Question

How does one code for a choice between two options?

if ((one_spinner.getSelectedItem().toString()
                    .equals("one"))) {
                double one_thing = new Double(one.getText()
                        .toString());
                double two_thing = one_thing * 5;

            } else {
                double two_thing = new Double(one.getText()
                        .toString());
                double one_thing = two / 5;
            }

Answer 1

Assuming you want to refer to one_thing and two_thing after the if statement, you need to declare them before the if statement, so that they’ll still be in scope:

double one_thing;
double two_thing;
if (one_spinner.getSelectedItem().toString().equals("one")) {
   one_thing = Double.parseDouble(one.getText().toString());
   two_thing = one_thing * 5;
} else {
   two_thing = Double.parseDouble(one.getText().toString());
   one_thing = two_thing / 5;
}

Note that this can be simplified in terms of removing redundant code:

double parsedValue = Double.parseDouble(one.getText().toString());

double one_thing;
double two_thing;
if (one_spinner.getSelectedItem().toString().equals("one")) {
   one_thing = parsedValue;
   two_thing = one_thing * 5;
} else {
   two_thing = parsedValue;
   one_thing = two_thing / 5;
}

Or, given that the relationship between the two is always a factor of 5:

double one_thing = Double.parseDouble(one.getText().toString());
if (one_spinner.getSelectedItem().toString().equals("one")) {
   one_thing = one_thing / 5;
}
double two_thing = one_thing * 5;

Note that conventionally these names would be oneThing and twoThing, by the way.