In this article, there are two ways used to achieve the solution, using Map and using String Array.

1. Java Program to find occurrences of the duplicate words in a sequence of string without using Map

Program:

class DuplicateWordsWithoutUsingMap {
    public static void main(String[] args) {
        String str = " this is is the word this is this";
        int count;
        String duplicates = "";
        String[] words = str.toLowerCase().trim().split(" ");
        for (int i = 0; i < words.length; i++) {
            count = 1;
            for (int j = i + 1; j < words.length; j++) {
                if (words[i].equals(words[j])) {
                    count++;
                }
            }
            if (count > 1) {
                if (duplicates.isEmpty()) {
                    duplicates += " " + words[i] + " : " + count;
                } else if (!duplicates.matches("(.*) " + words[i] + " (.*)")) {
                    duplicates += " " + words[i] + " : " + count;
                }
            }
        }
        System.out.println(duplicates);
    }
}

Output:

2. Java Program to find occurrences of the duplicate words in a sequence string with the help of Map

Program:

class DuplicateWords {
    public static void main(String[] args) {
        String str = "This is a program to find duplicate words in a string, again! a program";
        String[] words = str.toLowerCase().trim().split(" ");
        Map<String, Integer> duplicateString = new HashMap<>();
        int count = 1;
        for (String x : words) {
            if (duplicateString.containsKey(x)) {
                duplicateString.put(x, duplicateString.get(x) + 1);
            } else {
                duplicateString.put(x, count);
            }
        }
        System.out.println("Duplicate Words in a String : ");
        for (Map.Entry a : duplicateString.entrySet()) {
            int val = (Integer) a.getValue();
            if (val > 1) {
                System.out.println(a);
            }
        }
    }
}

Output:

Duplicate Words in a String : 
a=3
program=2