java.lang.ClassCastException：排序时无法将java.lang.Short强制转换为java.lang.Integer

Question

How to sort hashmap by value if the values are Short type HashMap<Long, Short>() ?

when I use generic sorting like

public static <K extends Comparable<K>, V extends Comparable<V>> Map<K, V> sortByValues(final Map<K, V> map) {
    Comparator<K> valueComparator =  new Comparator<K>() {
        public int compare(K k1, K k2) {
            int compare = map.get(k1).compareTo(map.get(k2));
            return compare != 0 ? compare : k1.compareTo(k2);
        }
    };
    Map<K, V> sortedByValues = new TreeMap<K, V>(valueComparator);
    sortedByValues.putAll(map);
    return sortedByValues;
}

I get this error:

java.lang.ClassCastException: java.lang.Short cannot be cast to java.lang.Integer

Answer 1

There are no explicit typecasts anywhere in this code.

Therefore, I conclude that the ClassCastException is caused by the implicit typecasts that the compiler inserts when you assign a value returned by some generic method to a variable with a specific type.

Furthermore, since the implicit typecasts only fail in circumstances where you have / someone has choosen to ignore or suppress Java compiler warnings about unsafe conversions, etcetera, I conclude that

• this must have happened, and
• it is the cause of your problem.

In short, the cause of problem is not in the code you have included in the question. It is somewhere else ...

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In future, be sure to include:

• Sufficient context to allow people to see how your code is being used. Ideally an MCVE.
• The complete stacktrace for the exceptions.