OCA Chuong 3

Question 1: Given:

public abstract interface Frobnicate {

public void twiddle(String s);

}

• A. public abstract class Frob implements Frobnicate {

  public abstract void twiddle(String s){};

  }

• B. public abstract class Frob implements Frobnicate {

  }

• C. public class Frob extend Frobnicate {

  public void twiddle(Integer i){};

  }

• D. public class Frob implements Frobnicate{

  public void twiddle(Integer i){};

  }

• E. public class Frob implements Frobnicate {

  public void twiddle(String i){}

  public void twiddle(Integer s){}

  }

Question 2: Given:

class Top {

public Top(String s){

System.out.print("B");

}

}

public class Button2 extend Top {

public Button2(String s){

System.out.print("D");}

public static void main(String[] args){

new Button2("C");

System.out.println (" ")

}

}

• A. BD

• B. DB

• C. BDC

• D. DBC

• E. Complilation fails

Question 3: Given:

class Clidder {

private final void flipper() {

System.out.println("Clidder");}

}

public class Clidlet extend Clidder {

public final void flipper(){

System.out.println("Clidlet");

}

public static void main(Sring[] args) {

new Clidlet().flipper();

}

}

• A. Clidlet

• B. Clidder

• C. Clidder

  Clidlet

• D. Clidlet

  Clidder

• E. Compilation fails

Using the fragments bellow, complete the following code so it compiles. Note that you may not have to fill in all of the slots

Code:

class AgedP {

_____ ____ ____ ____ ____

public AgedP(int x) {

---- ---- ---- ---- ---- ----

}

}

public class Kinder extends AgedP {

____ ____ ____ ____ ____ ____

public Kinder (int x) {

____ ____ ____ ____ ____ ();

}

}

Fragments: Use the following fragments zero or more times:

AgedP super this ( { ) } ;

Question 5: Given:

class Bird {

{ System.out.print("b1");}

public Bird(){System.out.print("b2");}

}

class Raptor extends Bird {

static { System.out.print("r1");}

public Raptor(){System.out.print("r2");}

{System.out.print("r3");}

static {System.out.print("r4");}

}

class Haw extend Raptor {

public static void main (String [] args) {

System.out.print("pre");

new Hawk();

System.out.println("hawk");}

}

• A. pre b1 b2 r3 r2 hawk

• B. pre b2 b1 r2 r3 hawk

• C. pre b2 b1 r2 r3 hawk r1 r4

• D. r1 r4 pre b2 b1 r2 r3 hawk

• E. Compilation fails

Question 6: Given the following:

1. class X {void do1(){}}

2. class Y extends X {void do2() {}}

3. class Chrome {

4. public static void main (String[] args){

5. X x1 = new X();

6. X x2 = new Y();

7. Y y1 = new Y();

8/ // insert code here

9. }}

Which of the following, inserted at line 8, will compile? (choose all that apply)

• A. x2.do2();

• B. (Y)x2.do2();

• C. ((Y)x2).do2();

• D. None of the above statements will compile

Question 7: Given:

public class Locomotive {

Locomotive(){ main("hi");}

public static void main(String[] args){

System.out.print("2");

}

public static void main(String args){

System.out.print("3"+args);

}

}

• A. 2 will be included in the output

• B. 3 will be included in the output

• C. hi will be included in the output

• D. Compilation fails

• E. An exception is thrown at runtime

Question 8: Given:

3. class Dog {

4. public void bark(){System.out.printl("woof");}

5. }

6. class Hound extends Dog {

7. public void sniff(){System.out.print("sniff");}

8. public void bark(){System.out.print ("howl");}

9. }

10. public class DogShow {

11. public static void main (String[] args) {new DogShow().go();}

12. void go(){

13. new Hound().bark();

14. ((Dog) new Hound()).bark();

15. ((Dog) new Hound()).sniff();

16. }

17. }

• A. howl howl sniff

• B. howl woof sniff

• C. Compilation fails with an error at line 14

• D. Compilation fails with an error at line 15

• E. howl woof followed by an exception

Question 9: Given:

3. public class Redwood extends Tree {

4. public static void main (String[] args){

5. new Redwood().go();

6. }

7. void go() {

8. go2(new Tree(), new Redwood());

9. go2((Redwood) new Tree(), new Redwood());

10. }

11. void go2(Tree t1, Redwood r1){

12. Redwood r2 = (Redwood) t1;

13. Tree t2 = (Tree) r1;

14 . }

15. }

16. class Tree {}

• A. An exception is thrown at runtime

• B. The code compiles and runs with no output

• C. Compilation fails with an error at line 8

• D. Compilation fails with an error at line 9

• E. Compilation fails with an error at line 12

Question 10: Given:

3. public class Tenor extends Singer {

4. public static String sing() {return "fa";}

5. public static void main(String[] args) {

6. Tenor t = new Tenor();

7. Singer s = new Tenor();

8. System.out.println(t.sing() + " " + s.sing());

9. }

10. }

• A. fa fa

• B. fa la

• C. la la

• D. Compilation fails

• E. An exception is thrown at runtime