How to swap two string variables in Java without using a third variable

Question

How do I swap two string variables in Java without using a third variable, i.e. the temp variable?

String a = \"one\"
String b = \"two\"
String temp = null;
temp         


        

Answer 1

public class ex{
    public static void main(String[] args){

        String s1="abc";
        String s2="def";

        System.out.println(s1);
        System.out.println(s2);

        s3=s2.replaceAll(s1,s2=s1);

        System.out.println(s1);
        System.out.println(s2);

    }
}

Answer 2

// taken from this answer: https://stackoverflow.com/a/16826296/427413

String returnFirst(String x, String y) {
    return x;
}

String a = "one"
String b = "two"
a = returnFirst(b, b = a); // If this is confusing try reading as a=b; b=a;

This works because the Java language guarantees (Java Language Specification, Java SE 7 Edition, section 15.12.4.2) that all arguments are evaluated from left to right (unlike some other languages, where the order of evaluation is undefined), so the execution order is:

1. The original value of b is evaluated in order to be passed as the first argument to the function
2. The expression b = a is evaluated, and the result (the new value of b) is passed as the second argument to the function
3. The function executes, returning the original value of b and ignoring its new value
4. You assing the result to a
5. Now the values have been swapped and you didn't need to declare temp. The parameter x works as temp, but it looks cleaner because you define the function once and you can use it everywhere.

Answer 3

• Actually, the code in your question did not swap String a,b.

  You should see this issue: Swap two strings in Java, by passing them to a utility function, but without returning objects or using wrapper classes

• And Java is passing by value: Is Java "pass-by-reference" or "pass-by-value"?

Answer 4

package com.core;

public class SwappingNoTemp {

public static void main(String[] args) {

    String a = "java";
    String b = "c";

    a = a + b;

    b = a.substring(0, a.length() - b.length());
    a = a.substring(b.length());

    System.out.println("swapping is a.." + a);
    System.out.println("swapping  is b.." + b);

}

}

Answer 5

I'd just like to point out, just in case anyone looks through this thread. There is no way of swapping two strings without using a third variable. In the java examples, since strings are immutable, a=a+b creates a third string, and doesn't reassign a. Doing the reverseString, creates a new variable, but this time on the stack frame as the program goes into a new scope. The use of Xor swapping might work, but Strings are immutable in java, and so xor swaps will also create a temporary variable. So in fact, unless the language enables you to reassign to the same memory space, it isn't possible to swap strings without creating new variables.

Answer 6

For strings:

String a = "one"
String b = "two"

a = a + b;
b = a.replace(b, "");
a = a.replace(b, "");