Question

I know that Java strings are immutable. However, when I run the function below, the output is not what I expect it to be.

    public static void main(String[] args) {
        String s = "wicked";
        String [] ss = new String [1];
        ss[0] = "witch";
        modify(s, ss);
        System.out.println(s+" "+ ss[0]);
    }
    private static void modify(String s, String[] ss) {
        s = "sad";
        ss[0] = "sod";          
    }

The output I get is wicked sod, and not wicked witch as I expected it to be. Is it because I am passing an array reference as the second argument to the modify function as opposed to passing the String object itself? Any clarification is highly appreciated.

Answer 1

You’ve changed the contents of the array – arrays are always mutable.

The array initially contains a reference to the string “witch”. Your modify method changes the array to contain a reference to the string “sod”. None of the strings themselves have been changed – just the contents of the array.

(Note that the value of ss[0] isn’t a string – it’s a reference to a string.)