Repeated Reflection in Loop

Rule details

Rule ID	repeated-reflection-in-loop
Severity	INFO — worth knowing, may not matter at your scale
Confidence	MEDIUM — likely correct, some context-dependent
Category	Loop amplifiers
Complexity	O(n·reflection) → O(n)

Description

Detects Java/Kotlin reflection calls inside loops. Reflection methods like getDeclaredMethods(), getDeclaredFields(), and getAnnotations() are 10-100x slower than direct access. They also allocate new arrays on each call, adding GC pressure. Results should be cached outside the loop.

This rule only flags the expensive reflection methods that perform class scanning or array allocation. Cheap accessors like getModifiers(), getName(), and getReturnType() are excluded.

Typical

Java

for (Class<?> orderType : orderTypes) {
    Method[] methods = orderType.getDeclaredMethods();   // Array allocated every iteration
    for (Method m : methods) {
        if (m.isAnnotationPresent(OrderProcessor.class)) {
            processorMethods.add(m);
        }
    }
}

After

Java

Map<Class<?>, Method[]> methodCache = new HashMap<>();
for (Class<?> orderType : orderTypes) {
    Method[] methods = methodCache.computeIfAbsent(
        orderType, Class::getDeclaredMethods);           // Cached per class
    for (Method m : methods) {
        if (m.isAnnotationPresent(OrderProcessor.class)) {
            processorMethods.add(m);
        }
    }
}

Suggestion

Cache the reflection result in a local variable or Map outside the loop

Detected Methods

getDeclaredMethods, getDeclaredFields, getDeclaredConstructors, getDeclaredAnnotations, getMethods, getFields, getConstructors, getAnnotations, getAnnotationsByType, getDeclaredAnnotationsByType, getGenericInterfaces, getInterfaces, getDeclaredClasses, getClasses, getParameterTypes, getGenericParameterTypes, getExceptionTypes