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Hashtable Constructor (Int32, Single, IEqualityComparer)

Initializes a new, empty instance of the Hashtable class using the specified initial capacity, load factor, and IEqualityComparer object.

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

new : 
        capacity:int * 
        loadFactor:float32 * 
        equalityComparer:IEqualityComparer -> Hashtable

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.

equalityComparer
Type: System.Collections.IEqualityComparer

The IEqualityComparer object that defines the hash code provider and the comparer to use with the Hashtable.

-or-

a null reference (Nothing in Visual Basic) to use the default hash code provider and the default comparer. The default hash code provider is each key's implementation of Object.GetHashCode and the default comparer 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 IEqualityComparer object includes both the hash code provider and the comparer. If an IEqualityComparer is used in the Hashtable constructor, the objects used as keys in the Hashtable are not required to override the Object.GetHashCode and Object.Equals methods.

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 IEqualityComparer enables 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.

No code example is currently available or this language may not be supported.

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 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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