Double.parseDouble behavior

this is something I don't get...

I declared like this:
minXSinTField = new JTextField("0.0", 4);

and then I am using this func to test input validation.
isValidInput(minXSinTField);

This is the func.
  public boolean isValidInput(JTextField tf) {
    boolean result = true;
    try {
      Double.parseDouble(tf.getText());
      result = true;
      System.out.println("in try section");
      System.out.println(result);
    }
    catch (NumberFormatException ex) {
      result = false;
      System.out.println("in  catch section");
      System.out.println(result);
    }
    System.out.println("before return;");
    System.out.println(result);
    return result;
  }

Now, when I enter any string this func returns true.
From other pane's textfields, when I enter string this func returns false.

I don't know why...