title: check if array is just one letter
body: <p>I want to check if the input is only 1 letter or more than 1,
  below is my code</p>
  
  <pre><code>public ResponseEntity&lt;String&gt; moReceiver(@RequestParam("data")String data)
  String[]subKeyword=data.split(" ");
  String subKwd=subKeyword[1];
      if(subKwd =="")
      {
       System.out.println("One letter"); 
      }
      else
      {
       System.out.println("More than One letter"); 
      }
  </code></pre>
  
  <p>tried to use </p>
  
  <blockquote>
    <p>==""</p>
  </blockquote>
  
  <p>but doesnt work.. :( ,and got this error 
  --->Index 1 out of bounds for length 1</p>