Swapping Pairs of Characters in a String in Java

Swapping characters within a string is a common operation in Java programming, involving rearranging individual characters to achieve a desired order. The process holds significance in various scenarios, such as data encryption, algorithmic transformations, or enhancing string manipulation capabilities within Java applications.

Let's Explore various Java methods for character swapping and string generation.

Method 1 (Using toCharArray)

The Method involves converting the input string into a character array using the toCharArray Method, allowing direct manipulation of characters. It is suitable for scenarios where character-level modifications are needed.

Filename: StringSwapperDemo.java

public class StringSwapperDemo {

    // Method to swap characters at given positions in a string
    static String swapCharacters(String inputString, int position1, int position2) {
        // Create a StringBuilder to modify the string
        StringBuilder stringBuilder = new StringBuilder(inputString);
        
        // Swap characters at the specified positions
        char temp = stringBuilder.charAt(position1);
        stringBuilder.setCharAt(position1, stringBuilder.charAt(position2));
        stringBuilder.setCharAt(position2, temp);
        
        // Convert StringBuilder back to String and return
        return stringBuilder.toString();
    }

    // Main Method, the entry point of the program
    public static void main(String args[]) {
        // Original string
        String originalString = "javatpoint";

        // Example 1: Swap characters at positions 6 and (length - 2)
        String swappedString1 = swapCharacters(originalString, 6, originalString.length() - 2);
        System.out.println("After swapping characters at positions 6 and " + (originalString.length() - 2) + ": " + swappedString1);

        // Example 2: Swap characters at positions 0 and (length - 1)
        String swappedString2 = swapCharacters(originalString, 0, originalString.length() - 1);
        System.out.println("After swapping characters at positions 0 and " + (originalString.length() - 1) + ": " + swappedString2);

        // Display the original string
        System.out.println("Original String: " + originalString);
    }
}

Output:

After swapping characters at positions 6 and 8: javatpniot
After swapping characters at positions 0 and 9: tavatpoinj
Original String: javatpoint

Method 2 (Using subString())

Utilizing the substring() Method, this Method extracts and manipulates substrings within the input string, making it helpful for swapping pairs of characters or performing specific operations on portions of the string.

Filename: StringSwapperExample.java

// Class for demonstrating character swapping using XOR operation
public class StringSwapperExample {

    //Method to swap characters in a string using XOR operation
    static String swapCharacters(String input, int index1, int index2) {
        // Convert input string to char array
        char[] characters = input.toCharArray();

        // XOR swap operation
        characters[index1] = (char)(characters[index1] ^ characters[index2]);
        characters[index2] = (char)(characters[index1] ^ characters[index2]);
        characters[index1] = (char)(characters[index1] ^ characters[index2]);

        // Convert back to string and return
        return String.valueOf(characters);
    }

    // Main Method
    public static void main(String args[]) {
        // Original input string
        String originalString = "javatpoint";

        // Swap characters at indices 6 and (length - 2)
        System.out.println("After swapping characters at indices 6 and " + (originalString.length() - 2) +
                ": " + swapCharacters(originalString, 6, originalString.length() - 2));

        // Swap first and last characters
        System.out.println("After swapping first and last characters: " +
                swapCharacters(originalString, 0, originalString.length() - 1));

        // Original String doesn't change
        System.out.println("Original String: " + originalString);
    }
}

Output:

After swapping characters at indices 6 and 8: javatpniot
After swapping first and last characters: tavatpoinj
Original String: javatpoint

Method 3 (Using StringBuilder or StringBuffer)

The technique utilizes the mutable StringBuilder or StringBuffer class, offering efficiency in string manipulations, especially for scenarios where multiple modifications are required in a string. It provides a dynamic and memory-efficient solution compared to immutable strings, allowing for in-place modifications.

Filename: StringBuilderStringSwapper.java

public class StringBuilderStringSwapper {

    //Method to swap characters in a string using StringBuilder
    static String swapCharacters(String input, int index1, int index2) {

        // Check if the provided indices are valid
        if (isValidIndex(input, index1) && isValidIndex(input, index2)) {

            // Create a StringBuilder from the input string
            StringBuilder sb = new StringBuilder(input);

            // Swap characters using StringBuilder
            char temp = sb.charAt(index1);
            sb.setCharAt(index1, sb.charAt(index2));
            sb.setCharAt(index2, temp);

            // Convert StringBuilder back to a string and return
            return sb.toString();
        } else {
            // Handle invalid indices
            System.out.println("Invalid indices provided. No swapping performed.");
            return input;
        }
    }

    // Helper method to check if an index is within the valid range
    static boolean isValidIndex(String input, int index) {
        return index >= 0 && index < input.length();
    }

    public static void main(String args[]) {
        // Original string
        String originalString = "javatpoint";

        // Swap characters at indices 3 and 8
        int index1 = 3;
        int index2 = 8;
        String swappedString1 = swapCharacters(originalString, index1, index2);
        System.out.println("After swapping characters at indices " + index1 + " and " + index2 + ": " + swappedString1);

        // Swap first and last characters
        int firstIndex = 0;
        int lastIndex = originalString.length() - 1;
        String swappedString2 = swapCharacters(originalString, firstIndex, lastIndex);
        System.out.println("After swapping first and last characters: " + swappedString2);

        // Original String doesn't change
        System.out.println("Original String: " + originalString);
    }
}

Output:

After swapping characters at indices 3 and 8: javntpoiat
After swapping first and last characters: tavatpoinj
Original String: javatpoint

Method 4 (Using XOR Operator)

In this Method, characters are swapped using the XOR operator, which is a bitwise exclusive OR operation. It provides a concise way to exchange values without a temporary variable, making it an interesting and bitwise-efficient approach for swapping characters.

Filename: StringSwapperXOR.java

public class StringSwapperXOR {

    static String swapCharacters(String input, int index1, int index2) {
        if (isValidIndex(input, index1) && isValidIndex(input, index2)) {
            char[] characters = input.toCharArray();

            char temp = characters[index1];
            characters[index1] = characters[index2];
            characters[index2] = temp;

            return String.valueOf(characters);
        } else {
            // Handle invalid indices
            System.out.println("Invalid indices provided. No swapping performed.");
            return input;
        }
    }

    static boolean isValidIndex(String input, int index) {
        return index >= 0 && index < input.length();
    }

    public static void main(String args[]) {
        String originalString = "javatpoint";

        // Swap characters at indices 3 and 8
        int index1 = 3;
        int index2 = 8;
        String swappedString1 = swapCharacters(originalString, index1, index2);
        System.out.println("After swapping characters at indices " + index1 + " and " + index2 + ": " + swappedString1);

        // Swap first and last characters
        int firstIndex = 0;
        int lastIndex = originalString.length() - 1;
        String swappedString2 = swapCharacters(originalString, firstIndex, lastIndex);
        System.out.println("After swapping first and last characters: " + swappedString2);

        // Original String doesn't change
        System.out.println("Original String: " + originalString);
    }
}

Output:

After swapping characters at indices 3 and 8: javntpoiat
After swapping first and last characters: tavatpoinj
Original String: javatpoint

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Swapping Pairs of Characters in a String in Java

Method 1 (Using toCharArray)

Method 2 (Using subString())

Method 3 (Using StringBuilder or StringBuffer)

Method 4 (Using XOR Operator)

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