Upcasting java RTTI

public class A {
    public static void main(String[] args) {
        B b = new B();
        A a = new B();
        a.f();
        A aaa = (A) b;
        aaa.f();
    }
    public void f() {
        System.out.println("I'm A");
    }
}
class B extends A {
    public void f() {
        System.out.println("I'm B");
    }
}

i ran this code, and get the result as below:

I'm B

I'm B

both a and aaa have a instance of B, so i think the result is reasonable.

however, i ran another code, like this:

public class Atest {
    public static void main(String[] args) {
        Atest a1 = new Atest();
        Object a2 = new Atest();
        System.out.println(a1.equals(a2));
        System.out.println(a2.equals(a1));
        System.out.println(a1.equals(new C()));
        System.out.println(a2.equals(new C()));
    }

    public boolean equals(Object o) {
        System.out.println("equals(Object o) is called!");
        return true;
    }
    public boolean equals(Atest a) {
        return true;
    }
    public boolean equals(C c) {
        System.out.println("equals(C c) is called!");
        return true;
    }
}
class C {

}

and, i got the result

equals(Object o) is called!

true

equals(Object o) is called!

true

equals(C c) is called!

true

equals(Object o) is called!

true

i am confused that a2.equals(new C()) call the function public boolean equals(Object o)

a2 is an instance of Atest, i think a2.equals(new C()) should call the function public boolean equals(C c).

anybody can help me? really thanks!