Adding generics to ArrayUtils.toMap

Question

there is an open-source util library from Apache, where I found a method to convert an array into a map:

public static Map toMap(Object[] array) {
    if (array == null) {
        return null;
    }
    final Map map = new HashMap((int) (array.length * 1.5));
    for (int i = 0; i < array.length; i++) {
        Object object = array[i];
        if (object instanceof Map.Entry) {
            Map.Entry entry = (Map.Entry) object;
            map.put(entry.getKey(), entry.getValue());
        } else if (object instanceof Object[]) {
            Object[] entry = (Object[]) object;
            if (entry.length < 2) {
                throw new IllegalArgumentException("Array element " + i + ", '"
                    + object
                    + "', has a length less than 2");
            }
            map.put(entry[0], entry[1]);
        } else {
            throw new IllegalArgumentException("Array element " + i + ", '"
                    + object
                    + "', is neither of type Map.Entry nor an Array");
        }
    }
    return map;
}

Because I don't like warnings, I tried to add generics. But I don't know how to transfer the datatype from the input array to the output map.

Is it possible?

Answer 1

It is only possible if you create two separate methods: one that deals with Map.Entry elements, and another that deals with "array" elements (e.g. {"RED", "#FF0000"}). Here is the code:

public static <K, V> Map<K, V> toMap(Map.Entry<K, V>[] array) {
    if (array == null) {
        return null;
    }

    final Map<K, V> map = new HashMap<K, V>((int) (array.length * 1.5));
    for (int i = 0; i < array.length; i++) {
        Map.Entry<K, V> entry = array[i];
        map.put(entry.getKey(), entry.getValue());
    }
    return map;
}

@SuppressWarnings("unchecked")
public static <K, V> Map<K, V> toMap(Object[][] array) {
    if (array == null) {
        return null;
    }

    final Map<K, V> map = new HashMap<K, V>((int) (array.length * 1.5));
    for (int i = 0; i < array.length; i++) {
        Object[] entry = array[i];
        map.put((K) entry[0], (V) entry[1]);
    }
    return map;
}

Even though some some of the code is duplicated, it is arguably more elegant. I'm afraid there is no better solution for the second method; array can only be reified at runtime. Thus, "unchecked" casts have to be made.