Use of a hash table (hashtable) with Instances

Hashtable is usually called a hash table, which represents a set of key/value pairs.

1. hashtable constructor:

Hashtable () // empty instance initialized to 0 Elements
Hashtable (int32) // a new instance initialized to int32 Elements

Example:
Hashtable myhashtable1 = new hashtable ();
Hashtable myhashtable2 = new hashtable (5 );

2. Features of The hashtable Element

The hashtable method to obtain elements is to use"Key"Value corresponding to the access key, that is, hashtable [Key]. The following is an example:

Using system;
Using system. Collections. Generic;
Using system. text;
Using system. collections;

Namespace example9_22
{
Class Program
{
Static void main (string [] ARGs)
{
Hashtable myhashtable = new hashtable ();
// Insert the corresponding key and Value Elements
Myhashtable. Add (1, "H ");
Myhashtable. Add (2, "e ");
Myhashtable. Add (3, "L ");
Myhashtable. Add (4, "L ");
Myhashtable. Add (5, "O ");
Myhashtable. Add ("int", 1 );
Myhashtable. Add ("double", 2.3 );
Myhashtable. Add ("bool", true );
// Modify the elements composed of keys and values
Myhashtable ["int"] = 23;
Myhashtable ["double"] = 1.5;
Myhashtable ["bool"] = false;
// Outputs the elements composed of the corresponding keys and values.
Console. writeline (myhashtable [1]);
Console. writeline (myhashtable [2]);
Console. writeline (myhashtable [3]);
Console. writeline (myhashtable [4]);
Console. writeline (myhashtable [5]);
Console. writeline (myhashtable ["int"]);
Console. writeline (myhashtable ["double"]);
Console. writeline (myhashtable ["bool"]);
Console. Readline ();
}
}
}
Program The running result is as follows:
H
E
L
L
O
23
1.5
False

3. operations on the hashtable Element

● The add operation is defined as follows:
Public Virtual void add (Object key, lbject value)

Note: The "key" cannot be blank, and the "value can be blank ".

● Delete operation:
Hashtable. Clear () // delete all elements without any parameters. After clearing, the number of hashtable elements is 0.
Example: myhashtable. Clear ()
Hashtable. Remove () // Delete the element where the specified "key" is located.
It is defined as follows:
Public Virtual void remove (Object key)
Example: myhashtable. Remove ("int ");

If hashtable is read-only, the above operation will be abnormal..

4. hashtable Traversal

Because the hashtable key-Value Pair belongs to the dictionaryentry type, when we use foreach to traverse hashtable, the type parameter is: dictionaryentry. See the following example:
Foreach (dictionatyentry, myde in myhashtable)
{
Console. writeline ("\ t {0} \ t {1 }",Myde. Key, myde. Value);//Note the key-value reading method.
}

5. query hashtable

You can use the following methods to query hashtable:
● Hashtable. Contains // determines whether hashtable contains the specified "key ".
● Hashtable. containskey // checks whether hashtable contains the specified "key ". Same as above
● Hashtable. containsvalue // determines whether or not hashtable contains the specified value. Good!

Example:
Console. writeline ("myhashtable contains key 1: {0}", myhashtable. Contains (1 ));
Console. writeline ("myhashtable contains key 6: {0}", myhashtable. containskey (6 ));
Console. writeline ("myhashtable include value true: {0}", myhashtable. containsvalue (true ));
Console. writeline ("myhashtable contains value 3.3: {0}", myhashtable. containsvalue (2.2 ));

6. Advantages of hashtable tables

hashtable is system. A container provided by the collections namespace. The key/value in hashtable is of the object type, hashtable supports key/value pairs of any type .
the advantage of hashtable lies in its indexing method. the indexing speed is very fast .