if the following Java code were to appear in a control program that used the classes A,B and C what would be the outputs

Question

class A implements Once {

public void one () {
System.out.println("A.1") ;}

public void two () {
one();
System.out.println("A.2") ;}
public void sayItOnce () {
System.out.println("I'll say it once") ;}
}

class B extends A implements Once, Twice {

public void one (int x) {
System.out.println("B.1" + x) ;}

public void two () {
System.out.println("B.2") ;}

public void sayItTwice () {
System.out.println("\"I'll say it Twice") ;}
}

class C extends A {

public void one() {
System.out.println("C.1") ;}
}

interface Once {
void sayItOnce ();

}
interface Twice {
void sayItTwice ();
}

class control1{

//(i)
A a0 = new B ();
a0.two();

//(ii)
B b1 = new B()
b1.one(4);
b1.one();

//(iii)
Once r1 = new B();
r1.sayItOnce();

//(iv)
Twice b2 = new Twice();
b2.sayItTwice();

//(v)
C c = new A();
c.two();

//(vi)
A a2 = new B();
a2.sayItTwice();

//(vii)
A a3 = new C();
a3.two();
}

Answer 1

can someone explain this code and the output it would give?

this is the exact code given in a previous exam question.
I cant get it to compile to test the output

Answer 2

Got the code to work.

class A implements Once {

public void one () {
System.out.println("A.1") ;}

public void two () {
one();
System.out.println("A.2") ;}
public void sayItOnce () {
System.out.println("I'll say it once") ;}
}

class B extends A implements Once, Twice {

public void one (int x) {
System.out.println("B.1" + x) ;}

public void two () {
System.out.println("B.2") ;}

public void sayItTwice () {
System.out.println("\"I'll say it Twice") ;}
}

class C extends A {

public void one() {
System.out.println("C.1") ;}
}

interface Once {
void sayItOnce ();

}
interface Twice {
void sayItTwice ();
}

class Control{

public static void main (String args[]) {
System.out.println("\n(i)");
A a0 = new B ();
a0.two();

System.out.println("\n(ii)");
B b1 = new B();
b1.one(4);
b1.one();

System.out.println("\n(iii)");
Once r1 = new B();
r1.sayItOnce();

System.out.println("\n \t(iv) ERROR");
//Twice b2 = new Twice();
//b2.sayItTwice();
System.out.println("error: Twice is abstract; cannot be instantiated");

System.out.println("\n \t(v) ERROR");
System.out.println(" C c = new A()");
System.out.println(" c.two()");
System.out.println(" incompatible types: A cannot be converted to C");

System.out.println("\n \t(vi) ERROR");
A a2 = new B();
//a2.sayItTwice();
System.out.println("Compiliation error");
System.out.println("there is no sayItTwice() method in Class A");

System.out.println("\n(vii)");
A a3 = new C();
a3.two();
}
}