HashTable in C# with Example
Hashtable is used to store a collection of
key/value pairs of different data
types and are organized based on the hash code of the key.
Generally, the hashtable object will contain buckets to store elements of the collection. The bucket here, is a virtual subgroup of elements within the hashtable and each bucket is associated with a hash code, which is generated based on the key of an element.
In C#, hashtable is same as a dictionary object but the only difference is that the dictionary object is used to store a key-value pair of same data type elements.
When compared with dictionary object, the hashtable will provide a lower performance because the hashtable elements are of object type so the boxing and unboxing process will occur when we are storing or retrieving values from the hashtable.
C# HashTable Declaration
Hashtable is a
non-generic type of collection so we can store a key/value pair elements
of different data
types and it is provided by System.Collections namespace.
As discussed earlier, the collection is a class so to define a hashtable, you just need to declare an instance of the hashtable class before we perform any operations like add, delete, etc.
HashTable Properties
The following are some of the commonly
used properties of hashtable in C#.
|
Property |
Description |
|
Count |
It is used to get the number of key/value pair elements in the
hashtable. |
|
IsFixedSize |
It is used to get a value to indicate that the hashtable has
fixed size or not. |
|
IsReadOnly |
It is used to get a value to indicate that the hashtable is
read-only or not. |
|
Item |
It is used to get or set the value associated with the
specified key. |
|
IsSynchronized |
It is used to get a value to indicate that access to hashtable
is synchronized (thread-safe) or not. |
|
Keys |
It is used to get the collection of keys in the hashtable. |
|
Values |
It is used to get the collection of values in the hashtable. |
HashTable Methods
The following are some of the commonly used methods of hashtable to perform
operations like add, delete, etc. on elements of hashtable in C#.
|
Method |
Description |
|
Add |
It is used to add an element with a specified key and value in
a hashtable. |
|
Clear |
It will remove all the elements from the hashtable. |
|
Clone |
It will create a shallow copy of hashtable. |
|
Contains |
It is useful to determine whether the hashtable contains a
specific key or not. |
|
ContainsKey |
It is useful to determine whether the hashtable contains a
specific key or not. |
|
ContainsValue |
It is useful to determine whether the hashtable contains a
specific value or not. |
|
Remove |
It is useful to remove an element with a specified key from
the hashtable. |
|
GetHash |
It is useful to get the hash code for the specified key. |
Adding Elements to HashTable
While adding elements to hashtable we need to make sure that
there will be no any duplicate keys because hashtable will allow us to store
duplicate values but keys must be unique to identify the values in the hashtable.
In hashtable, we can add a key/value pair elements of different data types as ca be seen in the following example
using C#.
using System;
using System.Collections;
namespace CsharpnaijaTutorial
{
class Program
{
static void Main(string[] args)
{
Hashtable hashTable = new Hashtable();
hashTable.Add("message", "Welcome");
hashTable.Add("web site", "Csharp naija");
hashTable.Add(1, 20.5);
hashTable.Add(2, null);
// Another way
to add elements. If key not exist, then that key adds a new key/value pair.
hashTable [3] = "Tutorials";
// Add method
will throws an exception if key already exists in hash table
try
{
hashTable.Add(2, 100);
}
catch
{
Console.WriteLine("An element with Key = '2'
already exists.");
}
Console.WriteLine("*********HashTable
Elements********");
// It will
return elements as KeyValuePair objects.
foreach (DictionaryEntry
item in hashTable)
{
Console.WriteLine("Key = {0}, Value = {1}", item.Key, item.Value);
}
Console.ReadLine();
}
}
}
From above example, we
created a new hastable (hashTable) and adding a
different data type elements (key/value) to hashtable (hashTable) in different ways. As discussed, Add method will throw an exception in case if we try to add
a key (2) which is already existing so to handle that exception we
used a try-catch block as can be seen in the output below.
Removing Elements from HashTable
In C#, you can delete elements from
hashtable by using the Remove() method.
The following example shows how to use the delete method to delete elements
from hashtable.
using System;
using System.Collections;
namespace CsharpnaijaTutorial
{
class Program
{
static void Main(string[] args)
{
Hashtable htbl = new Hashtable();
htbl.Add("message", "Welcome");
htbl.Add("website", "Csharp naija");
htbl.Add(1, 20.5f);
htbl.Add(2, 10);
htbl.Add(3, 100);
// Removing
hashtable elements with keys
htbl.Remove(1);
htbl.Remove("msg");
Console.WriteLine("*********HashTable
Elements********");
foreach (DictionaryEntry
item in htbl)
{
Console.WriteLine("Key = {0}, Value = {1}", item.Key, item.Value);
}
Console.ReadLine();
}
}
}
We use the Remove method to delete the first and the
second elements in the hashtable collection as shown in the image below.
Check If Element Exists
By using Contains(), ContainsKey() and ContainsValue() methods, we can
check whether the specified element exists in hashtable or not. In case, if it
exists these methods will return true otherwise false.
The following is the example of using Contains(),
ContainsKey() and ContainsValue() methods to
check for an item that exists in a hashtable or not in C#.
using System;
using System.Collections;
namespace CsharpnaijaTutorial
{
class Program
{
static void Main(string[] args)
{
Hashtable htbl = new Hashtable();
htbl.Add("message", "Welcome");
htbl.Add("website", "Csharp naija");
htbl.Add(1, 20.5f);
htbl.Add(2, 10);
htbl.Add(3, 100);
Console.WriteLine("Contains Key 4: {0}", htbl.Contains(4));
Console.WriteLine("Contains Key 2: {0}", htbl.ContainsKey(2));
Console.WriteLine("Contains Value 'Csharp
naija': {0}", htbl.ContainsValue("Csharp naija"));
Console.ReadLine();
}
}
}
From above example, we used a Contains(),
ContainsKey() and ContainsValue() methods to
check for a particular keys and values exists in hashtable (htbl) or not as can
be seen from the the output screen shown below.
Thank you
References
1.
Tutlane
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