Inheritance and Polymorphism - General Questions

What is the output of the following program?

public class Main {
    public static void main(String[] args) {
        A a = new B();
        System.out.println(a.f());
    }
}
class A { String f() { return "A"; } }
class B extends A { String f() { return "B"; } }

What is the output of the following program?

public class Main {
    public static void main(String[] args) {
        new C();
        System.out.println();
    }
}
class A { A() { System.out.print("A"); } }
class B extends A { B() { System.out.print("B"); } }
class C extends B { C() { System.out.print("C"); } }

What is the output of the following program?

class A { A() { System.out.print("A"); } }
class B extends A { B() { System.out.print("B"); } }
class Main { public static void main(String[] args) { new B(); } }

Can an overriding method reduce visibility (e.g. public → private)?

What is the output of the following program?

public class Main {
    public static void main(String[] args) {
        A a = new B();
        System.out.println(a.x);
    }
}
class A { int x = 1; }
class B extends A { int x = 2; }