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Inheritance Unit Test

Last updated almost 2 years ago

13 questions

5

5

5

5

5

5

5

5

5

5

5

5

40

Question 1

1.

What is the output by the code below?
public class J
{
private int x, y;
public J() {
x = y = 3;
}
public void fun() {
x = y = 6;
}
public int back() {
return 1;
}
public String toString() {
return x + " " + y;
}
}
public class K extends J {
public void fun() {
out.println(back());
}
public String toString() {
return "class K " + super.toString();
}
}
//test code in a client program
J runner = new K();
out.println(runner);

class K 6 6

class K 6 3

class K 3 3

class K 1 3

class K 3 6

Question 2

2.

Which of the following lines would correctly fill /* blank / to pass x to the appropriate parent constructor?
public class P
{
private int one;
public P(){ one=0; }
public P(int num){
one=num;
}
}
public class Q extends P
{
public Q() { }
public Q(int x){
/ blank */
}
}

this(x);

parent(x);

super(x);

that(x);

super();

Question 3

3.

What is output by the code below?

Object c = new String("Hello");
String d = new String("Hello");
System.out.println(c.equals(d));

null

hello

c=d

true

false

Question 4

4.

What is the output of line 2?
public class X{
public void one(){
System.out.print("Xone");
}
public void two(){
System.out.print("Xtwo");
}
}
public class Y extends X{
public void one(){
System.out.print("Yone");
}
public void two(){
System.out.print("Ytwo");
}
public void testIt(){
one();
super.one();
two();
super.two();
}
}
//code in the main of another class
Y code = new Y();
code.one(); //line 1
code.testIt(); //line 2

YoneXoneYtwoXtwo

XoneXoneYoneYone

XoneXtwoYoneYtwo

XoneYoneXtwoYtwo

YoneXtwoYtwoXtwo

Question 5

5.

What is output by the code below?
public class Cat {
private int x, y;
public Cat() {
x=y=5;
}
public void fun() {
x=7;
}
public double go() {
return x;
}
public void back() {
fun();
}
public String toString() {
return x + " " + y;
}
}
public class Lion extends Cat {
private int x;
public Lion() {
x=9;
}
public void fun() {
x=3;
}
public double go() {
return x;
}
public void back() {
super.back();
}
public String toString() {
return super.toString() + " " + x;
}
}
//code in a client program
Cat fred = new Lion();
fred.fun();
System.out.println(fred.go());

7.0

3.0

9.0

5.0

1.0

Question 6

6.

What is output by the code below?
public class Whale
{
private int x, y;
public static int c;
public Whale() {
c++;
}
public void fun() {
x = 6;
}
public int back() {
return 1;
}
public String toString() {
return x + " " + y + " " + c;
}
}
public class Beluga extends Whale
{
public void fun() {
System.out.println(back());
}
public int back() {
return 2;
}
public String toString() {
return "class Beluga " + super.toString();
}
}
//code in the main of another class
Whale flipper = new Beluga();
flipper = new Whale();
flipper = new Beluga();
flipper = new Whale();
flipper.fun();
System.out.println(flipper);

0 0 4

6 0 3

6 0 4

6 0 6

6 0 2

Question 7

7.

Consider the following code.
public interface Box
{
int mystery(int num);
}
public abstract class Stuff
{
private int x;
public Stuff()
{
x = 5;
}
public Stuff(int newX)
{
x = newX;
}
public abstract void doStuff();
public abstract int doubleIt();
}
public class LotsOfStuff extends Stuff implements Box
{
/* implementation not shown */
}
What methods should the class LotsOfStuff implement?

doStuff()
doubleIt()

mystery(int num)
doStuff()
doubleIt()

mystery(int num)
doStuff()

mystery(int num)

mystery(int num)
Stuff()
Stuff(int newX)
doStuff()
doubleIt()

Question 8

8.

Which methods must be implemented in any class that inherits from the class Stuff?
public abstract class Stuff
{
private int x;
public Stuff()
{
x = 5;
}
public Stuff(int newX)
{
x = newX;
}
public abstract void doStuff();
public abstract int doubleIt();
}

Stuff()
Stuff(int newX)
doStuff()
doubleIt()

Stuff()
doStuff()
doubleIt()

doStuff()

doStuff()
doubleIt()

None need to be implemented

Question 9

9.

What is the number of methods a class extending abstract class Aplus should implement?
public abstract class Aplus
{
public Aplus()
{
}
public abstract String destroy();
public String toString()
{
return "--";
}
}

0

1

2

3

4

Question 10

10.

public class X Y ___ A, B, C

a. extends  implements

b. extends extends

c. implements extends

d. implements implements

e. A and B only

Question 11

11.

All variables located inside of an interface are automatically set with what access?

a. public

b. private

c. protected

d. A and B only

e. A, B, and C

Question 12

12.

Which of the following is the correct way to write the interface Screen?
I.
public interface Screen
{
void updateDisplay()
{
}
int getTime();
}

II.
public interface Screen
{
public Screen()
{
}
void updateDisplay();
int getTime();
}

III.
public interface Screen
{
void updateDisplay();
int getTime();
}

III only

II only

I only

I and III only

II and II only

Question 13

13.

Directions :: Extend class Drink to make a Tea class. Tea must have a constructor. Tea must have an instance variable for type of tea. Tea must have an instance variable for the amount left. Tea must have a Boolean method that determines if the Tea is empty. Tea must have a method that removes 1 from amount left when a drink is taken.