How to programmatically set image to ImageView in Android

activity_main.xml

<?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"
    android:padding="24dp"
    tools:context=".MainActivity"
    android:background="#DCDCDC">

    <ImageView
        android:id="@+id/iv"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.java

package com.cfsuman.androidtutorials;

import android.app.Activity;
import android.os.Bundle;
import android.widget.ImageView;


public class MainActivity extends Activity {
        private ImageView mImageView;

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

                // Get the widgets reference from XML layout
                mImageView = (ImageView) findViewById(R.id.iv);

                /*
                    public void setImageResource (int resId)
                        Sets a drawable as the content of this ImageView.

                        Related XML Attributes
                            android:src

                        Parameters
                            resId : the resource identifier of the drawable
                 */

                // Set the ImageView image programmatically
                mImageView.setImageResource(R.drawable.flower5);
        }
}