Review Questions

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6.25

What will be the result of attempting to compile and run the following program?

public class Polymorphism {
    public static void main(String[] args) {
        A ref1 = new C();
        B ref2 = (B) ref1;
        System.out.println(ref2.f());
    }
}

class A           { int f() { return 0; } }
class B extends A { int f() { return 1; } }
class C extends B { int f() { return 2; } }

Select the one correct answer.

  1. The program will fail to compile.

  2. The program will compile without error, but will throw a ClassCastException when run.

  3. The program will compile without error and print 0 when run.

  4. The program will compile without error and print 1 when run.

  5. The program will compile without error and print 2 when run.

6.26

What will be the result of attempting to compile and run the following program?

public class Polymorphism2 {
    public static void main(String[] args) {
        A ref1 = new C();
        B ref2 = (B) ref1;
        System.out.println(ref2.g());
    }
}

class A {
    private int f() { return 0; }
    public int g() { return 3; }
}
class B extends A {
    private int f() { return 1; }
    public int g() { return f(); }
}
class C extends B {
    public int f() { return 2; }
}

Select the one correct answer.

  1. The program will fail to compile.

  2. The program will compile without error and print 0 when run.

  3. The program will compile without error and print 1 when run.

  4. The program will compile without error and print 2 when run.

  5. The program will compile without error and print 3 when run.



     
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