How to make a simple Demo Calculator

                                            Calculator

Xml Code:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
    tools:context=".MainActivity"
    tools:ignore="MissingClass">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="56dp"
        android:background="@drawable/border"
        android:padding="10dp"
        android:text="Demo Calculator"
        android:textColor="@color/black"
        android:textSize="30sp"
        android:textStyle="bold"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <EditText
        android:id="@+id/ed_2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="44dp"
        android:ems="10"
        android:inputType="number"
        app:layout_constraintEnd_toEndOf="@+id/ed_1"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="@+id/ed_1"
        app:layout_constraintTop_toBottomOf="@+id/ed_1" />

    <TextView
        android:id="@+id/txt_result"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="72dp"
        android:padding="5dp"
        android:text="Result"
        android:textColor="@android:color/holo_red_dark"
        android:textSize="20sp"
        app:layout_constraintEnd_toEndOf="@+id/btn_sum"
        app:layout_constraintHorizontal_bias="0.181"
        app:layout_constraintStart_toStartOf="@+id/btn_sum"
        app:layout_constraintTop_toBottomOf="@+id/btn_sum" />

    <Button
        android:id="@+id/btn_sum"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="24dp"
        android:text="Add"
        android:textSize="20sp"
        app:layout_constraintEnd_toEndOf="@+id/ed_2"
        app:layout_constraintHorizontal_bias="0.551"
        app:layout_constraintStart_toStartOf="@+id/ed_2"
        app:layout_constraintTop_toBottomOf="@+id/ed_2" />

    <EditText
        android:id="@+id/ed_1"
        android:layout_width="205dp"
        android:layout_height="62dp"
        android:layout_marginTop="32dp"
        android:ems="10"
        android:inputType="number"
        app:layout_constraintEnd_toEndOf="@+id/textView"
        app:layout_constraintHorizontal_bias="0.504"
        app:layout_constraintStart_toStartOf="@+id/textView"
        app:layout_constraintTop_toBottomOf="@+id/textView" />

    <Button
        android:id="@+id/btn_multi"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Multi"
        android:textSize="24sp"
        tools:ignore="MissingConstraints"
        tools:layout_editor_absoluteX="48dp"
        tools:layout_editor_absoluteY="323dp" />
</androidx.constraintlayout.widget.ConstraintLayout>

Java Code:

package com.example.uicon;

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 {

    private EditText ed_1 = findViewById(R.id.ed_1);
    private EditText ed_2 = findViewById(R.id.ed_2);
    private Button btn_sum = findViewById(R.id.btn_sum);
    private TextView txt_result = findViewById(R.id.txt_result);
    private Button btn_multi = findViewById(R.id.btn_multi);

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

        btn_sum.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                int num1=Integer.parseInt(ed_1.getText().toString());
                int num2=Integer.parseInt(ed_2.getText().toString());
                int sum=num1+num2;
                String Result=String.valueOf(sum);
                txt_result.setText(Result);
            }
        });
      btn_multi.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View view) {
              int num1=Integer.parseInt(ed_1.getText().toString());
              int num2=Integer.parseInt(ed_2.getText().toString());
              int multiply=num1*num2;
              txt_result.setText(multiply);
          }
      });


    }
}