Question

Can I find out from which class a given method’s implementation is inherited? e.g. in the current object, which toString() implementation is used, from Object class, or some other parent class?

Answer 1

Try Method.getDeclaringClass() (link to 1.5 API)

public Class<?> getDeclaringClass()

Returns the Class object representing the class or interface that declares the method represented by this Method object.

Specified by:
getDeclaringClass in interface Member

Returns:
an object representing the declaring class of the underlying member

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Note that you cannot know if the implementing class only calls the super:

public String toString() {
    return super.toString();
}

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To determine the class from which the method is inherited you would need to:

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

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Example:

public static void main(String[] args) throws Exception {
  System.out.println(String.class.getMethod("toString").getDeclaringClass());
  System.out.println(ArrayList.class.getMethod("toString").getDeclaringClass());
  System.out.println(Area.class.getMethod("toString").getDeclaringClass());
}

Outputs:

class java.lang.String
class java.util.AbstractCollection
class java.lang.Object

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I noticed from the question that you wanted to get super class that overrides the method if available. Here is a demo:

import java.lang.reflect.Method;

public class ReflectionCode {
    public static void main(String[] args) throws SecurityException, NoSuchMethodException, ClassNotFoundException {
        System.out.println(getInheritedClass(Parent.class.getName(),"overRiddenMethod"));
        System.out.println(getInheritedClass(Child.class.getName(),"overRiddenMethod"));
    }

    public static String getInheritedClass(String className, String method){
        Class clazz;
        try {
            clazz = Class.forName(className);

            if(clazz.getSuperclass() != null && clazz.getSuperclass().getMethod(method) != null)
            {
                return clazz.getSuperclass().getName();
            }
        }catch(Exception e){

        }
        return "none";
    }
}

class Parent  {

    public void overRiddenMethod(){

    }
}

class Child extends Parent {

    public void overRiddenMethod() {

    }
}