Input: str = “Java”

Output: aJva

Explanation: The given string contains even number of characters. Therefore, we swap every pair of characters.



Input: str = “GeeksForGeeks”

Output: eGkeFsroeGkes

Explanation: The given string contains odd number of characters. Therefore, we swap every pair of characters and last character remains as it is.

1. Using String.toCharArray() Method

// Java program to swap pair
// of characters of a string

class GFG {

	// Function to swap pair of
	// characters of a string
	public static String swapPair(String str)
	{

		// Checking if string is null
		// or empty then return str
		if (str == null || str.isEmpty())
			return str;

		// Converting the given string
		// into a character array
		char[] ch = str.toCharArray();

		// Traverse the character array
		for (int i = 0; i < ch.length - 1; i += 2) {

			// Swapping the characters
			char temp = ch[i];
			ch[i] = ch[i + 1];
			ch[i + 1] = temp;
		}

		// Converting the result into a
		// string and return
		return new String(ch);
	}

	// Driver Code
	public static void main(String args[])
	{

		// Given String str
		String str = "GeeksForGeeks";

		// Print the result
		System.out.println(swapPair(str));
	}
}

Output

eGkeFsroeGkes

2. Using StringBuffer.append() Method

// Java program to swap pair
// of characters of a string

class GFG {

	// Function to swap pair of
	// characters of a string
	public static String swapPairs(String str)
	{

		// Checking if string is null
		// or empty then return str
		if (str == null || str.isEmpty())
			return str;

		int len = str.length();

		// Creating a StringBuffer object with
		// length of the string passed as a parameter
		StringBuffer sb = new StringBuffer(len);

		// Traverse the string and append
		// the character in the StringBuffer
		// object in reverse order
		for (int i = 0; i < len - 1; i += 2) {
			sb.append(str.charAt(i + 1));
			sb.append(str.charAt(i));
		}

		// Checking if the string has
		// odd number of characters
		// then append the last character
		// into StringBuffer object
		if (len % 2 != 0) {
			sb.append(str.charAt(len - 1));
		}

		// Converting the StringBuffer
		// into the string and return
		return sb.toString();
	}

	// Driver Code
	public static void main(String args[])
	{

		// Given String str
		String str = "GeeksForGeeks";

		// Print the result
		System.out.println(swapPairs(str));
	}
}

Output

eGkeFsroeGkes