第 52 条：慎用重载

慎用重载.jpeg

// Broken! - What does this program print?
public class CollectionClassifier {
    public static String classify(Set<?> s) {
        return "Set";
    }
    public static String classify(List<?> lst) {
        return "List";
    }
    public static String classify(Collection<?> c) {
        return "Unknown Collection";
    }
    public static void main(String[] args) {
        Collection<?>[] collections = {
            new HashSet<String>(),
            new ArrayList<BigInteger>(),
            new HashMap<String, String>().values()
        };
        for (Collection<?> c : collections)
            System.out.println(classify(c));
    }
}



public static String classify(Collection<?> c) {
    return c instanceof Set ? "Set" : c instanceof List ? "List" : "Unknown Collection";
}