wildcards

public class MagicBox<T> {
    private T item;

    public void addItem(T item) {
        this.item = item;
        System.out.println("Added item to the magic box: " + item);
    }

    public T getItem() {
        return item;
    }

    public void processBox(MagicBox<? super Integer> box) {
        System.out.println("Items in the box are processed [" + box.getItem() + "]");
    }

    public static void main(String[] args) {
        MagicBox<Integer> integerBox = new MagicBox<>();
        integerBox.addItem(43);
        
        MagicBox<String> stringBox = new MagicBox<>();
        stringBox.addItem("Sofiya");
        
        MagicBox<Boolean> booleanBox = new MagicBox<>();
        booleanBox.addItem(false);
        
        MagicBox<Object> objectBox = new MagicBox<>();
        objectBox.addItem(43.43);

        // Using processBox with a MagicBox that can accept Integer or its supertypes
        integerBox.processBox(integerBox);
        integerBox.processBox(objectBox);

        // The following lines will cause compilation errors as they don't match the processBox parameter type
        // integerBox.processBox(stringBox);
        // integerBox.processBox(booleanBox);
    }
}