Missed Questions

Question 1

(double) (12/5) returns what?

Answer 1

2. The cast is performed too late

Question 2

Given that List doNothing(List list) simply returns “list” and is in class Test, what will happen in:

ArrayList nums = new ArrayList();
nums = Test.doNothing(nums)

Answer 2

doNothing returns a List, not an ArrayList, and you can’t assign a List object to an ArrayList variable. An ArrayList IS an List, however, so calling doNothing(ArrayList) IS valid.

Question 3

Which algorithm provides the most efficient way of finding the largest of 2000 elements stored in an array (not necessarily sorted)?

Answer 3

Selection Sort (terminated after the first five iterations). Selection Sort sorts by finding the largest elements in the list, etc…

Question 4

If an abstract class has no implemented constructors or methods, it is better to make it an _______

Answer 4

interface. All the advantages of inheritance are preserved, pus a class that implements the interface can potentially extend some other class

Question 5

Can an abstract class extend another abstract class?

Answer 5

YES

Question 6

Which of the following code segments correctly traverses a two-dimensional int array m, row by row?

Answer 6

A 2D array is implemented as a 1D array of its rows, where each row is a 1D array. Therefore, the elements of m have the type int[], not in.

Question 7

Can an abstract class implement an interface?

Answer 7

YES

Question 8

Can you declare an array of objects of an abstract class type, but not of an interface type?

Answer 8

NO

Question 9

A method cannot take a parameter of an interface type nor abstract class type

Answer 9

TRUE

Question 10

Object has neither ______ nor ______ method

Answer 10

substring, compareTo

Question 11

when removing elements from a list, be careful using a standard loop because:

Answer 11

list.remove(i) shifts the subscripts of the subsequent elements down by one, so only every other element is removed.

Question 12

In the GridWorld design, why is the Actor class not made abstract, with the act method abstract?

Answer 12

To be able to create Actor objects in GridWorld applications and explore their attributes and behavior. You cannot create an object of an abstract class.

Question 13

Suppose an array contains 127 different random values arranged in ascending order, and a most efficient searching algorithm is used to find a target value. How many elements of the array will be examined when the target equals arr[39]?

Answer 13

4. Binary search will look at arr[63], arr[31], arr[47], arr[39]

Question 14

Assuming a and b are Boolean variables, what is the same thing as the following:

!(!a || b) || (!a && b)

Answer 14

= (a && !b) || (!a && b). This evaluates to true if and only if a and b have different values.

Question 15

A project needs two related classes, X and Y. A programmer has decided to provide an abstract class A and derive both X and Y from A rather than implementing X and Y completely independently of each other. Which of the following is nOT a valid rationale for this design decision.

Answer 15

Being able to cast objects of type X into Y and vice-versa. This is NOT a good idea. They are both different animals, and both merely extend a super class, but NOT each other.

Question 16

If Game is an interface and Fun a class, then:

Game game = fun; is _____

Answer 16

an indication that Fun implements Game. You CANNOT instantiate (make objects of) an interface. Game game = new Game(); is NOT legal code. You can, however, refer to an object that implements an interface by the type of the interface.

Question 17

Integer.MAX_VALUE is determine by ____

Answer 17

the size of int, which is ALWAYS 4 bytes, no matter the platform that Java is running. Java source code is compiled into bytecodes, which may then be run on any computer that has a Java Virtual Machine installed.

Question 18

How to compare if two strings hold the same values?

Answer 18

str1.equals(str2) OR str1.compareTo(str2)

Question 19

A class does not NEED to define a ________

Answer 19

constructor. If it does not, then Object’s is called

Question 20

When overriding Object’s equals method, the input to the function must be of type _____

Answer 20

Object

Question 21

Constructors’ return type must be declared void

Answer 21

FALSE. constructors do not have return types

Question 22

If a class implements an interface and fails to define ALL the methods of that interface, then the class must be declared

Answer 22

ABSTRACT

Question 23

_____ AND ______ have NO “.equals” methods, but ______ and ________ DO

Answer 23

int, double, Integer, Double

Question 24

if (!somethingIsFalse) explained

Answer 24

the “if” will only be passed if the !somethingIsFalse is true. that means that somethingIsFalse must be false.

Question 25

You cannot ________ an abstract class, but you can declare ________ or _________ of its type.

Answer 25

instantiate, variables, arrays

Question 26

If “list” is an ArrayList with two elements, attempting list.get(list.size()) will return a __________ error.

Answer 26

IndexOutOfBounds

Question 27

String[] msg = new String[2]

msg[0].substring(0, 2)

Answer 27

msg[0] is not defined so you cannot call its methods. This will throw a NullPointerException

Question 28

When designing a class hierarchy:

Answer 28

A superclass should contain the data and functionality that are common to all subclasses that inherit from the superclass. A superclass’ data does NOT necessarily all have to be public.

Question 29

In general, if the recursive call is made (assuming everything else works) BEFORE the printing:

Answer 29

the printed recursion will go in order. vice versa

Question 30

if ( (a+b) * (a-b) != (ab) - (bb) )

is what:

Answer 30

true. Roundoff error makes the if condition true. Exact equality never works. One should instead take the difference and see if it’s less than some acceptable value.

Question 31

Adding elements into an ArrayList at n

Answer 31

inserts it at n and pushes all other elements (including the one previously at n) down one in the list

Question 32

Classes Salsa and Swing implement Dance.
Both perform(new Salsa()) and perform(new Swing()) are valid. The definitions of the performer method in Dance could be:

Answer 32

perform(Dance dance) OR perform(Object dance). BOTH are valid

Question 33

Even when given an instance of a class in another class, calling c.value (with value private in class C) will:

Answer 33

give a syntax error UNLESS the call is made in c.

Question 34

If HouseForSale extends House, making a new HouseForSale will run HouseForSale’s constructor which will call _______

Answer 34

House’s constructor BEFORE anything else, whether it is explicitly written or not. If House does not have a no args constructor, than you MUST manually call “super(something)” BEFORE anything else, otherwise you will get a syntax error.

Question 35

If a superclass and its subclass each have methods with the same name and input(s):

Answer 35

then calling the method from the subclass will run the subclass’ version of the method. If it cannot find the method in the subclass, then the parent’s version will be run

Question 36

Static methods cannot access or modify any _____ variables and cannot refer to ________ because ________ is undefined when a static method is running

Answer 36

instance, this, this

Question 37

Non-static methods, however, CAN refer to ______ variables

Answer 37

static

Question 38

ArrayList IS a _____

Answer 38

List. it inherits all of its methods. ArrayList list = new List();
IS ILLEGAL CODE

Question 39

Interfaces can be used when:

Answer 39

two classes exist that are not connected at all, but both have similar methods (maybe both are washable). Then implement this interface on the two classes.

Question 40

A feature of data that is used for a binary search but not necessarily for a sequential search is:

Answer 40

order of data. The binary search algorithm depends upon the list being sorted.

Question 41

When sorted biggest to smallest with insertionSort, which list will need the fewest changes of position for individual elements?

Answer 41

Whichever list has the fewest elements out of order, regardless of how far away they are from their correct position in the list. (Also regardless of whether this element needs to be moved to the right or to the left).

Question 42

When sorted biggest to smallest with insertionSort, which list will need the greatest number of changes in position?

Answer 42

The list that is sorted in reverse order (or closest to reverse order).

Question 43

Assuming mergeSort will be used to sort an array arr of n integers into increasing order. What is the purpose of the merge method in the mergeSort algorithm?

Answer 43

merge two sorted parts of arr into a single sorted array

Question 44

Creating a class Library that has an ArrayList of type Book, and testing the code on Book first is an example of what development?

Answer 44

bottom-up

Question 45

if secondTestMethod() changes an array, then System.out.print(array) returns

Answer 45

the original array.

Question 46

list.add(list.size(), something) does NOT return an error because:

Answer 46

list.add(list.size(), something) adds the variable to the end of the list.

Question 47

The number of _______ for _____ sort is independent of the initial arrangement of elements

Answer 47

comparisons, selection

Question 48

String s = “holy”
s.substring(4)
returns ?

Answer 48

an empty string. NOTE: if substring(5) is called (greater than the length of “holy”) then you will get an IndexOutOfBoundsException

Question 49

Composition Definition:

Answer 49

Composition is the has-a relationship. (vs. inheritance -> is-a relationship) For this question: ArrayList list, was in the Library class

Question 50

Encapsulation definition:

Answer 50

Combining an object’s data and methods into a single unit called a class is known as encapsulation.