Question

private static void changeString(String s) {
    s = new String("new string");
}

public static void main(String[] args) {
    String s = new String("old string");
    changeString(s);
    System.out.println(s); // expect "new string"
}

How could I make the output of “new string” happen with s as the only argument to method changeString?

thanks.

Answer 1

In Java arguments are passed by value, object arguments pass a reference to the object, this means that you can change the reference of the argument, but that does not change the object you passed the reference to. You have two possibilities, return the new object (preferred) or pass reference to a container that can receive the new reference (collection, array, etc.) For example:

private static String changeStringAndReturn(String s) {
    return new String("new string");
}
private static void changeStringInArray(String[] s) {
    if (null != s && 0 < s.length) {
        s[0] = new String("new string");
    }
}