title: Getting an error (java.lang.NullPointerException) on following code
body: <pre><code>import javax.swing.JOptionPane;
  
  public class SpeedOfSound {
      public static void main(String[] args) {
          String medium;
          double time = 0;
          double distance = 0;
  
          medium = JOptionPane.showInputDialog("Please enter a medium\n" + "(air, water, steel)");
          distance = Double.parseDouble(JOptionPane.showInputDialog("Please enter the distance the soundwave has to travel"));
  
          if (medium.equalsIgnoreCase("air")) {
              time = distance / 1100;
          } else if (medium.equalsIgnoreCase("water")) {
              time = distance / 4900;
          } else if (medium.equalsIgnoreCase("steel")) {
              time = distance / 16400;
          }
  
          System.out.println(time);
          System.exit(0);
      }
  }
  </code></pre>
  
  <p>I've never encountered this error and I can't point out what it even is given the code. Any help would be appreciated. Thanks.</p>
  
  <p>Edit: someone mentioned that the question is a duplicate. I looked at that question before posting this. Again, I don't understand the context of my error. The previous question says the exception happens when the pointer points to "null" I can't seem to find an instance where I don't have anything pointing to the respective values.</p>