Alert dialog for no internet connection in android studio

in main activity java file -->

ConnectivityManager connectivityManager= (ConnectivityManager) getApplicationContext().getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo =connectivityManager.getActiveNetworkInfo();
if (networkInfo == null || !networkInfo.isConnected() || !networkInfo.isAvailable()){
    Dialog dialog=new Dialog(this);
    dialog.setContentView(R.layout.alert_dialog);
    dialog.setCancelable(false);
    dialog.getWindow().setLayout(WindowManager.LayoutParams.WRAP_CONTENT,WindowManager.LayoutParams.WRAP_CONTENT);
    dialog.getWindow().getAttributes().windowAnimations =android.R.style.Animation_Dialog;

    Button button=dialog.findViewById(R.id.alertbtn);
    button.setOnClickListener(new View.OnClickListener() {
        @Override        public void onClick(View view) {
            recreate();
        }
    });
    dialog.show();
}

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in layout resource file

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:gravity="center"    android:orientation="vertical"    android:layout_margin="10dp">
    <ImageView        android:layout_width="160dp"        android:layout_height="200dp" />
    <TextView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="No Internet!"        android:textSize="25sp"/>

    <TextView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="Please check internet connection!!"        android:textSize="16sp"        android:textColor="#000000"/>
    <Button        android:id="@+id/alertbtn"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:background="#03a9f4"        android:layout_margin="40dp"        android:text="Retry"/>


</LinearLayout>