泛型和传递数组作为参数的麻烦

Question

So I am having trouble with a project I am working on. The project sounds very simple, I was able to complete 2/3 of it. I have to add 3 generic methods to my class MyGenerics. The method are:

a. mymin, where an array (of indeterminate type) is passed in as a parameter and the minimum element is returned.

b. max2, which accepts an array (of indeterminate type) is passed in as a parameter and the largest two elements are returned.

c. median, which accepts an array (of indeterminate type) is passed in as a parameter and the median is returned.

I was able to complete a and c very easily. my issue is with b. I cannot figure out how to return the max, as well as the second largest value. My initial idea was to get the initial max value in the array, then remove it and get the max again, so that the "new" max would then be the second highest. Here is my code:

public class MyGenerics {

public static void main(String[] args) {
    Integer intArray[] = { 13, 25, 46, 65, 12, 23};
    Double doubleArray[] = {1.2, 3.4, 1.1, 0.1, 5.6};
    String stringArray[] = {"H", "E", "L", "L", "O"};

    System.out.println("The smallest number is: " + myMin(doubleArray));
    System.out.println("The median is: " + median(doubleArray));
    System.out.println("The median is: " + median(stringArray));
    System.out.println("The max is: " + max2(intArray));
}

 public static <E extends Comparable<E>> E myMin(E... elements) {

        E min = elements[0];
        for (E element : elements) {
            if (element.compareTo(min) < 0) {
                min = element;
            }
        }
        return min;
    }

 public static <E extends Comparable<E>> E max2(E... elements) {

      E max = elements[0];
        for (E element : elements) {
            if (element.compareTo(max) > 0) {
                max = element;
            }
        }
        return max; <-- so obviously this returns the max value of the elements
                        how can i return the max, as well as the second largest value?
    }



public static <E extends Comparable<E>> E median(E... elements) {
 Arrays.sort(elements);

 E median = elements[elements.length/2];

 return median;


 }
}

Hopefully this makes as much sense as possible. again, what can I do to now only get the max value to print, but also the second largest value. Thank you.

Answer 1

Arrays are low-level constructs; generally, use collection APIs instead.

I'm not sure if your confusion is about making a 2-length array, or if it's about finding the top 2 elements.

If it's the former:

Making new arrays of generic types is normally impossible (because of erasure), but in this case you can crib off of your existing array:

E[] out = (E[]) java.lang.reflect.Array.newInstance(elements.getClass().getComponentType(), 2);

yup, ugly, weird, convoluted, and will generate some generics warnings you'll have to ignore.

As far as the part about tracking the 2 biggest goes, You can use the same trick as you've used so far, just, with more comparisons (compare any number to both the max and the second-to-max).

Another option is to sort the array and just return the last 2 elements. There's Arrays.sort which can be helpful.