Java getMethod: resolve an overload by its exact parameter types

Last updated: 7 Oct 20265 min read

tutorial

Class.getMethod selects a public method by name and exact parameter-type array. It does not search for the overload that would be chosen by a normal source-code call.

Operational contract

The lookup specifies long and int primitives, then invokes a single rate method. A Long.class parameter is not long.class. Method.invoke may box arguments during invocation, but that conversion does not change the method selected during lookup. If the requested signature is absent, NoSuchMethodException signals a contract mismatch; selecting the first method with the right name can silently call a different overload. The sample checks the result type before unboxing it.

Failure case

A pricing plugin adds rate(Long, int) beside rate(long, int). Looking up Long.class when the integration contract calls for long.class fails instead of silently choosing a different policy.

Java code

import java.lang.reflect.Method;
import java.util.Objects;

public class DepotRateLookup {
    public static long cents(Object rateTable, long depotId, int parcelCount)
            throws ReflectiveOperationException {
        Objects.requireNonNull(rateTable);
        Method rate = rateTable.getClass().getMethod("rate", long.class, int.class);
        Object result = rate.invoke(rateTable, depotId, parcelCount);
        if (!(result instanceof Long cents) || cents < 0)
            throw new IllegalStateException("Rate must be nonnegative long cents");
        return cents;
    }
}

Performance and ownership cost

Signature lookup and invocation add reflective overhead and O(1) application storage. For a fixed plugin API, validate and cache the selected Method at registration instead of scanning overloads on each request.

Common Mistakes

Do not substitute Long.class for long.class in an exact lookup.
Do not pick an overload by name alone.
Do not assume a reflected result has the required type or valid business range.

Connected lessons

java

reflective invocation

reflection-exact-overload-lookup