What you are trying to do is so, so trivial, I don't know how you could've searched any length of time at all and not have found dozens, if not hundreds, of examples. Anyway...
handler for the "Calculate Grade" button, call the
method for each
widget to get its value, and then call
to convert that value and assign it to each of your
variables. For example:
EditText et = (EditText) findViewById(R.id.grade1);
grade1 = Double.parseDouble(et.getText().toString());
Since it is read only, you should consider change the "Percentage"
to be a
widget instead. Then you can assign the sum to it like:
TextView tv = (TextView) findViewById(R.id.pct);
tv.setText(String.valueOf(grade1 + ...));