Java Generics Hell

java-generics-hell

import java.util.Comparator;

public class GenericsHell {
    public static void compareSomeNumbers(Comparator<Integer> numberComparison) {
        // ... elided ...
    }

    public static <T> Comparator<T> arbitraryOrder() {
        return new Comparator<T>() {
            @Override
            public int compare(T o1, T o2) {
                return 0;
            }
        };
    }

    public static void assignToVariable() {
        Comparator<Integer> comparator = arbitraryOrder();
        compareSomeNumbers(comparator);
    }

    public static void assignToParameter() {
        compareSomeNumbers(arbitraryOrder()); // Why does this not compile?
    }
}

Not fixed in Java 7

http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6293352

Note: although closed as not a defect, the comment says that it is only not being considered a defect because it's too difficult to change the compiler code to implement it.