title: The operator * is undefined for the argument type(s) double, EditText
body: <p>I'm really not sure why I get this error. It's probably something simple but I'm new to this.</p>
  
  <pre><code>final Button calculate = (Button) findViewById(R.id.calculate);
  calculate.setOnClickListener(new View.OnClickListener() {
          // Implement the OnClickListener callback       
          private void onClick(Button calculate) {
                  double perimeter = 2 * (Math.PI * entry); //error on this line
                  System.out.print(perimeter);
  
                  }
  
          public void onClick(View v) {
          // TODO Auto-generated method stub
              }
          }
  
      );
  </code></pre>