title: The method join (String, List<String>) is undefined for the type String
body: <p>I'm learning Java and I have come across one tutorial about Hash Maps and start typing the same code like my tutor. The problem is when I came across String.join method, I got an error and my tutor didn't, and I do not know why.</p>
  
  <p>This is the error:</p>
  
  <pre><code>The method join(String, List&lt;String&gt;) is undefined for the 
  type String
  </code></pre>
  
  <p>Can you tell me whats the problem?</p>
  
  <pre><code>private String getZnanjaList(){
  
      List &lt;String&gt; listaZnanja = new ArrayList&lt;&gt;();
  
      for (String znanje : this.znanja.keySet()){
          listaZnanja.add(znanje + ": " + this.znanja.get(znanje));
      }
  
      return String.join("; ", listaZnanja);
  }
  </code></pre>