How do I set a value in EditText if empty? [duplicate]

EditText edit = (EditText)findViewByid(R.id.edit); //estabeleço o conexão

if(edit.getText().toString().isEmpty()){ // verificando se a edit esta vazia

String num = "6"; // Ou use um int, não vejo necessidade de ser um double

edit.setText(num); //inserindo valor na edit
}

// code above works

// This is not below

// method calling by class public class Temperature {

public double getFaRetorneCels(double cel){
    return  ((cel*9)/5)+32;
}

public double getCelRetorneFa(double fah){
    return ((fah-32)*5/9);
}

}

// button code

public void convert (View view) {         EditText edtcel = (EditText) findViewById (R.id.edtCel);         EditText edtfa = (EditText) findViewById (R.id.ediFa);

    Temperatura t = new Temperatura();

     double c = Double.parseDouble(edtcel.getText().toString());
     double f = Double.parseDouble(edtfa.getText().toString());

    if(edtcel.getText().toString().isEmpty() && edtfa.getText().toString().isEmpty() ){
        Toast.makeText(this,"Pelo menos um campo deve ser preenchido!!!",Toast.LENGTH_SHORT).show();
    }else if(edtcel.getText().toString().isEmpty()) {

        edtcel.setText(String.valueOf(t.getCelRetorneFa(f)));

    }else  if (edtfa.toString().isEmpty()){

        edtfa.setText(String.valueOf(t.getFaRetorneCels(c)));


    }

If anyone can help thank you