How to concatenate variable arguments of string

Question

I need to concatenate a variable number of arguments (type String) to one String:

E.g.:

System.out.println( add("ja", "va") );

should return java but my implementation returns jaja.

I tried this:

public static String add(String... strings) {
    for (String arg : strings) {
        return String.format(arg.concat(arg));
    }
    return "string";
}

What am I doing wrong?

Answer 1

Nowadays you might want to use:

String.join(separator, strings)

Answer 2

You're returning on the first iteration of the loop (return String.format ...) rather than at the end. What you should use here is a StringBuilder:

public static String add(String... strings) {
    StringBuilder builder = new StringBuilder();
    for (String arg : strings) {
        builder.append(arg);
    }
    return builder.toString();  //Outputs the entire contents of the StringBuilder.
}