Ex01, Calculator, Java file

package com.example.mybmicalculator16092022;

import androidx.appcompat.app.AppCompatActivity;

import android.graphics.Color;
import android.os.Bundle;


import android.view.View;
import android.widget.Button;

import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.RadioGroup;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    // 1 - define variables
    private EditText etNumber1;
    private EditText etNumber2;
    private TextView tvResult;

    private RadioGroup rgOperation;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // 0 - select a layout file for the activity
        setContentView(R.layout.activity_main);

        // 2 - bind each variable to a view from the layout
        etNumber1 = findViewById(R.id.etNo1);
        etNumber2 = findViewById(R.id.etNo2);
        tvResult = findViewById(R.id.tvResult);
        rgOperation = findViewById(R.id.rgOperation);
    }

    public void btnClicked(View view) {
        int n1, n2;
        // check user input data
        try {
            n1 = Integer.parseInt(etNumber1.getText().toString());
        } catch (Exception e) {
            tvResult.setText("Error: First number is missing or not integer");
            return;
        }
        try {
            String t = etNumber2.getText().toString();
            n2 = Integer.parseInt(t);
        } catch (Exception e) {
            tvResult.setText("Error: Second number is missing or not integer");
            return;
        }

        // check for selected operation
        double res = 0;
        String sign = "";

        int id = rgOperation.getCheckedRadioButtonId();
        // id=-1 if no operation was selected

        if (id == R.id.rbAdd) {
            res = n1 + n2;
            sign = "+";
        } else {
            if (id == R.id.rbSub) {
                res = n1 - n2;
                sign = "-";
            } else {
                if (id == R.id.rbMul) {
                    res = n1 * n2;
                    sign = "*";
                } else {
                    if (id == R.id.rbDiv) {
                        res = (double) n1 / n2;
                        sign = "/";
                        // error - res =(double) (n1 / n2);
                    } else {
                        tvResult.setText("You should Select an operation first");
                    }
                }
            }
        }

        // display result if no errors were found
        if (sign != "") {
            tvResult.setText(n1 + sign + n2 + " = " + res);
        }
    }
}