void search() {
        System.out.println("Please enter search key");
        Scanner scan=new Scanner(System.in);
        String searchKey=scan.nextLine();
        String sRegExSearch = "\\b(?i:" + searchKey + ")\\b";
        Collection<String> collectionOfParagraphsContainingWord = mapOfWords.get(searchKey);
        for(String paragraph: collectionOfParagraphsContainingWord){
        String sModified = paragraph.replaceAll(sRegExSearch, "***$0***");

            System.out.println(sModified);
        }
    }
}