How do I write generic Java method and compare two variables of the generic type inside the method?

Question

I have written the following code:

private static <T> T getMax(T[] array) {
        if(array.length == 0) {
            return null;
        }

        T max = array[0];
        for (int i = 1; i < array.length; i++) {
            if (array[i] > max)
                max = array[i];
        }
        return max;
    }

The problem is in this line: if(array[i] > max).

I understand that Java can't understand the > operator in case of unknown/arbitrary classes.

At the same time, I don't want to write different methods for the objects of the classes that I know I'll be sending.

Is there a workaround?

Answer 1

You need to change T to T extends Comparable<T> and use the compareTo method. That is:

• private static <T extends Comparable<T>> T getMax(T[] array), and
• if (array[i].compareTo(max) > 0) { ... }

But note that you can use

maxElement = Collections.max(Arrays.asList(array));

Answer 2

Yes, there is a workaround, by adding a Comparable upper bound to T.

Because the < operator doesn't work on objects, you must use the equivalent functionality, which is the compareTo method in the Comparable interface.

Ensure that the type T is Comparable by providing an upper bound.

private static <T extends Comparable<T>> T getMax(T[] array)

Then, in place of the > operator, call compareTo:

if(array[i].compareTo(max) > 0)