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Swap two strings in Java, by passing them to a utility function, but without returning objects or using wrapper classes

Asked 2010-09-13T06:52:48.500
9

I am trying to swap two strings in Java. I never really understood "strings are immutable". I understand it in theory, but I never came across it in practice.

Also, since String is an object in Java and not a primitive type, I don't understand why the following code prints the same result twice, instead of interchanging the words!

public static void main(String[] args)
{
    String s1 = "Hello";
    String s2 = "World";

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

    Swap(s1, s2);

    System.out.println(s1 + " " + s2);
}

public static void Swap(String s1, String s2)
{
    String temp = s1;
    s1 = s2;
    s2 = temp;
}

I want it to print

Hello World
World Hello

But it is printing

Hello World
Hello World

I thought s1 and s2 are references and hence the references should be swapped and the new ones should point to the other one respectively. Where am I going wrong?

java string pass-by-reference
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2 Answers

2

Java Strings are implemented with references, so you need to swap their references.

String s1 = "Hello";
String s2 = "World";
AtomicReference<String> String1 = new AtomicReference<String>(s1);
AtomicReference<String> String2 = new AtomicReference<String>(s2);
String1.set(String2.getAndSet(String1.get()));
System.out.println(String1 + " " + String2);

It will give you this output:

World Hello
answered 2012-02-28T12:28:24.963
1
String s1 = "Hello";
String s2 = "World";
    s1=s1+" "+s2;
s2=s1.split(" ")[0];
s1=s1.split(" ")[1];
System.out.println(s1 + " " + s2);
answered 2012-08-29T06:44:38.073

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