The resulting app consists of 4 components,
a edit text field, a radio button group containing 6 radio
buttons, a text view and a button.
The user could first input human age in the edit text field,
then select one of 6 radio buttons to indicate the target animal age,
and finally click the convert button, the resulting animal age will be shown
in the text view. If the user doesn’t input a valid number of human age or
doesn’t select a radio button, the app will show the approriate warning messag