Class HashMap<TKey, TValue>

A C# emulation of the Java Hashmap

A System.Collections.Generic.Dictionary`2 is a close equivalent to the Java Hashmap. One difference java implementation of the class is that the Hashmap supports both null keys and values, where the C# Dictionary only supports null values not keys. Also, V Get(TKey) method in Java returns null if the key doesn't exist, instead of throwing an exception. This implementation doesn't throw an exception when a key doesn't exist, it will return null. This class is slower than using a System.Collections.Generic.Dictionary`2, because of extra checks that have to be done on each access, to check for null.

NOTE: This class works best with nullable types. default(T) is returned when a key doesn't exist in the collection (this being similar to how Java returns null). Therefore, if the expected behavior of the java code is to execute code based on if the key exists, when the key is an integer type, it will return 0 instead of null.

Consider also implementing IDictionary, IEnumerable, and ICollection like System.Collections.Generic.Dictionary`2 does, so HashMap can be used in substituted in place for the same interfaces it implements.

Inheritance
System.Object
HashMap<TKey, TValue>
IdentityHashMap<TKey, TValue>
LinkedHashMap<TKey, TValue>
Implements
System.Collections.Generic.IDictionary<TKey, TValue>
System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey, TValue>>
System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey, TValue>>
System.Collections.IEnumerable
Inherited Members
System.Object.Equals(System.Object, System.Object)
System.Object.GetType()
System.Object.MemberwiseClone()
System.Object.ReferenceEquals(System.Object, System.Object)
Namespace: Lucene.Net.Support
Assembly: Lucene.Net.dll
Syntax
public class HashMap<TKey, TValue> : IDictionary<TKey, TValue>, ICollection<KeyValuePair<TKey, TValue>>, IEnumerable<KeyValuePair<TKey, TValue>>, IEnumerable
Type Parameters
Name Description
TKey

The type of keys in the dictionary
TValue

The type of values in the dictionary
Remarks

Unordered Dictionaries

  • System.Collections.Generic.Dictionary`2 - use when order is not important and all keys are non-null.
  • HashMap<TKey, TValue> - use when order is not important and support for a null key is required.

Ordered Dictionaries

  • LinkedHashMap<TKey, TValue> - use when you need to preserve entry insertion order. Keys are nullable.
  • System.Collections.Generic.SortedDictionary`2 - use when you need natural sort order. Keys must be unique.
  • TreeDictionary<K, V> - use when you need natural sort order. Keys may contain duplicates.
  • LurchTable<TKey, TValue> - use when you need to sort by most recent access or most recent update. Works well for LRU caching.

Constructors

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HashMap()

Declaration
public HashMap()
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HashMap(IEnumerable<KeyValuePair<TKey, TValue>>)

Declaration
public HashMap(IEnumerable<KeyValuePair<TKey, TValue>> other)
Parameters
Type Name Description
System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey, TValue>> other
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HashMap(IEqualityComparer<TKey>)

Declaration
public HashMap(IEqualityComparer<TKey> comparer)
Parameters
Type Name Description
System.Collections.Generic.IEqualityComparer<TKey> comparer
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HashMap(Int32)

Declaration
public HashMap(int initialCapacity)
Parameters
Type Name Description
System.Int32 initialCapacity
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HashMap(Int32, IEqualityComparer<TKey>)

Declaration
public HashMap(int initialCapacity, IEqualityComparer<TKey> comparer)
Parameters
Type Name Description
System.Int32 initialCapacity
System.Collections.Generic.IEqualityComparer<TKey> comparer

Properties

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Count

Declaration
public virtual int Count { get; }
Property Value
Type Description
System.Int32
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IsReadOnly

Declaration
public virtual bool IsReadOnly { get; }
Property Value
Type Description
System.Boolean
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Item[TKey]

Declaration
public virtual TValue this[TKey key] { get; set; }
Parameters
Type Name Description
TKey key
Property Value
Type Description
TValue
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Keys

Declaration
public virtual ICollection<TKey> Keys { get; }
Property Value
Type Description
System.Collections.Generic.ICollection<TKey>
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Values

Declaration
public virtual ICollection<TValue> Values { get; }
Property Value
Type Description
System.Collections.Generic.ICollection<TValue>

Methods

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Add(TKey, TValue)

Declaration
public virtual void Add(TKey key, TValue value)
Parameters
Type Name Description
TKey key
TValue value
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Add(KeyValuePair<TKey, TValue>)

Declaration
public virtual void Add(KeyValuePair<TKey, TValue> item)
Parameters
Type Name Description
System.Collections.Generic.KeyValuePair<TKey, TValue> item
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AddIfAbsent(TKey, TValue)

Declaration
public TValue AddIfAbsent(TKey key, TValue value)
Parameters
Type Name Description
TKey key
TValue value
Returns
Type Description
TValue
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Clear()

Declaration
public virtual void Clear()
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Contains(KeyValuePair<TKey, TValue>)

Declaration
public virtual bool Contains(KeyValuePair<TKey, TValue> item)
Parameters
Type Name Description
System.Collections.Generic.KeyValuePair<TKey, TValue> item
Returns
Type Description
System.Boolean
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ContainsKey(TKey)

Declaration
public virtual bool ContainsKey(TKey key)
Parameters
Type Name Description
TKey key
Returns
Type Description
System.Boolean
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ContainsValue(TValue)

Declaration
public bool ContainsValue(TValue value)
Parameters
Type Name Description
TValue value
Returns
Type Description
System.Boolean
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CopyTo(KeyValuePair<TKey, TValue>[], Int32)

Declaration
public virtual void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
Parameters
Type Name Description
System.Collections.Generic.KeyValuePair<TKey, TValue>[] array
System.Int32 arrayIndex
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Equals(Object)

Declaration
public override bool Equals(object obj)
Parameters
Type Name Description
System.Object obj
Returns
Type Description
System.Boolean
Overrides
System.Object.Equals(System.Object)
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GetEnumerator()

Declaration
public virtual IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
Returns
Type Description
System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<TKey, TValue>>
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GetHashCode()

Declaration
public override int GetHashCode()
Returns
Type Description
System.Int32
Overrides
System.Object.GetHashCode()
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Remove(TKey)

Declaration
public virtual bool Remove(TKey key)
Parameters
Type Name Description
TKey key
Returns
Type Description
System.Boolean
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Remove(KeyValuePair<TKey, TValue>)

Declaration
public virtual bool Remove(KeyValuePair<TKey, TValue> item)
Parameters
Type Name Description
System.Collections.Generic.KeyValuePair<TKey, TValue> item
Returns
Type Description
System.Boolean
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ToString()

Declaration
public override string ToString()
Returns
Type Description
System.String
Overrides
System.Object.ToString()
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TryGetValue(TKey, out TValue)

Declaration
public virtual bool TryGetValue(TKey key, out TValue value)
Parameters
Type Name Description
TKey key
TValue value
Returns
Type Description
System.Boolean

Explicit Interface Implementations

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IEnumerable.GetEnumerator()

Declaration
IEnumerator IEnumerable.GetEnumerator()
Returns
Type Description
System.Collections.IEnumerator

Implements

System.Collections.Generic.IDictionary<TKey, TValue>
System.Collections.Generic.ICollection<T>
System.Collections.Generic.IEnumerable<T>
System.Collections.IEnumerable

Extension Methods