Csharp/CSharp Tutorial/Data Structure/Hashtable

Add elements to the table and Use the keys to obtain the values

using System; 
using System.Collections; 
 
class HashtableDemo { 
  public static void Main() { 
    Hashtable ht = new Hashtable(); 
     
    
    ht.Add("a", "A"); 
    ht.Add("b", "B"); 
    ht.Add("c", "C"); 
    ht.Add("e", "E"); 
 
    // Get a collection of the keys. 
    ICollection c = ht.Keys; 
 
    foreach(string str in c) 
      Console.WriteLine(str + ": " + ht[str]); 
  } 
}

a: A
b: B
c: C
e: E

Add key-value pair to Hashtable by using the indexer

using System; 
using System.Collections; 
 
class HashtableDemo { 
  public static void Main() { 
    Hashtable ht = new Hashtable(); 
     
    
    ht.Add("a", "A"); 
    ht.Add("b", "B"); 
    ht.Add("c", "C"); 
    ht.Add("e", "E"); 
    
    ht["f"] = "F"; 
 
    // Get a collection of the keys. 
    ICollection c = ht.Keys; 
 
    foreach(string str in c) 
      Console.WriteLine(str + ": " + ht[str]); 
  } 
}

a: A
b: B
c: C
e: E
f: F

Clear all key/value pairs in a Hashtable

using System;
using System.Collections;
class MainClass
{
  static void Main(string[] args)
  {
    Hashtable a = new Hashtable(10);
          
    a.Add(100, "Arrays");
    a.Add(200, "Classes");
    
    a.Clear();
  }
}

Copy the keys from Hashtable into an array using the CopyTo() method and then display the array contents

using System;
using System.Collections;
class MainClass
{
  public static void Main()
  {
    Hashtable myHashtable = new Hashtable();
    myHashtable.Add("AL", "Alabama");
    myHashtable.Add("CA", "California");
    myHashtable.Add("FL", "Florida");
    myHashtable.Add("NY", "New York");
    myHashtable.Add("WY", "Wyoming");
    foreach (string myKey in myHashtable.Keys)
    {
      Console.WriteLine("myKey = " + myKey);
    }
    foreach(string myValue in myHashtable.Values)
    {
      Console.WriteLine("myValue = " + myValue);
    }
    
    Console.WriteLine("Copying keys to myKeys array");
    string[] myKeys = new string[5];
    myHashtable.Keys.CopyTo(myKeys, 0);
    
    for (int counter = 0; counter < myKeys.Length; counter++) {
      Console.WriteLine("myKeys[" + counter + "] = " + myKeys[counter]);
    }
  }
}

myKey = NY
myKey = CA
myKey = FL
myKey = WY
myKey = AL
myValue = New York
myValue = California
myValue = Florida
myValue = Wyoming
myValue = Alabama
Copying keys to myKeys array
myKeys[0] = NY
myKeys[1] = CA
myKeys[2] = FL
myKeys[3] = WY
myKeys[4] = AL

Copy the values from Hashtable into an array using the CopyTo() method and then display the array contents

using System;
using System.Collections;
class MainClass
{
  public static void Main()
  {
    Hashtable myHashtable = new Hashtable();
    myHashtable.Add("AL", "Alabama");
    myHashtable.Add("CA", "California");
    myHashtable.Add("FL", "Florida");
    myHashtable.Add("NY", "New York");
    myHashtable.Add("WY", "Wyoming");
    foreach (string myKey in myHashtable.Keys)
    {
      Console.WriteLine("myKey = " + myKey);
    }
    foreach(string myValue in myHashtable.Values)
    {
      Console.WriteLine("myValue = " + myValue);
    }
    
    Console.WriteLine("Copying values to myValues array");
    string[] myValues = new string[5];
    myHashtable.Values.CopyTo(myValues, 0);
    for (int counter = 0; counter < myValues.Length; counter++)
    {
      Console.WriteLine("myValues[" + counter + "] = " + myValues[counter]);
    }
  }
}

myKey = NY
myKey = CA
myKey = FL
myKey = WY
myKey = AL
myValue = New York
myValue = California
myValue = Florida
myValue = Wyoming
myValue = Alabama
Copying values to myValues array
myValues[0] = New York
myValues[1] = California
myValues[2] = Florida
myValues[3] = Wyoming
myValues[4] = Alabama

Mark a Hashtable to be Synchronized

using System;
using System.Collections;
class MainClass
{
  static void Main(string[] args)
  {
    Hashtable a = new Hashtable(10);
    Hashtable.Synchronized(a);
          
  }
}

Remove key/value pairs from Hashtable

using System;
using System.Collections;
class MainClass
{
  static void Main(string[] args)
  {
    Hashtable a = new Hashtable(10);
          
    a.Add(100, "A");
    a.Add(200, "C");
    
    a.Remove(100);
    a.Remove(200);
  }
}

Use foreach statement to loop through all keys in a hashtable

using System;
using System.Collections;
class MainClass
{
    public static void Main()
    {
        Hashtable    hash = new Hashtable();
        hash.Add("A", "1");
        hash.Add("B", "2");
        hash.Add("C", "3");
        hash.Add("D", "4");
        hash.Add("E", "5");
        
        foreach (string firstName in hash.Keys)
        {
            Console.WriteLine("{0} {1}", firstName, hash[firstName]);
        }
    }
}

A 1
B 2
C 3
D 4
E 5

Use the ContainsKey() method to check if Hashtable contains a key

using System;
using System.Collections;
class MainClass
{
  public static void Main()
  {
    Hashtable myHashtable = new Hashtable();
    myHashtable.Add("AL", "Alabama");
    myHashtable.Add("CA", "California");
    myHashtable.Add("FL", "Florida");
    myHashtable.Add("NY", "New York");
    myHashtable.Add("WY", "Wyoming");
    foreach (string myKey in myHashtable.Keys)
    {
      Console.WriteLine("myKey = " + myKey);
    }
    foreach(string myValue in myHashtable.Values)
    {
      Console.WriteLine("myValue = " + myValue);
    }
    
    if (myHashtable.ContainsKey("FL"))
    {
      Console.WriteLine("myHashtable contains the key FL");
    }
  }
}

myKey = NY
myKey = CA
myKey = FL
myKey = WY
myKey = AL
myValue = New York
myValue = California
myValue = Florida
myValue = Wyoming
myValue = Alabama
myHashtable contains the key FL

Use the ContainsValue() method to check if Hashtable contains a value

using System;
using System.Collections;
class MainClass
{
  public static void Main()
  {
    Hashtable myHashtable = new Hashtable();
    myHashtable.Add("AL", "Alabama");
    myHashtable.Add("CA", "California");
    myHashtable.Add("FL", "Florida");
    myHashtable.Add("NY", "New York");
    myHashtable.Add("WY", "Wyoming");
    foreach (string myKey in myHashtable.Keys)
    {
      Console.WriteLine("myKey = " + myKey);
    }
    foreach(string myValue in myHashtable.Values)
    {
      Console.WriteLine("myValue = " + myValue);
    }
    
    if (myHashtable.ContainsValue("Florida"))
    {
      Console.WriteLine("myHashtable contains the value Florida");
    }
  }
}

myKey = NY
myKey = CA
myKey = FL
myKey = WY
myKey = AL
myValue = New York
myValue = California
myValue = Florida
myValue = Wyoming
myValue = Alabama
myHashtable contains the value Florida

Use the Remove() method to remove FL from Hashtable

using System;
using System.Collections;
class MainClass
{
  public static void Main()
  {
    Hashtable myHashtable = new Hashtable();
    myHashtable.Add("AL", "Alabama");
    myHashtable.Add("CA", "California");
    myHashtable.Add("FL", "Florida");
    myHashtable.Add("NY", "New York");
    myHashtable.Add("WY", "Wyoming");
    foreach (string myKey in myHashtable.Keys)
    {
      Console.WriteLine("myKey = " + myKey);
    }
    foreach(string myValue in myHashtable.Values)
    {
      Console.WriteLine("myValue = " + myValue);
    }
    
    Console.WriteLine("Removing FL from myHashtable");
    myHashtable.Remove("FL");
  }
}

myKey = NY
myKey = CA
myKey = FL
myKey = WY
myKey = AL
myValue = New York
myValue = California
myValue = Florida
myValue = Wyoming
myValue = Alabama
Removing FL from myHashtable