C # Hash Table (Hashtable) Usage notes

First, what is Hashtable?

The Hashtable class represents a series of key/value pairs that are organized by key-based hash codes. It uses keys to access the elements in the collection.

When you use keys to access elements, a hash table is used, and you can identify a useful key value. Each item in the hash table has a key/value pair. Keys to access items in the collection

Second, the Hashtable property

1. Count gets the number of key-value pairs contained in the Hashtable.

2, Isfixedsize Gets a value that indicates whether the Hashtable has a fixed size.

3. IsReadOnly gets a value that indicates whether the Hashtable is read-only.

4. Item Gets or sets the value associated with the specified key.

5. Keys gets a ICollection that contains the keys in the Hashtable.

6. Values gets a ICollection that contains the values in the Hashtable.

Three, the method of Hashtable

Use in C # requires reference

Using System.Collections;

Using System.Collections.Generic;

These two namespaces

1. Public virtual void Add (object key, object value);

Purpose: Adds an element with the specified key and value to the Hashtable.

2, public virtual void Clear ();

Purpose: Removes all elements from the Hashtable.

3. Public virtual bool ContainsKey (object key);

Purpose: Determines whether the Hashtable contains the specified key.

4. Public virtual bool Containsvalue (object value);

Purpose: Determines whether the Hashtable contains the specified value.

5, public virtual void Remove (object key);

Purpose: Removes the element with the specified key from the Hashtable.

Iv. Application Scenarios for Hashtable

1, some data will be high frequency query

2, the amount of data is very large

3. Query field contains string type

4, data type is not unique

V. Examples of simple usages of Hashtable

Class Program

{

static void Main (string[] args)

{

Create a Hashtable instance

Hashtable ht=new Hashtable ();

Adding keyvalue key-value pairs

Ht. ADD ("A", "1");

Ht. ADD ("B", "2");

Ht. ADD ("C", "3");

Ht. ADD ("D", "4");

Traversing a hash table can only be traversed with foreach, because Hashtable cannot be accessed with an index

Traverse key

foreach (Object item in HT. Keys)

{

Console.WriteLine (string) item);

}

Traverse value

foreach (Object item in HT. Value)

{

Console.WriteLine (string) item);

}

foreach (DictionaryEntry de in HT)

{

Console.WriteLine ("Key--{0}; Value--{1}. ", De. Key, DE. Value);

}

Hash table Sort

ArrayList akeys=new ArrayList (ht. Keys);

Akeys. Sort ();

foreach (string skey in Akeys)

{

Console.WriteLine ("{0, -15} {1, -15}", Skey, Ht[skey]);

}

Determines whether the hash table contains a specific key with a return value of TRUE or False

if (HT. Contains ("A"))

Console.WriteLine (ht["A"]);

Assign a value to the corresponding key

ht["A"] = "Hello";

Remove a KeyValue key-value pair

Ht. Remove ("C");

Traversing a hash table

foreach (DictionaryEntry de in HT)

{

Console.WriteLine ("Key--{0}; Value--{1}. ", De. Key, DE. Value);

}

Remove all elements

Ht. Clear ();

There will be no output here

Console.WriteLine (ht["A"]);

Console.readkey ();

}

}

Public Number: Original

C # Hash Table (Hashtable) Usage notes