Use strtok() to split the string into words. Now each word uses two pointers, i and j point to the penultimate character and the penultimate character of the string, respectively. Swap these characters, then increase i and decrease j. Repeat these steps when i <j. The following is the implementation of the above method:

str[i] = Character obtained after traversing ascii(str[i]) no. of characters in ‘a-z’ repeatedly after str[i].

Examples: 

Input: str = “geeksforgeeks” 
Output: fbbnddvbfbbnd
In the above case str = “geeksforgeeks”, 
the ASCII value of ‘g’ is 103 therefore ‘g’ has been replaced by moving 103 times from ‘g’ in the desired range i.e., a-z. 
Hence, character ‘g’ is replaced by ‘f’. 
Similarly, the complete string “geeksforgeeks” becomes “fbbnddvbfbbnd”.
Input: str = “science” 
Output: dxjbtxb

Approach: 

1. Traverse the string.
2. For every i, find the character that needs to be replaced with str[i].
3. Replace str[i] with that character.

Below is the implementation of above approach: 

// Java program for Replace every character of a
// string by a different character
public class GFG {

	//Function to manipulate the string
	static void manipulateString(String str)
	{

		char[] str1 = str.toCharArray();
		
	// looping through each character of string
	for (int i = 0; i < str.length(); i++) {

		// storing integer ASCII value of
		// the character in 'asc'
		
		int asc = str1[i];
		
		// 'rem' contains coded value which
		// needs to be rounded to 26
		int rem = asc - (26 - (str1[i] - 97));

		// converting 'rem' character in range
		// 0-25 and storing in 'm'
		int m = rem % 26;
		
		// printing character by adding ascii value of 'a'
		// so that it becomes in the desired range i.e. a-z
		str1[i] = (char)(m + 'a');
			
	}
	
	String str2 = String.valueOf(str1);
	System.out.println(str2);
	
	}

	//Driver code
	public static void main(String[] args) {
		
		// Declaring str as 'geeksforgeeks'
		String str = "geeksforgeeks";

		manipulateString(str);
		
		
	}
}

Output: 

fbbnddvbfbbnd