Java: How to find if a method is overridden from base class? [duplicate]

Answer 1

I think the answers so far are assuming that you have a method and are trying to determine whether that method is overridden in a class.

However, the actual question asked was "Given an instance of B, how do I know if any derived classes have overridden method m() like B2?"

This is not possible to do using standard Java methodology, because Java does not load classes until they are referenced. For example, assume you have a URL classloader loading from a jar (or many jars) on the network. Java has no idea what classes are contained in those networked jar files, let alone whether they happen to override a particular method.

I think that I've seen utilities in Apache commons that will try to exhaustively search the hierarchy of classloaders to assemble a list of all available classes, but this sounds like a pretty bad idea to me. For one thing, it will trigger every single static initializer block for every class in the JVM.

There are some facilities like the Service Provider Interface to list class names in the jar's META-INF directory that implement a certain interface, maybe you should look at that route.

Answer 2

Improving the post by Pavel Savara, here's my version of the method that works for interfaces too:

public static boolean isMethodOverrriden(final Method myMethod) {
    Class<?> declaringClass = myMethod.getDeclaringClass();
    if (declaringClass.equals(Object.class)) {
        return false;
    }
    try {
        declaringClass.getSuperclass().getMethod(myMethod.getName(), myMethod.getParameterTypes());
        return true;
    } catch (NoSuchMethodException e) {
        for (Class<?> iface : declaringClass.getInterfaces()) {
            try {
                iface.getMethod(myMethod.getName(), myMethod.getParameterTypes());
                return true;
            } catch (NoSuchMethodException ignored) {

            }
        }
        return false;
    }
}

Answer 3

Java's reflection API has a Method class which has a method called getDeclaringClass(). That might work for what you need. Here is the API:

http://download.oracle.com/javase/6/docs/api/java/lang/reflect/Method.html#getDeclaringClass()

Answer 4

private static boolean isMethodImplemented(Object obj, String name)
{
    try
    {
        Class<? extends Object> clazz = obj.getClass();

        return clazz.getMethod(name).getDeclaringClass().equals(clazz);
    }
    catch (SecurityException e)
    {
        log.error("{}", e);
    }
    catch (NoSuchMethodException e)
    {
        log.error("{}", e);
    }

    return false;
}

Answer 5

This question helps demonstrate how to get the information of which class that method belongs to:

How to quickly determine if a method is overridden in Java

class.getMethod("myMethod").getDeclaringClass();

Answer 6

 public static boolean isMethodOverrriden(Method myMethod) {
     Class<?> declaringClass = myMethod.getDeclaringClass();
     if (declaringClass.equals(Object.class)) {
         return false;
     }
     try {
         declaringClass.getSuperclass().getMethod(myMethod.getName(), myMethod.getParameterTypes());
         return true;
     } catch (NoSuchMethodException e) {
         return false;
     }
 }