Hashtable Class

Namespace: System.Collections

Assembly: System.Collections.dll

Summary

Represents a collection of keys and values that are organized based on the hash code of the key. It provides fast lookups and is thread-safe for a single writer with multiple readers.

Syntax

public class Hashtable : IDictionary, ICollection, IEnumerable, ISerializable, IDeserializationCallback, ICloneable

Constructors

Signature	Description
`Hashtable()`	Initializes a new empty hashtable with the default load factor and capacity.
`Hashtable(int capacity)`	Initializes a new empty hashtable with the specified initial capacity.
`Hashtable(IEqualityComparer? comparer)`	Initializes a new empty hashtable that uses the specified `IEqualityComparer`.
`Hashtable(IDictionary d)`	Initializes a new hashtable containing elements copied from the specified dictionary.
`Hashtable(IDictionary d, IHashCodeProvider? hcp, IComparer? comparer)`	Initializes a new hashtable with a custom hash code provider and comparer.

Properties

Name	Type	Description
`Count`	`int`	Gets the number of key/value pairs contained in the `Hashtable`.
`IsReadOnly`	`bool`	Indicates whether the `Hashtable` is read-only.
`IsFixedSize`	`bool`	Indicates whether the `Hashtable` has a fixed size.
`Keys`	`ICollection`	Gets an `ICollection` containing the keys in the `Hashtable`.
`Values`	`ICollection`	Gets an `ICollection` containing the values in the `Hashtable`.
`Comparer`	`IEqualityComparer`	Gets the `IEqualityComparer` object that compares keys for the `Hashtable`.
`SyncRoot`	`object`	Gets an object that can be used to synchronize access.
`IsSynchronized`	`bool`	Indicates whether access to the `Hashtable` is synchronized (thread safe).

Methods

Signature	Description
`void Add(object key, object? value)`	Adds an element with the specified key and value.
`bool Contains(object key)`	Determines whether the `Hashtable` contains a specific key.
`void Clear()`	Removes all elements from the `Hashtable`.
`object? this[object key] { get; set; }`	Gets or sets the value associated with the specified key.
`IDictionaryEnumerator GetEnumerator()`	Returns an enumerator that iterates through the `Hashtable`.
`bool Remove(object key)`	Removes the element with the specified key.
`void Clone()`	Creates a shallow copy of the `Hashtable`.
`void GetObjectData(SerializationInfo info, StreamingContext context)`	Implements the `ISerializable` interface and populates a `SerializationInfo` with the data needed to serialize the target object.
`void OnDeserialization(object? sender)`	Implements the `IDeserializationCallback` interface and raises the deserialization event when the entire object graph has been deserialized.
`static bool Synchronized(Hashtable table)`	Returns a synchronized (thread-safe) wrapper for the `Hashtable`.

Examples

using System;
using System.Collections;

class Program
{
    static void Main()
    {
        Hashtable ht = new Hashtable();

        // Adding key/value pairs
        ht.Add("Apple", 1);
        ht.Add("Banana", 2);
        ht["Cherry"] = 3;

        // Retrieve a value
        Console.WriteLine($"Apple = {ht["Apple"]}");

        // Iterate through the Hashtable
        foreach (DictionaryEntry entry in ht)
        {
            Console.WriteLine($"Key = {entry.Key}, Value = {entry.Value}");
        }

        // Check for a key
        if (ht.ContainsKey("Banana"))
            Console.WriteLine("Banana is present.");
    }
}