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"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="This is an activity"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.java

package com.learnoset.nointernetdialog;

import android.content.Context;
import android.graphics.drawable.ColorDrawable;
import android.net.ConnectivityManager;
import android.os.Bundle;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

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

        // check if network is connected
        if (!checkInternet()) {

            // show no internet dialog
            NoInternetDialog noInternetDialog = new NoInternetDialog(MainActivity.this);
            noInternetDialog.setCancelable(false);
            noInternetDialog.getWindow().setBackgroundDrawable(new ColorDrawable(getResources().getColor(android.R.color.transparent)));
            noInternetDialog.show();
        }

    }

    private boolean checkInternet() {
        ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        return connectivityManager.getActiveNetworkInfo() != null && connectivityManager.getActiveNetworkInfo().isConnected();
    }
}

no_internet_dialog_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.cardview.widget.CardView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="80dp"
        android:layout_marginBottom="80dp"
        app:cardBackgroundColor="#90C9DB"
        app:cardCornerRadius="10dp"
        app:cardUseCompatPadding="true">

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_above="@+id/shapeDivider"
                android:layout_marginStart="20dp"
                android:layout_marginBottom="120dp"
                android:layout_toStartOf="@+id/birdIcon"
                android:gravity="center">

                <ImageView
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:adjustViewBounds="true"
                    android:src="@drawable/cloud_icon_01" />
            </LinearLayout>

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_above="@+id/lineIcon"
                android:layout_alignParentEnd="true"
                android:layout_toEndOf="@id/birdIcon"
                android:gravity="center">

                <ImageView
                    android:layout_width="50dp"
                    android:layout_height="wrap_content"
                    android:adjustViewBounds="true"
                    android:src="@drawable/cloud_icon_02" />
            </LinearLayout>

            <ImageView
                android:layout_width="80dp"
                android:layout_height="wrap_content"
                android:layout_above="@+id/lineIcon"
                android:layout_marginEnd="-30dp"
                android:layout_marginBottom="-20dp"
                android:layout_toStartOf="@+id/birdIcon"
                android:adjustViewBounds="true"
                android:src="@drawable/cloud_icon_03" />

            <ImageView
                android:id="@+id/lineIcon"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_above="@+id/shapeDivider"
                android:layout_marginStart="-100dp"
                android:layout_marginEnd="-100dp"
                android:layout_marginBottom="80dp"
                android:adjustViewBounds="true"
                android:src="@drawable/line_icon" />

            <ImageView
                android:id="@+id/birdIcon"
                android:layout_width="100dp"
                android:layout_height="wrap_content"
                android:layout_above="@+id/shapeDivider"
                android:layout_centerHorizontal="true"
                android:layout_marginBottom="80dp"
                android:adjustViewBounds="true"
                android:src="@drawable/bird_icon" />

            <ImageView
                android:id="@+id/shapeDivider"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_centerInParent="true"
                android:adjustViewBounds="true"
                android:src="@drawable/shape" />

            <RelativeLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_below="@+id/shapeDivider"
                android:background="#FFFFFF">

                <TextView
                    android:id="@+id/noInternetTitle"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_marginTop="20dp"
                    android:fontFamily="@font/hammersmith_one"
                    android:gravity="center"
                    android:text="No Internet Connection"
                    android:textColor="#000000"
                    android:textSize="22sp"
                    android:textStyle="bold" />

                <TextView
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_above="@+id/retryBtn"
                    android:layout_below="@+id/noInternetTitle"
                    android:layout_marginStart="20dp"
                    android:layout_marginEnd="20dp"
                    android:gravity="center"
                    android:lineSpacingExtra="8dp"
                    android:text="You are not connected to the internet.\nMake sure wifi is on, internet is on, Airplane mode is off and try again."
                    android:textSize="16sp" />


                <androidx.appcompat.widget.AppCompatButton
                    android:id="@+id/retryBtn"
                    android:layout_width="wrap_content"
                    android:layout_height="45dp"
                    android:layout_alignParentBottom="true"
                    android:layout_centerHorizontal="true"
                    android:layout_marginBottom="30dp"
                    android:background="@drawable/round_back_stroke"
                    android:paddingStart="80dp"
                    android:paddingEnd="80dp"
                    android:text="Retry"
                    android:textColor="#324460" />
            </RelativeLayout>
        </RelativeLayout>
    </androidx.cardview.widget.CardView>
</RelativeLayout>

NoInternetDialog.java

package com.learnoset.nointernetdialog;

import android.app.Dialog;
import android.content.Context;
import android.os.Bundle;
import android.view.View;

import androidx.annotation.NonNull;
import androidx.appcompat.widget.AppCompatButton;

public class NoInternetDialog extends Dialog {
    public NoInternetDialog(@NonNull Context context) {
        super(context);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.no_internet_dialog_layout);

        final AppCompatButton retryBtn = findViewById(R.id.retryBtn);

        retryBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                // your code here...

                dismiss();
            }
        });
    }
}