Finder idea to detect overloading pitfall

Hello,

this one is not easy to describe. I hope I make the point clear. If not 
please ask.

In principal it is a more general form of the 
http://findbugs.sourceforge.net/bugDescriptions.html#EQ_SELF_NO_OBJECT 
bug pattern.


If we have 2 classes class A and B where class A extends B and class A 
contains a method taking objects of class A as argument, an there is 
also a method that takes objects of class B (or any base type of A) as 
argument (overloaded) than the latter method should call instanceoff and 
delegate to the method taking objects of class A as argument if the 
passed object is instance off class A.


Example:

class B
{
}

class A
    extends B
{
    void foo(A a)
    {
        System.out.println("A");
    }

    void foo(B b)
    {
        // if this if is missing and the code is
        // different to foo(A) than FindBugs should
        // complain.
        if (b instanceof A)
        {
            foo((A) b);
        }
        System.out.println("B");
    }
}

Otherwise new A().foo((B) new A()) will behave strange and print out B. 
This is due to the fact that the linking of this calls is done during 
compiletime and not during runtime.



A common instance of this bug is a equals method that takes Object 
instances as argument:

void boolean equals (A a)
{
   ...
}

void boolean equals (Object obj)
{
    return false;
}


Got the point? Might be worth to write a FindBugs checker for this?


Regards,

Andreas.