HashTable in C#

using System;
using System.Collections;

public class SimpleHashing
{
   private static readonly int BUCKETS_DEFAULT = 16;

   private HashNode[] buckets;
   private int numBuckets;
   public int Size { get; private set; }

   public class HashNode
   {
       public string key;
       public string value;
       public HashNode next;

       public HashNode(string key, string value)
       {
           this.key = key;
           this.value = value;
           this.next = null;
       }
       public HashNode(string key, string value, HashNode next)
       {
           this.key = key;
           this.value = value;
           this.next = next;
       }
   }

   public SimpleHashing()
   {
       this.numBuckets = BUCKETS_DEFAULT;
       buckets = new HashNode[numBuckets];
   }

   public  SimpleHashing(int numBuckets)
   {
       this.numBuckets = numBuckets;
       buckets = new HashNode[numBuckets];
   }

   public bool IsEmpty()
   {
       return Size <= 0;
   }

   private int GetHash(string key)
   {
       return (key.GetHashCode() & 0x7fffffff) % numBuckets;
   }

   public void Put(string key, string value)
   {
       int bucket = GetHash(key);
       HashNode newNode = new HashNode(key, value);
       if(buckets[bucket] == null)
       {
           buckets[bucket] = newNode;
           Size++;
       }
       else
       {
           HashNode tmp = buckets[bucket];
           while(tmp.next != null)
           {
               if (tmp.key.Equals(key))
               {
                   tmp.value = value;
                   return;
               }
               tmp = tmp.next;
           }
           tmp.next = newNode;
           Size++;
       }
       return;
   }

   public string Get(string key)
   {
       int bucket = GetHash(key);
       HashNode tmp = buckets[bucket];
       while(tmp != null)
       {
           if (tmp.key.Equals(key))
           {
               return tmp.value;
           }
       }
       return null;
   }

   public void Remove(string key)
   {
       int bucket = GetHash(key);
       if(buckets[bucket] == null)
       {
           return;
       }
       HashNode tmp = buckets[bucket];
       if (tmp.key.Equals(key))
       {
           buckets[bucket] = buckets[bucket].next;
           Size--;
           return;
       }
       while(tmp.next != null)
       {
           if (tmp.next.key.Equals(key))
           {
               tmp.next = tmp.next.next;
               Size--;
               return;
           }
           tmp = tmp.next;
       }
   }

   public void Clear()
   {
       buckets = new HashNode[numBuckets];
   }

   override
       public string ToString()
   {
       string res = "{";
       int count = 0;
       for(int i = 0; i < numBuckets; i++)
       {
           if(buckets[i] != null)
           {
               HashNode tmp = buckets[i];
               while(tmp != null)
               {
                   res += tmp.key + ": " + tmp.value;
                   count++;
                   if(count < Size)
                   {
                       res += ", ";
                   }
                   tmp = tmp.next;
               }
           }
       }
       res += "}";
       return res;
   }
}