Java Programs for Exception Handling and Collections

Problem 1: Reverse Words using Queue


import java.util.*;
class Main {
    static String reverseWords(String str) {
        Queue queue = new LinkedList<>();
        String[] words = str.split("\\s+");   
        for (String word : words) {
            queue.add(word);
        }
        StringBuilder result = new StringBuilder();
        while (!queue.isEmpty()) {
            result.insert(0, queue.poll() + " "); 
        }

        return result.toString().trim();
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.nextLine();
        System.out.println(reverseWords(str));
    }
}

Problem 2: First Non-Repeating Character using Queue


import java.util.*;
class Main {
static char firstNonRepeating(String str) {
        Queue queue = new LinkedList<>();
        Map map = new HashMap<>();
        for (char c : str.toCharArray()) {
            map.put(c, map.getOrDefault(c, 0) + 1);
            queue.add(c);
        }
        while (!queue.isEmpty()) {
            char c = queue.poll();
            if (map.get(c) == 1) {
                return c;
            }
        }
        return ' ';
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.nextLine();
        char result = firstNonRepeating(str);
        if (result == ' ') {
            System.out.println("No non-repeating character");
        } else {
            System.out.println(result);
        }
    }
    }

Problem 3: Word Frequency Counter using Map


import java.util.*;
             class Main {
    static void countWordFrequency(String paragraph) {
        Map wordMap = new LinkedHashMap<>();
        String[] words = paragraph.toLowerCase().replaceAll("[^a-z\\s]", "").split("\\s+");
        for (String word : words) {
            wordMap.put(word, wordMap.getOrDefault(word, 0) + 1);
        }
        for (Map.Entry entry : wordMap.entrySet()) {
            System.out.println(entry.getKey() + " " + entry.getValue());
        }
    }
            public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String paragraph = sc.nextLine();
        countWordFrequency(paragraph);
    }
}

Problem 4: Character Frequency Counter using Map



import java.util.*;
class Main {
    static void countCharacterFrequency(String str) {
        Map map = new LinkedHashMap<>();
        for (char c : str.toCharArray()) {
            map.put(c, map.getOrDefault(c, 0) + 1);
        }
        for (Map.Entry entry : map.entrySet()) {
            System.out.println(entry.getKey() + " " + entry.getValue());
        }
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.nextLine();
        countCharacterFrequency(str);
    }
}

Problem 5: Division with Exception Handling


import java.util.*;
class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        try {
            System.out.println("Enter numerator (a):");
            int a = sc.nextInt();
            System.out.println("Enter denominator (b):");
            int b = sc.nextInt();
            int result = a / b;
            System.out.println("Result: " + result);
        } catch (ArithmeticException e) {
            System.out.println("Error: Division by zero is not allowed.");
        } catch (InputMismatchException e) {
            System.out.println("Error: Invalid input. Please enter integers only.");
        }
    }
}

}

Problem 6: Array Index Access with Exception Handling


import java.util.*;
class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        try {
            System.out.println("Enter size of array:");
            int n = sc.nextInt();
            int[] arr = new int[n];
            System.out.println("Enter " + n + " elements:");
            for (int i = 0; i < n; i++) {
                arr[i] = sc.nextInt();
            }
            System.out.println("Enter the index to access:");
            int index = sc.nextInt();
            System.out.println("Value at index " + index + ": " + arr[index]);
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("Error: Index out of bounds.");
        } catch (InputMismatchException e) {
            System.out.println("Error: Invalid input. Please enter integers only.");
        }
    }

}

Problem 7: Reverse List using Collections


import java.util.*;

class Main {

   public static void main(String[] args) {

       Scanner sc = new Scanner(System.in);

       System.out.println("Enter number of elements:");

       int n = sc.nextInt();

       List list = new ArrayList<>();

       System.out.println("Enter elements:");

       for (int i = 0; i < n; i++) {

           list.add(sc.nextInt());

       }

       Collections.reverse(list);

       for (int num : list) {

           System.out.print(num + " ");

       }

   }}

Problem 8: Find Intersection of Two Sets



import java.util.*;
class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter number of elements in first set:");
        int n1 = sc.nextInt();
        Set set1 = new HashSet<>();
        System.out.println("Enter elements:");
        for (int i = 0; i < n1; i++) {
            set1.add(sc.nextInt());
        }
        System.out.println("Enter number of elements in second set:");
        int n2 = sc.nextInt();
        Set set2 = new HashSet<>();
        System.out.println("Enter elements:");
        for (int i = 0; i < n2; i++) {
            set2.add(sc.nextInt());
        }
        set1.retainAll(set2);
        for (int num : set1) {
            System.out.print(num + " ");
        }
    }
}