Shortest Code for a Simple Calculator on Android

String RESULT;
String input = "(1+3)/4 * 2 - 7";
...
webSettings.setJavaScriptEnabled(true);
...
webView.addJavascriptInterface(new JavaScriptInterface() {
   public void returnResult(String o) {
       RESULT = o;
   }}, "JavaCallback"));
webView.loadUrl("javascript:window.JavaCallback"
   + ".returnResult("+input+")");
// now RESULT is -5

Is there a shorter one? BTW: this is only a sketch not sure if I've missed a bracket somewhere …

From http://karussell.wordpress.com/2011/12/09/shortest-code-for-a-simple-calculator-on-android/