.Serialization.IDeserializationCallback, System.Runtime.Serialization.ISerializable[System.Serializable]
[System.Runtime.InteropServices.ComVisible(true)]
public class Hashtable : ICloneable, System.Collections.IDictionary, System.Runtime.Serialization.IDeserializationCallback, System.Runtime.Serialization.ISerializabletype Hashtable = class
interface ICollection
interface IEnumerable
interface IDictionarytype Hashtable = class
interface ICollection
interface IEnumerable
interface IDictionary
interface ICloneable
interface IDeserializationCallback
interface ISerializabletype Hashtable = class
interface ICollection
interface IEnumerable
interface IDictionary
interface ISerializable
interface IDeserializationCallback
interface ICloneable[<System.Serializable>]
type Hashtable = class
interface IDictionary
interface ICollection
interface IEnumerable
interface ISerializable
interface IDeserializationCallback
interface ICloneable[<System.Serializable>]
[<System.Runtime.InteropServices.ComVisible(true)>]
type Hashtable = class
interface IDictionary
interface ICollection
interface IEnumerable
interface ISerializable
interface IDeserializationCallback
interface ICloneablePublic Class Hashtable
Implements IDictionaryPublic Class Hashtable
Implements ICloneable, IDeserializationCallback, IDictionary, ISerializable- 继承
-
Hashtable
- 派生
- 属性
- 实现
示例
以下示例演示如何创建、初始化和对 执行各种函数， Hashtable 以及如何打印出其键和值。
using namespace System;
using namespace System::Collections;
public ref class Example
{
public:
static void Main()
{
// Create a new hash table.
//
Hashtable^ openWith = gcnew Hashtable();
// Add some elements to the hash table. There are no
// duplicate keys, but some of the values are duplicates.
openWith->Add("txt", "notepad.exe");
openWith->Add("bmp", "paint.exe");
openWith->Add("dib", "paint.exe");
openWith->Add("rtf", "wordpad.exe");
// The Add method throws an exception if the new key is
// already in the hash table.
try
{
openWith->Add("txt", "winword.exe");
}
catch(...)
{
Console::WriteLine("An element with Key = \"txt\" already exists.");
}
// The Item property is the default property, so you
// can omit its name when accessing elements.
Console::WriteLine("For key = \"rtf\", value = {0}.", openWith["rtf"]);
// The default Item property can be used to change the value
// associated with a key.
openWith["rtf"] = "winword.exe";
Console::WriteLine("For key = \"rtf\", value = {0}.", openWith["rtf"]);
// If a key does not exist, setting the default Item property
// for that key adds a new key/value pair.
openWith["doc"] = "winword.exe";
// ContainsKey can be used to test keys before inserting
// them.
if (!openWith->ContainsKey("ht"))
{
openWith->Add("ht", "hypertrm.exe");
Console::WriteLine("Value added for key = \"ht\": {0}", openWith["ht"]);
}
// When you use foreach to enumerate hash table elements,
// the elements are retrieved as KeyValuePair objects.
Console::WriteLine();
for each( DictionaryEntry de in openWith )
{
Console::WriteLine("Key = {0}, Value = {1}", de.Key, de.Value);
}
// To get the values alone, use the Values property.
ICollection^ valueColl = openWith->Values;
// The elements of the ValueCollection are strongly typed
// with the type that was specified for hash table values.
Console::WriteLine();
for each( String^ s in valueColl )
{
Console::WriteLine("Value = {0}", s);
}
// To get the keys alone, use the Keys property.
ICollection^ keyColl = openWith->Keys;
// The elements of the KeyCollection are strongly typed
// with the type that was specified for hash table keys.
Console::WriteLine();
for each( String^ s in keyColl )
{
Console::WriteLine("Key = {0}", s);
}
// Use the Remove method to remove a key/value pair.
Console::WriteLine("\nRemove(\"doc\")");
openWith->Remove("doc");
if (!openWith->ContainsKey("doc"))
{
Console::WriteLine("Key \"doc\" is not found.");
}
}
};
int main()
{
Example::Main();
}
/* This code example produces the following output:
An element with Key = "txt" already exists.
For key = "rtf", value = wordpad.exe.
For key = "rtf", value = winword.exe.
Value added for key = "ht": hypertrm.exe
Key = dib, Value = paint.exe
Key = txt, Value = notepad.exe
Key = ht, Value = hypertrm.exe
Key = bmp, Value = paint.exe
Key = rtf, Value = winword.exe
Key = doc, Value = winword.exe
Value = paint.exe
Value = notepad.exe
Value = hypertrm.exe
Value = paint.exe
Value = winword.exe
Value = winword.exe
Key = dib
Key = txt
Key = ht
Key = bmp
Key = rtf
Key = doc
Remove("doc")
Key "doc" is not found.
*/
using System;
using System.Collections;
class Example
{
public static void Main()
{
// Create a new hash table.
//
Hashtable openWith = new Hashtable();
// Add some elements to the hash table. There are no
// duplicate keys, but some of the values are duplicates.
openWith.Add("txt", "notepad.exe");
openWith.Add("bmp", "paint.exe");
openWith.Add("dib", "paint.exe");
openWith.Add("rtf", "wordpad.exe");
// The Add method throws an exception if the new key is
// already in the hash table.
try
{
openWith.Add("txt", "winword.exe");
}
catch
{
Console.WriteLine("An element with Key = \"txt\" already exists.");
}
// The Item property is the default property, so you
// can omit its name when accessing elements.
Console.WriteLine("For key = \"rtf\", value = {0}.", openWith["rtf"]);
// The default Item property can be used to change the value
// associated with a key.
openWith["rtf"] = "winword.exe";
Console.WriteLine("For key = \"rtf\", value = {0}.", openWith["rtf"]);
// If a key does not exist, setting the default Item property
// for that key adds a new key/value pair.
openWith["doc"] = "winword.exe";
// ContainsKey can be used to test keys before inserting
// them.
if (!openWith.ContainsKey("ht"))
{
openWith.Add("ht", "hypertrm.exe");
Console.WriteLine("Value added for key = \"ht\": {0}", openWith["ht"]);
}
// When you use foreach to enumerate hash table elements,
// the elements are retrieved as KeyValuePair objects.
Console.WriteLine();
foreach( DictionaryEntry de in openWith )
{
Console.WriteLine("Key = {0}, Value = {1}", de.Key, de.Value);
}
// To get the values alone, use the Values property.
ICollection valueColl = openWith.Values;
// The elements of the ValueCollection are strongly typed
// with the type that was specified for hash table values.
Console.WriteLine();
foreach( string s in valueColl )
{
Console.WriteLine("Value = {0}", s);
}
// To get the keys alone, use the Keys property.
ICollection keyColl = openWith.Keys;
// The elements of the KeyCollection are strongly typed
// with the type that was specified for hash table keys.
Console.WriteLine();
foreach( string s in keyColl )
{
Console.WriteLine("Key = {0}", s);
}
// Use the Remove method to remove a key/value pair.
Console.WriteLine("\nRemove(\"doc\")");
openWith.Remove("doc");
if (!openWith.ContainsKey("doc"))
{
Console.WriteLine("Key \"doc\" is not found.");
}
}
}
/* This code example produces the following output:
An element with Key = "txt" already exists.
For key = "rtf", value = wordpad.exe.
For key = "rtf", value = winword.exe.
Value added for key = "ht": hypertrm.exe
Key = dib, Value = paint.exe
Key = txt, Value = notepad.exe
Key = ht, Value = hypertrm.exe
Key = bmp, Value = paint.exe
Key = rtf, Value = winword.exe
Key = doc, Value = winword.exe
Value = paint.exe
Value = notepad.exe
Value = hypertrm.exe
Value = paint.exe
Value = winword.exe
Value = winword.exe
Key = dib
Key = txt
Key = ht
Key = bmp
Key = rtf
Key = doc
Remove("doc")
Key "doc" is not found.
*/
Imports System.Collections
Module Example
Sub Main()
' Create a new hash table.
'
Dim openWith As New Hashtable()
' Add some elements to the hash table. There are no
' duplicate keys, but some of the values are duplicates.
openWith.Add("txt", "notepad.exe")
openWith.Add("bmp", "paint.exe")
openWith.Add("dib", "paint.exe")
openWith.Add("rtf", "wordpad.exe")
' The Add method throws an exception if the new key is
' already in the hash table.
Try
openWith.Add("txt", "winword.exe")
Catch
Console.WriteLine("An element with Key = ""txt"" already exists.")
End Try
' The Item property is the default property, so you
' can omit its name when accessing elements.
Console.WriteLine("For key = ""rtf"", value = {0}.", _
openWith("rtf"))
' The default Item property can be used to change the value
' associated with a key.
openWith("rtf") = "winword.exe"
Console.WriteLine("For key = ""rtf"", value = {0}.", _
openWith("rtf"))
' If a key does not exist, setting the default Item property
' for that key adds a new key/value pair.
openWith("doc") = "winword.exe"
' ContainsKey can be used to test keys before inserting
' them.
If Not openWith.ContainsKey("ht") Then
openWith.Add("ht", "hypertrm.exe")
Console.WriteLine("Value added for key = ""ht"": {0}", _
openWith("ht"))
End If
' When you use foreach to enumerate hash table elements,
' the elements are retrieved as KeyValuePair objects.
Console.WriteLine()
For Each de As DictionaryEntry In openWith
Console.WriteLine("Key = {0}, Value = {1}", _
de.Key, de.Value)
Next de
' To get the values alone, use the Values property.
Dim valueColl As ICollection = openWith.Values
' The elements of the ValueCollection are strongly typed
' with the type that was specified for hash table values.
Console.WriteLine()
For Each s As String In valueColl
Console.WriteLine("Value = {0}", s)
Next s
' To get the keys alone, use the Keys property.
Dim keyColl As ICollection = openWith.Keys
' The elements of the KeyCollection are strongly typed
' with the type that was specified for hash table keys.
Console.WriteLine()
For Each s As String In keyColl
Console.WriteLine("Key = {0}", s)
Next s
' Use the Remove method to remove a key/value pair.
Console.WriteLine(vbLf + "Remove(""doc"")")
openWith.Remove("doc")
If Not openWith.ContainsKey("doc") Then
Console.WriteLine("Key ""doc"" is not found.")
End If
End Sub
End Module
' This code example produces the following output:
'
'An element with Key = "txt" already exists.
'For key = "rtf", value = wordpad.exe.
'For key = "rtf", value = winword.exe.
'Value added for key = "ht": hypertrm.exe
'
'Key = dib, Value = paint.exe
'Key = txt, Value = notepad.exe
'Key = ht, Value = hypertrm.exe
'Key = bmp, Value = paint.exe
'Key = rtf, Value = winword.exe
'Key = doc, Value = winword.exe
'
'Value = paint.exe
'Value = notepad.exe
'Value = hypertrm.exe
'Value = paint.exe
'Value = winword.exe
'Value = winword.exe
'
'Key = dib
'Key = txt
'Key = ht
'Key = bmp
'Key = rtf
'Key = doc
'
'Remove("doc")
'Key "doc" is not found.
# Create new hash table using PowerShell syntax
$OpenWith = @{}
# Add one element to the hash table using the Add method
$OpenWith.Add('txt', 'notepad.exe')
# Add three eleements using PowerShell syntax three different ways
$OpenWith.dib = 'paint.exe'
$KeyBMP = 'bmp'
$OpenWith[$KeyBMP] = 'paint.exe'
$OpenWith += @{'rtf' = 'wordpad.exe'}
# Display hash table
"There are {0} in the `$OpenWith hash table as follows:" -f $OpenWith.Count
''
# Display hashtable properties
'Count of items in the hashtable : {0}' -f $OpenWith.Count
'Is hashtable fixed size? : {0}' -f $OpenWith.IsFixedSize
'Is hashtable read-only? : {0}' -f $OpenWith.IsReadonly
'Is hashtabale synchronised? : {0}' -f $OpenWith.IsSynchronized
''
'Keys in hashtable:'
$OpenWith.Keys
''
'Values in hashtable:'
$OpenWith.Values
''
<#
This script produces the following output:
There are 4 in the $OpenWith hash table as follows:
Name Value
---- -----
txt notepad.exe
dib paint.exe
bmp paint.exe
rtf wordpad.exe
Count of items in the hashtable : 4
Is hashtable fixed size? : False
Is hashtable read-only? : False
Is hashtabale synchronised? : False
Keys in hashtable:
txt
dib
bmp
rtf
Values in hashtable:
notepad.exe
paint.exe
paint.exe
wordpad.exe
#>
注解
每个元素都是存储在 对象中的 DictionaryEntry 键/值对。 键不能是 null，但值可以是 。
重要
不建议使用 Hashtable 类进行新开发。 建议改用 泛型 Dictionary<TKey,TValue> 类。 有关详细信息，请参阅 不应在 GitHub 上使用非泛型集合 。
需要由 Hashtable 用作键的对象来替代 Object.GetHashCode 方法 (或 IHashCodeProvider 接口) ， Object.Equals 方法 (或 IComparer 接口) 。 方法和接口的实现必须以相同的方式处理区分大小写：否则， Hashtable 的行为可能不正确。 例如，在创建 Hashtable时，必须将 CaseInsensitiveHashCodeProvider 类 (或任何不区分大小写 IHashCodeProvider 的实现) 与 CaseInsensitiveComparer 类 (或任何不区分大小写 IComparer 的实现) 。
此外，当键存在于 中 Hashtable时，使用相同参数调用时，这些方法必须生成相同的结果。 另一 Hashtable 种方法是将构造函数与 参数一 IEqualityComparer 起使用。 如果键相等性只是引用相等性，则 和 Object.Equals 的Object.GetHashCode继承实现就足够了。
键对象必须是不可变的，只要它们用作 中的 Hashtable键。
将 元素添加到 时， Hashtable会根据键的哈希代码将元素放入存储桶中。 密钥的后续查找使用密钥的哈希代码在一个特定存储桶中搜索，从而大大减少了查找元素所需的键比较次数。
的 Hashtable 负载因子确定元素与存储桶的最大比率。 较小的负载因子会导致平均查找时间更快，但代价是内存消耗增加。 默认负载因子 1.0 通常提供速度和大小之间的最佳平衡。 创建 时 Hashtable ，还可以指定不同的负载因子。
当元素添加到 时 Hashtable，的实际负载因子 Hashtable 会增加。 当实际负载因子达到指定的负载因子时，中的 Hashtable 存储桶数将自动增加到大于当前存储桶数两倍的 Hashtable 最小质数。
中的每个 Hashtable 键对象都必须提供其自己的哈希函数，可以通过调用 GetHash来访问该函数。 但是，任何对象实现 IHashCodeProvider 都可以传递给构造 Hashtable 函数，并且该哈希函数将用于表中的所有对象。
的 Hashtable 容量是 可以容纳的元素 Hashtable 数。 将元素添加到 时 Hashtable，容量会根据需要通过重新分配自动增加。
仅.NET Framework：对于非常大Hashtable的对象，可以通过在运行时环境中将配置元素的 <gcAllowVeryLargeObjects> 属性设置为 enabled ，将 64 位系统上的最大容量增加到 true 20 亿个元素。
foreach Visual Basic) 中 C# 语言 (For Each 语句返回集合中元素类型的 对象。 由于 的每个 Hashtable 元素都是键/值对，因此元素类型不是键的类型或值的类型。 相反，元素类型为 DictionaryEntry。 例如：
for each(DictionaryEntry de in myHashtable)
{
// ...
}
foreach(DictionaryEntry de in myHashtable)
{
// ...
}
For Each de As DictionaryEntry In myHashtable
' ...
Next de
语句 foreach 是枚举器的包装器，它只允许读取集合，而不允许写入集合。
由于序列化和反序列化 枚举器 Hashtable 可能会导致元素重新排序，因此如果不调用 Reset 方法，则无法继续枚举。
注意
由于密钥可以继承且其行为发生更改，因此使用 Equals 方法的比较无法保证其绝对唯一性。
构造函数
属性
| comparer |
已过时.
已过时.
|
| Count |
获取包含在 Hashtable 中的键/值对的数目。 |
| EqualityComparer |
获取要用于 IEqualityComparer 的 Hashtable。 |
| hcp |
已过时.
已过时.
获取或设置可分配哈希代码的对象。 |
| IsFixedSize |
获取一个值，该值指示 Hashtable 是否具有固定大小。 |
| IsReadOnly |
获取一个值，该值指示 Hashtable 是否为只读。 |
| IsSynchronized |
获取一个值，该值指示是否同步对 Hashtable 的访问（线程安全）。 |
| Item[Object] |
获取或设置与指定的键关联的值。 |
| Keys |
获取包含 ICollection 中的键的 Hashtable。 |
| SyncRoot |
获取可用于同步对 Hashtable 的访问的对象。 |
| Values |
获取一个 ICollection，它包含 Hashtable 中的值。 |
方法
| Add(Object, Object) |
将带有指定键和值的元素添加到 Hashtable 中。 |
| Clear() |
从 Hashtable 中移除所有元素。 |
| Clone() |
创建 Hashtable 的浅表副本。 |
| Contains(Object) |
确定 Hashtable 是否包含特定键。 |
| ContainsKey(Object) |
确定 Hashtable 是否包含特定键。 |
| ContainsValue(Object) |
确定 Hashtable 是否包含特定值。 |
| CopyTo(Array, Int32) | |
| Equals(Object) |
确定指定对象是否等于当前对象。 (继承自 Object) |
| GetEnumerator() |
返回循环访问 IDictionaryEnumerator 的 Hashtable。 |
| GetHash(Object) |
返回指定键的哈希代码。 |
| GetHashCode() |
作为默认哈希函数。 (继承自 Object) |
| GetObjectData(SerializationInfo, StreamingContext) |
已过时.
实现 ISerializable 接口，并返回序列化 Hashtable 所需的数据。 |
| GetType() |
获取当前实例的 Type。 (继承自 Object) |
| KeyEquals(Object, Object) | |
| MemberwiseClone() |
创建当前 Object 的浅表副本。 (继承自 Object) |
| OnDeserialization(Object) |
实现 ISerializable 接口，并在完成反序列化之后引发反序列化事件。 |
| Remove(Object) |
从 Hashtable 中移除包含指定键的元素。 |
| Synchronized(Hashtable) |
返回 Hashtable 的同步（线程安全）包装。 |
| ToString() |
返回表示当前对象的字符串。 (继承自 Object) |
显式接口实现
| IEnumerable.GetEnumerator() |
返回循环访问集合的枚举数。 |
扩展方法
| Cast<TResult>(IEnumerable) |
将 IEnumerable 的元素强制转换为指定的类型。 |
| OfType<TResult>(IEnumerable) |
根据指定类型筛选 IEnumerable 的元素。 |
| AsParallel(IEnumerable) |
启用查询的并行化。 |
| AsQueryable(IEnumerable) |
将 IEnumerable 转换为 IQueryable。 |
适用于
线程安全性
Hashtable 是线程安全，可供多个读取器线程和单个写入线程使用。 当只有一个线程执行写入 (更新) 操作时，它对于多线程使用是安全的，只要编写器序列化为 Hashtable即可进行无锁读取。 若要支持多个编写器， Hashtable 必须通过 方法返回 Synchronized(Hashtable) 的包装器对 执行的所有操作，前提是没有线程读取对象 Hashtable 。
通过集合枚举本质上不是线程安全的过程。 即使某个集合已同步，其他线程仍可以修改该集合，这会导致枚举数引发异常。 若要确保枚举过程中的线程安全性，可以在整个枚举期间锁定集合，或者捕获由其他线程进行的更改所导致的异常。
