Java Generics and Infinity (Comparable)

Question

With the type Integer you can do this:

int lowest = Integer.MIN_VALUE;

What can I do if I use generics?

K lowest = <...>;

I need this in order to implement something similar to a PriorityQueue. I have access to a node I want to remove from the queue, but it is not the min.

1. I need to make it the min by decreasing the key of that node,
2. And then remove the min.

I am stuck on the first step. The only thing I can do is set the key of the node to the current min. Not sure it is enough.

Answer 1

There is no generic form of MIN_VALUE or MAX_VALUE for all Comparable types.

Think about a Time class that implements comparable. There is no MAX_VALUE for Time even though it is Comparable.

Answer 2

I am trying to imagine what scenario would require such behavior. This is the best I can come up with...

WARNING: This code is dangerous. Please be merciful to me for posting such an abomination. It is only a proof of concept.

public class Lowest<K> implements Comparable<K> {
    public int compareTo(K other) {
        return -1;
    }
}

And then...

public class Test {
    public <K extends Comparable<K>> K findMaximum(List<K> values) throws Exception {
        K lowest = (K) new Lowest<K>(); /// XXX DANGER! Losing compile-time safety!!!

        K maximum = lowest;
        for (K value : values) {
            if (maximum.compareTo(value) < 0) {
                maximum = value;
            }
        }

        if (maximum == lowest) {
            throw new Exception("Could not find a maximum value");
        } else {
            return maximum;
        }
    }
}