Problem with <T extends Comparable<? super T>>>

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Old 07-14-2011
Problem with <T extends Comparable<? super T>>>

Hi guys,

I have a three class:
1. Class Algorithm having max() finding maximum value in a Collection
public class Algorithm {
    public static <T extends Comparable<T>> T max(Collection<? extends T> coll) {
        T max = coll.iterator().next();

        for (T elm : coll) {
            if (max.compareTo(elm) < 0)
                max = elm;

        return max;

2. Class Fruit
public class Fruit implements Comparable<Fruit> {
    private String name;
    private int size;

    public Fruit(String name, int size) { = name;
        this.size = size;
    public int compareTo(Fruit that) {
        if (size < that.size)
            return -1;
        else if (size == that.size)
            return 0;
            return 1;

3. class Apple extending Fruit
public class Apple extends Fruit {
    public Apple(int size) {
    super("Apple", size);

Now the question is this:
public class Main
    public static void main(String[] args) {        
        Apple a1 = new Apple(10);
        Apple a2 = new Apple(34);
        List<Apple> apples = Arrays.<Apple>asList(a1, a2);

according to the Collection.max() function I should write
public static <T extends Comparable<? super T>> T max(Collection<? extends T> coll)

Because class Apple does not implement Comparable. But the one I have wrote is working fine without any problems.
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