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1.java

public record Box(int size) implements Item {}

public record Container(Item[] items) implements Item { }

2.java

public class WeightCalculator {
    public int calculate(Box box) {
        return box.size();
    }
    public int calculate(Container container) {
        int sum = 2;
        for (Item item : container.items()) {
            sum += calculate(item); // [!] Cannot resolve method 'calculate(Item)'
        }
        return sum;
    }
}