Caculator app in android, how to design calculator app

Main activity.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:clipToPadding="false"
    android:orientation="vertical"
    android:padding="10dp"
    app:barrierMargin="20dp"
    tools:context=".MainActivity">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="387dp"
        android:layout_height="159dp"
        app:srcCompat="@drawable/cal"
        android:contentDescription="TODO" />

    <EditText
        android:id="@+id/etFirstvalue"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="@string/enter_first_number"
        android:inputType="number"
        android:importantForAutofill="no" />

    <EditText
        android:id="@+id/etSecondvalue"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="@string/enter_second_number"
        android:inputType="number"
        android:autofillHints="" />

    <TextView
        android:id="@+id/tvAns"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:height="40dp" />

    <Button
        android:id="@+id/btnSum"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/plus"
        android:textStyle="bold" />

    <Button
        android:id="@+id/btnSubtract"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/minus"
        android:textStyle="bold" />

    <Button
        android:id="@+id/btnMultiply"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/multiply"
        android:textStyle="bold" />

    <Button
        android:id="@+id/btnDevision"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/devision"
        android:textStyle="bold" />

</LinearLayout>

Main Activity java code

package com.example.calculatorme;

import androidx.appcompat.app.AppCompatActivity;

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

public class MainActivity extends AppCompatActivity {
  EditText  etFirstvalue, etSecondvalue;
  TextView   tvAns;
  Button   btnSum,btnSubtract,btnMultiply,btnDevision;



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

        etFirstvalue= findViewById(R.id.etFirstvalue);
        etSecondvalue= findViewById(R.id.etSecondvalue);
        tvAns= findViewById(R.id.tvAns);
        btnSum= findViewById(R.id.btnSum);
        btnSubtract= findViewById(R.id.btnSubtract);
        btnMultiply= findViewById(R.id.btnMultiply);
        btnDevision= findViewById(R.id.btnDevision);

        btnSum.setOnClickListener(new View.OnClickListener() {
              @Override
            public void onClick(View v) {
            int  firstvalue, secondvalue, ans;
                  firstvalue= Integer.parseInt(etFirstvalue.getText().toString());
                  secondvalue= Integer.parseInt(etSecondvalue.getText().toString());
                  ans =  firstvalue +  secondvalue;
                  tvAns.setText("Ans is" + ans);
              }

        });

        btnSubtract.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int  firstvalue, secondvalue, ans;
                firstvalue= Integer.parseInt(etFirstvalue.getText().toString());
                secondvalue= Integer.parseInt(etSecondvalue.getText().toString());
                ans =  firstvalue -  secondvalue;
                tvAns.setText("Ans is" + ans);
            }

        });

        btnMultiply.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int  firstvalue, secondvalue, ans;
                firstvalue= Integer.parseInt(etFirstvalue.getText().toString());
                secondvalue= Integer.parseInt(etSecondvalue.getText().toString());
                ans =  firstvalue *  secondvalue;
                tvAns.setText("Ans is" + ans);
            }

        });

        btnDevision.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int  firstvalue, secondvalue, ans;
                firstvalue= Integer.parseInt(etFirstvalue.getText().toString());
                secondvalue= Integer.parseInt(etSecondvalue.getText().toString());
                ans =  firstvalue /  secondvalue;
                tvAns.setText("Ans is" + ans);
            }

        });


    }
}

Step 3: Paste a calculator icon in

drawable folder Android Development