Why does sort take an Object array?

Question

I just stumbled upon the following overloads of sort in java.util.Arrays:

public static void sort(Object[] a)

public static <T> void sort(T[] a, Comparator<? super T> c)

Why is the first overload not generic, but the second one is? Why does the first overload take an Object[] instead of a Comparable[]? The documentation even states:

All elements in the array must implement the Comparable interface.

So what's the point of not verifying that constraint with Java's static type system?

Answer 1

The first method could be better if it were generic, but it would break compatibility with pre 1.5 code:

static <T extends Comparable<T>> void sort(T[] a) {
    ...
}

static void main(String[] args) {
   Object[] a = {"1", "2"};
   sort(a); <- compile time error, need explicit cast sort((Comparable[])a);
}

While the second one compiles with 1.4 code with warning only

public static <T> void sort(T[] a, Comparator<? super T> c) {
    ...
}

public static void main(String[] args) throws Exception {
    Object[] a = { "1", "2" };
    sort(a, new Comparator() {   <-- warning 
        @Override
        public int compare(Object o1, Object o2) {
            return 0;
        }
    });
}