可比较泛型的局部变量

Question

I'm trying to implement sorting for a generic list of Comparable objects. The problem is that I can't define a local variable for such lists and it leads to code duplicates.

Basically I need a variable that will maintain a returned value from a method with signature
<T extends Comparable<T>> List<Item<T>> getItems(int itemType, Class<T> cl) .

Here is the code https://ideone.com/mw3K26 . The goal is to avoid code duplicates on lines 25, 26 and 29, 30.

Is it even possible?

Answer 1

Put assosiations itemType -> Class to Map and use it instead if-else.

private static final Map<Integer, Class<? extends Comparable>> types = new HashMap<>();
static {
    types.put(1, Long.class);
    types.put(2, Date.class);
}

public List<Long> getSortedIds(int itemType) {
    Class<? extends Comparable> clz = types.get(itemType);
    if (clz != null) {
        List<Item> items = (List<Item>)getItems(itemType, clz);
        Collections.sort(items);
        return items.stream().map(it -> it.id).collect(Collectors.toList());
    }
    //...
    return null;
}