Swapping Pairs of Characters in a String in Java

Last Updated : 20 Feb, 2024

Given string str, the task is to write a Java program to swap the pairs of characters of a string. If the string contains an odd number of characters then the last character remains as it is.

Examples:

Input: str = “Java”
Output: aJav

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

Get the string to swap a pair of characters.
Check if the string is null or empty then return the string.
Converting the given string into a character array.
Traverse the character array and swap the characters.
Now, print the result.

Java

// 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

Get the string to swap a pair of characters.
Check if the string is null or empty then return the string.
Creating a StringBuffer object with a length of the string passed as a parameter.
Traverse the string and append the characters in the StringBuffer object in reverse order.
Check if the string contains an odd number of characters then append the last character into the StringBuffer object.
Now, print the result.

Java

// 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));  } }