Java: how to require subclasses to call super() when super's argument is a vararg

Question

I have an abstract class which has a constructor that takes varargs. The Java compiler doesn't seem to require that child classes call super() even though every constructor takes arguments.

public abstract class Parent {
    public Parent(String... varargs) {

    }
}

public class Child extends Parent {
    // I would like this to be a compile error. Child should always call super().
}

How can I write Parent so that children must call super()?

Answer 1

The purpose of a varargs method is to allow the programmer to write each argument individually, so it's possible to prepend a required argument of the same type to make sure at least one is passed in. For callers that have a list or array, an alternate constructor can accept Iterable.

public abstract class Parent2 {
    public Parent2(String firstArg, String... varargs) {

    }

    public Parent2(Iterable<? extends String> args) {

    }
}

public class Child2 extends Parent2 {
    public Child2() {
        super("abc");
    }
}

Answer 2

From the docs, the number of parameters passed to a method/constructor accepting a varargs parameter, can be none, making the constructor act as a default parameter less constructor too.

To use varargs, you follow the type of the last parameter by an ellipsis (three dots, ...), then a space, and the parameter name. The method can then be called with any number of that parameter, including none.

So you could change it to an array,

abstract class Parent {
    public Parent(String[] varargs) {

    }
}

your child constructor would be forced to call this constructor explicitly.