Suppose that we are working for an online service that provides a bulletin board for its users. We would like to give our users the option of filtering out profanity. Suppose that we consider the words cat, dog, and llama to be profane. Write a program that reads a string from the keyboard and tests whether the string contains one of our profane words. Your program should find words like cAt that differ only in case. Option: As an extra challenge, have your program reject only lines that contain a profane word exactly. For example, Dogmatic concatenation is a small category should not be considered profane.

Here is the JAVA program:

import java.util.*;   //to use Scanner class, Lists

public class Main{  //name of class

public static void main(String[] args) {  //start of main function

   String sentence = "CaT and catalog are not same";  //a string

   sentence = sentence.toLowerCase();  // converts the words in the sentence to lowercase

   Scanner sc = new Scanner(sentence);  //creates Scanner class object

   List<String> profane_words = profaneList();  // creates a list of profane words i.e. cat, dog and llama

   int count = 0;  //count the number of profane words

   while (sc.hasNext()) {  //reads string as tokens and returns true if scanner has another token

       String word = sc.next();  //returns the next complete token (word) and store it into word variable

       for (String profane : profane_words) {  // looks for each profane in profane_words list

           if (word.matches(".*\\b" + profane + "\\b.*") && ! sentence.matches(".*" + profane + "[a-z].*\\b" + profane + "\\b.*") && ! sentence.matches(".*[a-z]" + profane + ".*\\b" + profane + "\\b.*")) {  //uses matches() method that identifies whether a word in the string matches the given regular expression.

               count++;  //each time if the word of sentence matches with word given in profane_list then 1 is added to count

               System.out.println("The word " + profane + " is a profane!");  //displays the word which is profane

           }  }    }

   System.out.println("Number of profane words: "+ count);  }  //displays the number of profane words found in the sentence

private static List<String> profaneList() {  //list of profane words

   List<String> profane_words =  new ArrayList<>();  //creates an array list of profane words named as profane_words

   profane_words.add("dog");  //adds word "dog" to the list of profane words

   profane_words.add("cat");  //adds word "cat" to the list of profane words

   profane_words.add("llama");  //adds word "llama" to the list of profane words

   return profane_words;  }} //returns the list of profane words

Explanation:

I will explain the program with an example:

sentence = "CaT and catalog are not same";  

First this sentence is converted to lower case as:

sentence = "cat and catalog are not same";  

Now the while loop uses hasNext() which keeps returning the next token and that token is stored in word variable.

Next the for loop iterates through the list of profane_words to check each profane word with the word in a sentence.

Next this statement:

if (word.matches(".*\\b" + profane + "\\b.*") && ! sentence.matches(".*" + profane + "[a-z].*\\b" + profane + "\\b.*") && ! sentence.matches(".*[a-z]" + profane + ".*\\b" + profane + "\\b.*"))

uses regular expressions to find the profane words in the sentence. The logical operator&& AND between the three expressions is used so all of the three must hold for the if condition to evaluate to true.

word.matches(".*\\b" + profane + "\\b.*")  expression uses \b to check an exact match of the word. \b is meta-character to find a match at the beginning and at the end. So this checks if the word of a sentence matches with the profane in the profane list.

! sentence.matches(".*" + profane + "[a-z].*\\b" + profane + "\\b.*") && ! sentence.matches(".*[a-z]" + profane + ".*\\b" + profane + "\\b.*"))

These two expressions check if profane does not include as a part of another word in the sentence. This solves the extra challenge. Like here in the sentence we have a word catalog which is not a profane but a profane cat is included in this. So this will not be considered as a profane.

Every time a word matches with the profane from profane list, the value of count variable is incremented to 1.

In the end the statement:    

System.out.println("Number of profane words: "+ count);  

prints the number of profane words in the sentence.

List<String> profane_words =  new ArrayList<>(); creates the list of profane words and add() method adds the words to the list profane_words. So profane_words list contain "cat", "dog" and "llama"

Hence the output of this program is:

The word cat is a profane!                                                                                                                      Number of profane words: 1

The program output is attached in screenshot