Q:

Android - Program crashes when there is not input in editText fields

So i'm having a problem in my code which is probably simple to solve but its my first app so cut me some slack. When I enter no values in my editText box my app crashes. Im semi aware why it occurs but I cant seem to solve it. 
public void onButtonClick( View v)
    {
        Double n1  , n2 , answer1;
        EditText e1 = (EditText) findViewById(R.id.num1);
        EditText e2 = (EditText) findViewById(R.id.num2);
        TextView t1 = (TextView) findViewById(R.id.answer);
        n1 = Double.parseDouble(e1.getText().toString());
        n2 = Double.parseDouble(e2.getText().toString());
        if (n1.toString().length()< 0 || n2.toString().length()< 0){
            t1.setText("Please enter a number into both the base and height");
        }else {
            answer1 = ((n1 * n2) / 2);
            t1.setText(Double.toString(answer1));
        }
    }

A:

First check if there is input in both EditTexts and only if there is convert it to Double:
if (e1.getText().length() == 0 || e2.getText().length() == 0) {
    t1.setText("Please enter a number into both the base and height");
} else {
    n1 = Double.parseDouble(e1.getText().toString());
    n2 = Double.parseDouble(e2.getText().toString());
    answer1 = ((n1 * n2) / 2);
    t1.setText(Double.toString(answer1));
}

EditText.getText() will never return null (as per source code) so it's safe to use methods on it (such as length().

