PARSEDOUBLE
  try {
     z1 = Double.parseDouble(tZahl.getText().toString());
  }
  catch (NumberFormatException e) {
     tOutput.setText("Fehlerhafte Zahl");
     return;
  }



    private Double getNumber(EditText edText) {
        try {
            String s= edText.getText().toString();
            double zahl = Double.parseDouble(s);
            return new Double(zahl);
        } catch (NumberFormatException e) {
            return Double.NaN;
        }
    }


parseInt
Random Zufallszahl