MainActivity

package com.example.calcapp2;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {
    public EditText p1, p2;
    public Button b_add, b_minus, b_mul, b_del;
    public TextView textView;
    int a, b;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        p1 = findViewById(R.id.arg1);
        p2 = findViewById(R.id.arg2);
        b_add = findViewById(R.id.add);
        b_minus = findViewById(R.id.subtr);
        b_mul = findViewById(R.id.mul);
        b_del = findViewById(R.id.divide);
        textView = findViewById(R.id.answer);
    }

    public boolean init() {
        boolean ans = true;
        try {
            a = Integer.parseInt(p1.getText().toString());
        } catch (NumberFormatException e) {
            ans = false;
        }
        try {
            b = Integer.parseInt(p2.getText().toString());
        } catch (NumberFormatException r) {
            ans = false;
        }
        if (!ans) {
            textView.setText("Input Error");
        }
        return ans;
    }

    public void onClickAdd(View view) {
        boolean f = init();
        if (f) {
            textView.setText(Integer.toString((a + b)));
        }
    }

    public void onClickMinus(View view) {
        boolean f = init();
        if (f) {
            textView.setText(Integer.toString((a - b)));
        }
    }

    public void onClickMul(View view) {
        boolean f = init();
        if (f) {
            textView.setText(Integer.toString((a * b)));
        }
    }

    public void onClickDel(View view) {
        boolean f = init();
        if (f) {
            if (b != 0) {
                textView.setText(Integer.toString((a / b)));
            } else {
                textView.setText("Div by zero");
            }
        }
    }
}