Editing Comparison of C Sharp and Java (section)

==== Reference (in/out) parameters ====
The arguments of primitive types (e.g. int, double) to a method are passed by value in Java whereas objects are passed by reference. This means that a method operates on copies of the primitives passed to it instead of on the actual variables. On the contrary, the actual objects in some cases can be changed. In the following example, object String is not changed. Object of class 'a' is changed.

In C#, it is possible to enforce a reference with the {{mono|ref}} keyword, similar to C++ and in a sense to C. This feature of C# is particularly useful when one wants to create a method that returns more than one object. In Java trying to return multiple values from a method is unsupported unless a wrapper is used, in this case named "Ref".<ref>{{cite web |url=http://www.25hoursaday.com/ |title=A Comparison of Microsoft's C# Programming Language to Sun Microsystems' Java Programming Language: D. Now for Something Completely Different: 12. Pass by Reference |author=Dare Obasanjo |year=2007 |publisher=Dare Obasanjo |archive-url=https://web.archive.org/web/20120919093308/http://25hoursaday.com/ |archive-date=19 September 2012 |quote=In Java the arguments to a method are passed by value meaning that a method operates on copies of the items passed to it instead of on the actual items. In C#, as in C++ and in a sense C, it is possible to specify that the arguments to a method actually be references to the items being passed to the method instead of copies. This feature is particularly useful when one wants to create a method that returns more than one object. In Java trying to return multiple values from a method is unsupported and leads to anomalies like: a method that swaps two numbers that have been the hallmark of freshman computer science classes for years, is impossible to do in Java without resorting to coding tricks. |access-date=10 September 2012 |url-status=dead |df=dmy-all}}</ref>

{| style="width:100%; border:none;" class="wikitable"
|-
!width=50%| Java !! style="width:50%;"| C#
|- valign=top
| <syntaxhighlight lang="java" style="font-size:95%">
class PassByRefTest {

    static class Ref<T> {
        T val;
        Ref(T val) { this.val = val; }
    }
    
    static void changeMe(Ref<String> s) {
        s.val = "Changed";
    }

    static void swap(Ref<Integer> x, Ref<Integer> y) {
        int temp = x.val;

        x.val = y.val;
        y.val = temp;
    }

    public static void main(String[] args) {
        var a = new Ref(5);
        var b = new Ref(10);
        var s = new Ref("still unchanged");
        
        swap(a, b);
        changeMe(s);

        System.out.println( "a = " + a.val + ", " +
                            "b = " + b.val + ", " +
                            "s = " + s.val );
    }
}
</syntaxhighlight> 
| <syntaxhighlight lang="csharp" style="font-size:95%">
class PassByRefTest 
{
    public static void ChangeMe(out string s) 
    {
        s = "Changed";
    }

    public static void Swap(ref int x, ref int y) 
    {
        int temp = x;

        x = y;
        y = temp;
    }

    public static void Main(string[] args) 
    {
        int a = 5;
        int b = 10;
        string s = "still unchanged";

        Swap(ref a, ref b);
        ChangeMe(out s);

        System.Console.WriteLine("a = " + a + ", " +
                                 "b = " + b + ", " +
                                 "s = " + s);
    }
}</syntaxhighlight>
|- valign=top
| {{code|1=a = 10, b = 5, s = Changed}} || {{code|1=a = 10, b = 5, s = Changed}}
|}