title: Added java debugging which is not causing my java program to throw errors
body: <p>I have the following simple Java program:</p>
  <pre><code>public static void main(String[] args) 
  { 
      Scanner input = new Scanner(System.in); 
      
      double rad;  
      double area;  
   
      System.out.print(&quot;radius #: &quot;); 
      rad = input.nextDouble(); 
      System.err.println(rad);
  
      area = rad * rad * 3.14159; 
   
      System.out.println(&quot;Radius &quot;  
       + rad + &quot; is &quot; + area); 
  
       input.close();
   } 
  }
  </code></pre>
  <p>It was running great, but I wanted to practice debugging, so I added this line:</p>
  <pre><code>System.err.println(rad);
  </code></pre>
  <p>And it now gives me this error:</p>
  <pre><code>Exception in thread &quot;main&quot; java.util.InputMismatchException
          at java.base/java.util.Scanner.throwFor(Scanner.java:939)
          at java.base/java.util.Scanner.next(Scanner.java:1594)
          at java.base/java.util.Scanner.nextDouble(Scanner.java:2564)
          at ComputeArea.main(ComputeArea.java:20)
  </code></pre>
  <p>What could I be doing wrong?</p>
  <p>thanks!</p>