Swap two Strings without using third user defined variable in Java

1.8

Given two string variables a and b, swap these variables without using temporary or third variable in Java. 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

The idea is to string concatenation and substring() method to perform this operation. The substring() method comes in two forms as listed below:

  • substring(int beginindex): This fuction will return substring of the calling string starting from the index passed as 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 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());
// 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 intial 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);        
    }    
}

Output:

Strings before swap: a = Hello and b = World
Strings after swap: a = World and b = Hello

References:
http://docs.oracle.com/

This article is contributed by Harsh Agarwal. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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