title: Hash table / insert a new key & value
body: <p>As I understand, there is a option in java to insert a new key to HashTable.
  This done by:</p>
  
  <pre><code> Hashtable&lt;String,String&gt; hashTable=new Hashtable&lt;String,String&gt;();
   hashTable.put("Donald", "Trump");
  </code></pre>
  
  <p>Where donald is the key, and Trump is the value. If I want to add the value "TrumpY" to "Donald", than I use the same operation:</p>
  
  <pre><code> hashTable.put("Donald", "TrumpY");
  </code></pre>
  
  <p>I have a question about the time complexity of this operation. As I understand the time complexity  is <code>O(1)</code>. But this is relavant for the first and the second operation? because the first need to add a new key to the hash table, and the second need to add only a value to key that already exists.</p>