String Questions

1. Different ways to reverse a string

Description: Reverse the given string and print the characters in reverse order.
Input: Code Java Mastery
Output: yretsaM avaJ eroC

Reverse a String with For Loop

public class ReverseString1 {
    public static void main(String arg[]){
        String str="Core Java Mastery";
        String rev="";
        for(int i=str.length()-1; i>=0; i--){
            rev = rev + str.charAt(i);
        }
        System.out.println("Reversed string is: "+ rev);
    }
}

Reverse a String with While Loop

public class ReverseString2 {
    public static void main(String[] args) {
        String str="Core Java Mastery";
        String rev="";
        int i = str.length()-1;
        while(i>=0){
            rev = rev+str.charAt(i);
            i--;
        }
        System.out.println(rev);
    }
}

Reverse a String with do while Loop

public class ReverseString12 {
    public static void main(String[] args) {
        String str = "Core Java Mastery";
        String rev = "";

        int i = str.length() - 1;

        do {
            rev = rev + str.charAt(i);
            i--;
        } while (i >= 0);

        System.out.println("Reversed string is: " + rev);
    }
}

Reverse a String with StringBuilder reverse method

public class ReverseString3 {
    public static void main(String[] args) {
        String str = "Core Java Mastery";
        String rev = new StringBuilder(str).reverse().toString();
        System.out.println("Reversed string is: " + rev);
    }
}

Reverse a String with char array

public class ReverseString4 {
    public static void main(String[] args) {
        String str = "Core Java Mastery";

        char[] arr = str.toCharArray();

        for(int i = arr.length - 1; i >= 0; i--) {
            System.out.print(arr[i]);
        }
    }
}

Reverse a String with recursion

public class ReverseString5 {

    public static String reverse(String str) {
        if(str.isEmpty())
            return str;

        return reverse(str.substring(1)) + str.charAt(0);
    }

    public static void main(String[] args) {
        String str = "Core Java Mastery";

        System.out.println("Reversed string is: " + reverse(str));
    }
}

Reverse a String with stream

public class ReverseString6 {
    public static void main(String[] args) {
        String str = "Core Java Mastery";

        String reversed = IntStream.range(0, str.length())
                .mapToObj(i -> str.charAt(str.length() - 1 - i))
                .collect(StringBuilder::new,
                        StringBuilder::append,
                        StringBuilder::append)
                .toString();

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

Reverse a String with collection reverse

public class ReverseString7 {
    public static void main(String[] args) {
        String str = "Core Java Mastery";

        List<Character> list = new ArrayList<>();

        for(char c : str.toCharArray()) {
            list.add(c);
        }

        Collections.reverse(list);

        StringBuilder rev = new StringBuilder();
        for(char c : list) {
            rev.append(c);
        }

        System.out.println("Reversed string is: " + rev);
    }
}

Reverse a String with StringBuffer

public class ReverseString8 {
    public static void main(String[] args) {
        String str = "Core Java Mastery";

        String reversed = new StringBuffer(str).reverse().toString();

        System.out.println(reversed);
    }
}

Reverse a String Using Two Pointer Technique (Swap)

public class ReverseString9 {
    public static void main(String[] args) {
        String str = "Core Java Mastery";

        char[] arr = str.toCharArray();

        int start = 0;
        int end = arr.length - 1;

        while(start < end) {
            char temp = arr[start];
            arr[start] = arr[end];
            arr[end] = temp;

            start++;
            end--;
        }

        System.out.println(new String(arr));
    }
}

Reverse a String Using Stack

public class ReverseString10 {
    public static void main(String[] args) {
        String str = "Core Java Mastery";

        Stack<Character> stack = new Stack<>();

        for(char c : str.toCharArray()) {
            stack.push(c);
        }

        while(!stack.isEmpty()) {
            System.out.print(stack.pop());
        }
    }
}

Reverse a String Using reduce() in Stream

public class ReverseString11 {
    public static void main(String[] args) {
        String str = "Core Java Mastery";

        String reversed = Stream.of(str.split(""))
                .reduce("", (a, b) -> b + a);

        System.out.println(reversed);
    }
}