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Hashtable.Hashtable(IDictionary, IHashCodeProvider, IComparer) Constructor

NOTE: This constructor is now obsolete.

Initializes a new instance of the Hashtable class by copying the elements from the specified dictionary to the new Hashtable object. The new Hashtable object has an initial capacity equal to the number of elements copied, and uses the default load factor, and the specified hash code provider and comparer.

Namespace: System.Collections
Assembly: mscorlib (in mscorlib.dll)

[ObsoleteAttribute("Please use Hashtable(IDictionary, IEqualityComparer) instead.")] 
public Hashtable (
	IDictionary d,
	IHashCodeProvider hcp,
	IComparer comparer
)
/** @attribute ObsoleteAttribute("Please use Hashtable(IDictionary, IEqualityComparer) instead.") */ 
public Hashtable (
	IDictionary d, 
	IHashCodeProvider hcp, 
	IComparer comparer
)
ObsoleteAttribute("Please use Hashtable(IDictionary, IEqualityComparer) instead.") 
public function Hashtable (
	d : IDictionary, 
	hcp : IHashCodeProvider, 
	comparer : IComparer
)
Not applicable.

Parameters

d

The IDictionary object to copy to a new Hashtable object.

hcp

The IHashCodeProvider object that supplies the hash codes for all keys in the Hashtable.

-or-

a null reference (Nothing in Visual Basic) to use the default hash code provider, which is each key's implementation of Object.GetHashCode.

comparer

The IComparer object to use to determine whether two keys are equal.

-or-

a null reference (Nothing in Visual Basic) to use the default comparer, which is each key's implementation of Object.Equals.

Exception typeCondition

ArgumentNullException

d is a null reference (Nothing in Visual Basic).

The initial capacity is set to the number of elements in the source dictionary. Capacity is automatically increased as required based on the load factor.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The hash code provider dispenses hash codes for keys in the Hashtable object. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

The custom hash code provider and the custom comparer enable scenarios such as doing lookups with case-insensitive strings.

The elements of the new Hashtable are sorted in the same order in which the enumerator iterates through the IDictionary object.

This constructor is an O(n) operation, where n is the number of elements in the d parameter.

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using System;
using System.Collections;
using System.Globalization;

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        if (myComparer.Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public int GetHashCode(object obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create the dictionary.
        SortedList mySL = new SortedList();
        mySL.Add("FIRST", "Hello");
        mySL.Add("SECOND", "World");
        mySL.Add("THIRD", "!");

        // Create a hash table using the default comparer.
        Hashtable myHT1 = new Hashtable(mySL);

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable myHT2 = new Hashtable(mySL, new myCultureComparer());

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo myCul = new CultureInfo("tr-TR");
        Hashtable myHT3 = new Hashtable(mySL, new myCultureComparer(myCul));

        // Search for a key in each hash table.
        Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"));
        Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"));
        Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"));

    }

}


/* 
This code produces the following output. 
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/


Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 1.0, 1.1, 2.0
Obsolete (compiler warning) in 3.0

.NET Compact Framework

Supported in: 1.0
Obsolete (compiler warning) in 2.0

XNA Framework

Supported in: 1.0

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