MainActivity.java

package com.ishtiaq.calculator;

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;

/*
* This is our Logic file (.java)
* */

//              this                    super
public class MainActivity extends AppCompatActivity {

    TextView tv1;
    EditText et1, et2;
    Button btn;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main); // আমরা View কে চিনিয়ে দিলাম
        // Start your own code from here

        tv1 = findViewById(R.id.myDisplay);
        et1 = findViewById(R.id.inputA);
        et2 = findViewById(R.id.inputB);
        btn = findViewById(R.id.myBtn);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                doMath();
            }
        });
    }

    void doMath()
    {
        int x = Integer.parseInt(et1.getText().toString());
        int y = Integer.parseInt(et2.getText().toString());
        int z = x + y;
        tv1.setText("Ans: " + z);
    }
}