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Hashtable Constructor (Int32, Single, IHashCodeProvider, IComparer)

Note: This API is now obsolete.

Initializes a new, empty instance of the Hashtable class using the specified initial capacity, load factor, hash code provider, and comparer.

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

[ObsoleteAttribute(L"Please use Hashtable(int, float, IEqualityComparer) instead.")]
public:
Hashtable(
	int capacity, 
	float loadFactor, 
	IHashCodeProvider^ hcp, 
	IComparer^ comparer
)

Parameters

capacity
Type: System::Int32

The approximate number of elements that the Hashtable object can initially contain.

loadFactor
Type: System::Single

A number in the range from 0.1 through 1.0 that is multiplied by the default value which provides the best performance. The result is the maximum ratio of elements to buckets.

hcp
Type: System.Collections::IHashCodeProvider

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

-or-

nullptr to use the default hash code provider, which is each key's implementation of Object::GetHashCode.

comparer
Type: System.Collections::IComparer

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

-or-

nullptr to use the default comparer, which is each key's implementation of Object::Equals.

ExceptionCondition
ArgumentOutOfRangeException

capacity is less than zero.

-or-

loadFactor is less than 0.1.

-or-

loadFactor is greater than 1.0.

Specifying the initial capacity eliminates the need to perform a number of resizing operations while adding elements to the Hashtable object. 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. A load factor of 1.0 is the best balance between speed and size.

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. 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.

This constructor is an O(n) operation, where n is the capacity 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 namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myCultureComparer : public IEqualityComparer
{
public:
    CaseInsensitiveComparer^ myComparer;

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

public:
    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

public:
    virtual bool Equals(Object^ x, Object^ y)
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

public:
    virtual int GetHashCode(Object^ obj)
    {
        // Compare the hash code for the lowercase versions of the strings. 
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

public ref class SamplesHashtable
{

public:
	static void Main()
	{
        // Create a hash table using the default comparer.
        Hashtable^ myHT1 = gcnew Hashtable(3, (float).8);
        myHT1->Add("FIRST", "Hello");
        myHT1->Add("SECOND", "World");
        myHT1->Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses 
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable^ myHT2 = gcnew Hashtable(3, (float).8, gcnew myCultureComparer());
        myHT2->Add("FIRST", "Hello");
        myHT2->Add("SECOND", "World");
        myHT2->Add("THIRD", "!");

        // 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 = gcnew CultureInfo("tr-TR");
        Hashtable^ myHT3 = gcnew Hashtable(3, (float).8, gcnew myCultureComparer(myCul));
        myHT3->Add("FIRST", "Hello");
        myHT3->Add("SECOND", "World");
        myHT3->Add("THIRD", "!");

        // 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"));

	}
};

int main()
{
	SamplesHashtable::Main();
}

/* 
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

*/

.NET Framework

Supported in: 1.1, 1.0
Obsolete (compiler warning) in 4.6
Obsolete (compiler warning) in 4.5
Obsolete (compiler warning) in 4.5.1
Obsolete (compiler warning) in 4.5.2
Obsolete (compiler warning) in 4
Obsolete (compiler warning) in 3.5
Obsolete (compiler warning) in 3.5 SP1
Obsolete (compiler warning) in 3.0
Obsolete (compiler warning) in 3.0 SP1
Obsolete (compiler warning) in 3.0 SP2
Obsolete (compiler warning) in 2.0
Obsolete (compiler warning) in 2.0 SP1
Obsolete (compiler warning) in 2.0 SP2

.NET Framework Client Profile

Obsolete (compiler warning) in 4
Obsolete (compiler warning) in 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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