Catching And Stopping One Decimal Point Error

Alright how does one catch and stop a one decimal point error? The user inputs a single . and that is all; you can not allow that because you will be doing math with that input.if you have this in your xml file:

Code:
<EditText
android:id="@+id/edittext01"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:inputType="number|numberDecimal"
android:lines="1" >
</EditText>

and the user types just one decimal and nothing else the program will blow up.I tried the following code but the program blows up at the second IF.At first the two IFs were just one line, they got broken up to see where the problem was As you can see if the length of the user input is only 1 we check to see if it is only one decimal only

The program blows up at the second IF, but errx is a STRING.I used the Log.i to see how far to program went. And the errx is a "."

Code:
if (stop == 0) // checking for one decimal only and nothing else
{
String errx =null;
errx = (edtxt01.getText().toString());
Log.i("ONE DEC:", "START OF IF xxxx: " + errx);
if (edtxt01.length() == 1 ) // *********** 1st if
[code]...