C# |获取或设置哈希表
中与指定键关联的值
原文:https://www . geesforgeks . org/c-sharp-get-or-set-value-associated-in-specified-key-in-hashtable/
哈希表。项目【对象】属性 用于获取或设置 哈希表 中指定键的关联值。
语法:
public virtual object this[object key] { get; set; }
这里键是取值或设置值的对象类型的键。
异常:
- 参数空异常:如果键为空。
- notSupportDexception:如果设置了属性并且哈希表是只读的。或者设置了属性，键在集合中不存在，哈希表有固定的大小。
注:
- 此属性返回与特定键关联的值。如果找不到该键，并且有人试图获取该键，则该属性将返回 null，如果试图设置，将导致创建具有指定键的新元素。
- 检索和设置该属性的值是一个 O(1)操作。
以下程序说明了上述属性的使用:
例 1:
// C# code to Gets or sets the value
// associated with the specified key
using System;
using System.Collections;
class GFG {
// Driver code
public static void Main()
{
// Creating a Hashtable
Hashtable myTable = new Hashtable();
// Adding elements in Hashtable
myTable.Add("g", "geeks");
myTable.Add("c", "c++");
myTable.Add("d", "data structures");
myTable.Add("q", "quiz");
// Get a collection of the keys.
ICollection c = myTable.Keys;
// Displaying the contents
foreach(string str in c)
Console.WriteLine(str + ": " + myTable[str]);
// Setting the value associated with key "c"
myTable["c"] = "C#";
Console.WriteLine("Updated Values:");
// Displaying the contents
foreach(string str in c)
Console.WriteLine(str + ": " + myTable[str]);
}
}
Output:
d: data structures
c: c++
q: quiz
g: geeks
Updated Values:
d: data structures
c: C#
q: quiz
g: geeks
例 2:
// C# code to Gets or sets the value
// associated with the specified key
using System;
using System.Collections;
class GFG {
// Driver code
public static void Main()
{
// Creating a Hashtable
Hashtable myTable = new Hashtable();
// Adding elements in Hashtable
myTable.Add("4", "Even");
myTable.Add("9", "Odd");
myTable.Add("5", "Odd and Prime");
myTable.Add("2", "Even and Prime");
// Get a collection of the keys.
ICollection c = myTable.Keys;
// Displaying the contents
foreach(string str in c)
Console.WriteLine(str + ": " + myTable[str]);
// Setting the value associated
// with key "56" which is not present
// will result in the creation of
// new key and value will be set which
// is given by the user
myTable["56"] = "New Value";
Console.WriteLine("Updated Values:");
// Displaying the contents
foreach(string str in c)
Console.WriteLine(str + ": " + myTable[str]);
}
}
Output:
5: Odd and Prime
9: Odd
2: Even and Prime
4: Even
Updated Values:
5: Odd and Prime
9: Odd
2: Even and Prime
56: New Value
4: Even
参考:
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