Java Program to Swap two Strings Without Using any Third Variable

30 Sep, 2021
Given two string variables, a and b, your task is to write a Java Program to swap these variables without using any temporary or third variable. Use of library methods is allowed.
Examples: 
Input: a = "Hello"
       b = "World"

Output:
Strings before swap: a = Hello and b = World
Strings after swap: a = World and b = Hello
Method: In order to swap two string variables without using any temporary or third variable, the idea is to use string concatenation and substring() methods to perform this operation. The substring() method comes in two forms, as listed below: 
substring(int beginindex): This function will return the substring of the calling string starting from the index passed as an argument to this function till the last character in the calling string. 
substring(int beginindex, int endindex): This function will return Substring of the calling string starting from the beginindex(inclusive) and ending at the endindex(exclusive) passed as an argument to this function.  
Algorithm: 
1) Append second string to first string and 
   store in first string:
   a = a + b

2) call the method substring(int beginindex, int endindex)
   by passing beginindex as 0 and endindex as,
      a.length() - b.length():
   b = substring(0,a.length()-b.length());

3) call the method substring(int beginindex) by passing 
   b.length() as argument to store the value of initial 
   b string in a
   a = substring(b.length());
Code:
Java
// Java program to swap two strings without using a temporary// variable.import java.util.*;  class Swap{        public static void main(String args[])    {        // Declare two strings        String a = "Hello";        String b = "World";                  // Print String before swapping        System.out.println("Strings before swap: a = " +                                        a + " and b = "+b);                  // append 2nd string to 1st        a = a + b;                  // store initial string a in string b        b = a.substring(0,a.length()-b.length());                  // store initial string b in string a        a = a.substring(b.length());                  // print String after swapping        System.out.println("Strings after swap: a = " +                                      a + " and b = " + b);            }    }
Strings before swap: a = Hello and b = World
Strings after swap: a = World and b = Hello
This article is contributed by Harsh Agarwal. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect or you want to share more information about the topic discussed above.
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