MainActivity.java

package com.example.calculator;

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

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    Button buttonAdd, buttonSub, buttonMul, buttonDiv;
    EditText editTextN1, editTextN2;
    TextView textView;
    int num1, num2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EdgeToEdge.enable(this);
        setContentView(R.layout.activity_main);

        // UI references
        buttonAdd = findViewById(R.id.btn_add);
        buttonSub = findViewById(R.id.btn_sub);
        buttonMul = findViewById(R.id.btn_mul);
        buttonDiv = findViewById(R.id.btn_div);
        editTextN1 = findViewById(R.id.number1);
        editTextN2 = findViewById(R.id.number2);
        textView = findViewById(R.id.answer);

        // Set click listeners
        buttonAdd.setOnClickListener(this);
        buttonSub.setOnClickListener(this);
        buttonMul.setOnClickListener(this);
        buttonDiv.setOnClickListener(this);

        // Handle window insets
        ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {
            Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
            v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom);
            return insets;
        });
    }

    @Override
    public void onClick(View v) {
        String input1 = editTextN1.getText().toString().trim();
        String input2 = editTextN2.getText().toString().trim();

        if (input1.isEmpty() || input2.isEmpty()) {
            Toast.makeText(this, "Please enter both numbers", Toast.LENGTH_SHORT).show();
            return;
        }

        try {
            num1 = Integer.parseInt(input1);
            num2 = Integer.parseInt(input2);
        } catch (NumberFormatException e) {
            Toast.makeText(this, "Invalid number entered", Toast.LENGTH_SHORT).show();
            return;
        }

        if (v.getId() == R.id.btn_add) {
            textView.setText("Answer is: " + (num1 + num2));
        } else if (v.getId() == R.id.btn_sub) {
            textView.setText("Answer is: " + (num1 - num2));
        } else if (v.getId() == R.id.btn_mul) {
            textView.setText("Answer is: " + (num1 * num2));
        } else if (v.getId() == R.id.btn_div) {
            if (num2 != 0) {
                textView.setText("Answer is: " + (num1 / num2));
            } else {
                Toast.makeText(this, "Cannot divide by zero", Toast.LENGTH_SHORT).show();
                textView.setText("Error");
            }
        }
    }
}