Question

I created small utility which helps me sort my map by values (based on one of the StackOverflow answers to give credit):

public static <K, V extends Comparable> Map<K, V> sortMapByValues(Map<K, V> original) {
    final ValueComparator<K, V> comparator = new ValueComparator<K, V>(original);
    final Map<K, V> sorted = new TreeMap<K, V>(comparator);
    sorted.putAll(original);

    return sorted;
}

And the ValueComparator:

static class ValueComparator<K, V extends Comparable<V>> implements Comparator<K> {
    private final Map<K, V> base;

    public ValueComparator(Map<K, V> base) {
        this.base = base;
    }

    public int compare(K a, K b) {
        return base.get(b).compareTo(base.get(a));
    }
}

Now this works pretty well when in my IntelliJ 10 IDE, the code runs and do what I expect.

But if I try to build the project by maven from command line I get following error:

type parameter V is not within its bound

The error is said to be on the first line of the sortMapByValues() method

I am using JDK 6 in my IDE and my maven compiler plugin is set to 1.6 as well.

Any tips appreciated

Answer 1

I guess it is because of:

V extends Comparable (in sortMapByValues) and V extends Comparable<V> in class ValueComparator.

Change the first also to V extends Comparable<V>