apache/flink · error · RuntimeException

Could not initialize comparator {}

Error message

Could not initialize comparator {}

What it means

SqlTimeTypeInfo.instantiateComparator reflectively builds the SQL-time comparator (Date, Time, Timestamp) via comparatorClass.getConstructor(boolean.class).newInstance(ascending). If the comparator class lacks the public boolean constructor or instantiation fails, a RuntimeException names the comparator class. This is the same reflection contract as BasicTypeInfo/LocalTimeTypeInfo, applied to java.sql time types.

Source

Thrown at flink-core/src/main/java/org/apache/flink/api/common/typeinfo/SqlTimeTypeInfo.java:162

            return false;
        }
    }

    @Override
    public String toString() {
        return clazz.getSimpleName();
    }

    // --------------------------------------------------------------------------------------------

    private static <X> TypeComparator<X> instantiateComparator(
            Class<? extends TypeComparator<X>> comparatorClass, boolean ascendingOrder) {
        try {
            Constructor<? extends TypeComparator<X>> constructor =
                    comparatorClass.getConstructor(boolean.class);
            return constructor.newInstance(ascendingOrder);
        } catch (Exception e) {
            throw new RuntimeException(
                    "Could not initialize comparator " + comparatorClass.getName(), e);
        }
    }

    @SuppressWarnings("unchecked")
    public static <X> SqlTimeTypeInfo<X> getInfoFor(Class<X> type) {
        checkNotNull(type);

        if (type == Date.class) {
            return (SqlTimeTypeInfo<X>) DATE;
        } else if (type == Time.class) {
            return (SqlTimeTypeInfo<X>) TIME;
        } else if (type == Timestamp.class) {
            return (SqlTimeTypeInfo<X>) TIMESTAMP;
        }
        return null;
    }
}

View on GitHub (pinned to 2f3c205e92)

Solutions

1. Ensure the comparator class for SQL-time types exposes a public constructor accepting a single boolean.
2. Avoid overriding SqlTimeTypeInfo/comparator classes; rely on the built-in implementations.
3. On restricted JDKs, add the appropriate --add-opens for the comparator package.

Example fix

// before: custom comparator missing boolean constructor

// after: use built-in SqlTimeTypeInfo for Date/Time/Timestamp;
// or ensure: public MyComparator(boolean ascending) { ... }

try {
    comparatorClass.getConstructor(boolean.class);
} catch (NoSuchMethodException e) {
    throw new IllegalStateException(
        comparatorClass + " must have a public (boolean) constructor", e);
}

static boolean hasBooleanCtor(Class<? extends TypeComparator<?>> c) {
    try { c.getConstructor(boolean.class); return true; }
    catch (NoSuchMethodException e) { return false; }
}

try {
    return SqlTimeTypeInfo.instantiateComparator(clazz, asc);
} catch (RuntimeException e) {
    throw new IllegalStateException(
        "SqlTime comparator " + clazz + " misconfigured", e);
}

When it happens

Trigger: A custom SqlTimeTypeInfo with a comparatorClass missing the (boolean) constructor; reflective access blocked by JDK settings; comparator class corrupted or abstract in a forked build.

Common situations: Forking Flink and altering the SQL-time comparators; strict module path blocking reflective construction; classpath corruption loading a partial comparator class; migrating between JDK versions that tighten reflection.

Related errors

• Could not initialize basic comparator {}
• Could not initialize comparator {}
• Could not initialize primitive {} array comparator.
• The type {} cannot be used as a key.
• SQL time type expected.

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/e6dbf220e50e1dd5. Report an issue: GitHub.