String Problems

Reverse a String

import java.util.Scanner;

public class ReverseString {
public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    System.out.print("Enter a string to reverse: ");
    String input = scanner.nextLine();
    String reversed = new StringBuilder(input).reverse().toString();
    System.out.println("Reversed string: " + reversed);
    scanner.close();
}
}

without using StringBuilder
import java.util.Scanner;

public class ReverseString {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter a string to reverse: ");
        String input = scanner.nextLine();

        // Manually reverse the string
        String reversed = "";
        for (int i = input.length() - 1; i >= 0; i--) {
            reversed += input.charAt(i);
        }

        System.out.println("Reversed string: " + reversed);
        
        scanner.close();
    }
}

************************************************************
Palindrome checking

import java.util.Scanner;

public class PalindromeChecker {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter a string to check if it is a palindrome: ");
        String input = scanner.nextLine();

        if (isPalindrome(input)) {
            System.out.println("The string \"" + input + "\" is a palindrome.");
        } else {
            System.out.println("The string \"" + input + "\" is not a palindrome.");
        }

        scanner.close();
    }

    public static boolean isPalindrome(String s) {
        int left = 0;
        int right = s.length() - 1;

        while (left < right) {
            if (s.charAt(left) != s.charAt(right)) {
                return false;
            }
            left++;
            right--;
        }

        return true;
    }
}

palindrome checking after reversing the string
import java.util.Scanner;

public class PalindromeChecker {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter a string to check if it is a palindrome: ");
        String input = scanner.nextLine();

        String reversed = reverseString(input);

        if (input.equals(reversed)) {
            System.out.println("The string \"" + input + "\" is a palindrome.");
        } else {
            System.out.println("The string \"" + input + "\" is not a palindrome.");
        }

        scanner.close();
    }

    public static String reverseString(String s) {
        String reversed = "";
        for (int i = s.length() - 1; i >= 0; i--) {
            reversed += s.charAt(i);
        }
        return reversed;
    }
}

**********************************************************************
Frequency of occurrence of a character in the string
 
import java.util.Scanner;

public class CharacterFrequencyCounter {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter a string: ");
        String input = scanner.nextLine();

        System.out.print("Enter the character to count: ");
        char characterToCount = scanner.next().charAt(0);

        int frequency = countCharacterFrequency(input, characterToCount);

        System.out.println("The character '" + characterToCount + "' appears " + frequency + " times in the string.");

        scanner.close();
    }

    public static int countCharacterFrequency(String s, char c) {
        int frequency = 0;

        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == c) {
                frequency++;
            }
        }

        return frequency;
    }
}
**********************************************
Analyse a String

import java.util.Scanner;

public class StringAnalyzer {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter a string: ");
        String input = scanner.nextLine();

        int length = input.length();
        int digitCount = 0;
        int lowercaseCount = 0;
        int uppercaseCount = 0;
        int specialCharCount = 0;

        for (int i = 0; i < input.length(); i++) {
            char c = input.charAt(i);
            if (Character.isDigit(c)) {
                digitCount++;
            } else if (Character.isLowerCase(c)) {
                lowercaseCount++;
            } else if (Character.isUpperCase(c)) {
                uppercaseCount++;
            } else {
                specialCharCount++;
            }
        }

        System.out.println("Length of the string: " + length);
        System.out.println("Number of digits: " + digitCount);
        System.out.println("Number of lowercase letters: " + lowercaseCount);
        System.out.println("Number of uppercase letters: " + uppercaseCount);
        System.out.println("Number of special characters: " + specialCharCount);

        scanner.close();
    }
}

***************************************************************
Caesar Cipher Encryption

import java.util.Scanner;

public class CaesarCipher {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter a string to encrypt: ");
        String input = scanner.nextLine();

        System.out.print("Enter the shift value: ");
        int shift = scanner.nextInt();

        String encrypted = encrypt(input, shift);

        System.out.println("Encrypted string: " + encrypted);

        scanner.close();
    }

    public static String encrypt(String text, int shift) {
        StringBuilder result = new StringBuilder();

        for (int i = 0; i < text.length(); i++) {
            char c = text.charAt(i);

            if (Character.isLetter(c)) {
                char base = Character.isLowerCase(c) ? 'a' : 'A';
                char encryptedChar = (char) ((c - base + shift) % 26 + base);
                result.append(encryptedChar);
            } else {
                result.append(c);
            }
        }

        return result.toString();
    }
}
**********************************************************************
Printing even length words in a sentence

public class EvenLengthWords {
    public static void main(String[] args) {
        String sentence = "This is a java language";
        String[] words = sentence.split(" ");
        for (String word : words) {
            if (word.length() % 2 == 0) {
                System.out.print(word + " ");
            }
        }
    }
}

*************************************************************************
Sorting names in alphabetical order

import java.util.Scanner;

class SortNames {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter the number of names: ");
        int n = scanner.nextInt();
        String names[] = new String[n];

        System.out.println("Enter the names:");
        for (int i = 0; i < n; i++) {
            names[i] = scanner.next();
        }

        String temp;
        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j < n; j++) {
                if (names[i].compareTo(names[j]) > 0) {
                    temp = names[i];
                    names[i] = names[j];
                    names[j] = temp;
                }
            }
        }

        System.out.println("The names in alphabetical order are:");
        for (int i = 0; i < n; i++) {
            System.out.println(names[i]);
        }
    }
}

using built in sort method
import java.util.Scanner;
import java.util.Arrays;

class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter the number of names: ");
        int n = scanner.nextInt();
        String names[] = new String[n];

        System.out.println("Enter the names:");
        for (int i = 0; i < n; i++) {
            names[i] = scanner.next();
        }

        Arrays.sort(names);

        System.out.println("The names in alphabetical order are:");
        for (int i = 0; i < n; i++) {
            System.out.println(names[i]);
        }
    }
}

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