AP CSP Practice Test on Arrays (ArrayList and 2D arrays)

Last Updated on August 9, 2024

AP CSP Practice Test on Arrays (ArrayList and 2D arrays) Prepare for the College Board’s Advanced Placement® (AP®) Computer Science Principles (CSP) exam Unit 6: Array, Unit 7: ArrayList, and Unit 8: 2D Array Multiple Choice Question Answers.

Unit 6: Array (10%–15% ): Topics may include: Representing multiple related items as array objects, Traversing an array by accessing the elements using iteration statements, Standard algorithms that utilize array traversals to perform functions.

Unit 7: ArrayList (2.5%–7.5% ): Topics may include: Representing collections of related object reference data using ArrayList objects, Traversing an ArrayList by accessing the elements using iteration statements, Standard algorithms that utilize ArrayList traversals to perform functions, Searching and sorting using standard algorithms, Ethical issues around data collections

Unit 8: 2D Array (7.5%–10%) Topics may include: Representing collections of data as arrays of arrays, or 2D arrays, Traversing a 2D array by accessing the elements using nested iteration statements

AP CSP Practice Test on Arrays

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AP CSP Practice Test - Unit 6: Array, Unit 7: ArrayList and Unit 8: 2D Array

AP CSP Practice Test
Unit 6: Array, Unit 7: ArrayList and Unit 8: 2D Array
Total Items: 36
Explanation: Yes
Free Test, No Registration is required

1 / 36

public class Address
{
private String name;
private String street;
private String city;
private String state;
private String zip;
//constructors
...
//accessors
public String getName()
{ return name; }
public String getStreet()
{ return street; }
public String getCity()
{ return city; }
public String getState()
{ return state; }
public String getZip()
{ return zip; }
}
public class Student
{
private int idNum;
private double gpa;
private Address address;
//constructors
...
//accessors
public Address getAddress()
{ return address; }
public int getIdNum()
{ return idNum; }
public double getGpa()
{ return gpa; }
}

A client method has this declaration, followed by code to initialize the list:

Address[] list = new Address[100];

Here is a code segment to generate a list of names only.

for (Address a : list)
/* line of code */

Which is a correct /* line of code */?

(A) System.out.println(list.getName());

(B) System.out.println(a.getName());

(C) System.out.println(a);

(D) System.out.println(list[i].getName());

(E) System.out.println(a[i]);

In a for-each loop, a represents each Address object, so a.getName() is the correct way to access the name.

2 / 36

Finding Index of First Negative Integer

The following program segment is intended to find the index of the first negative integer in arr[0] . . . arr[N-1], where arr is an array of N integers:

int i = 0;
while (arr[i] >= 0) {
i++;
}
location = i;

This segment will work as intended

(A) always.

(B) never.

(C) whenever arr contains at least one negative integer

(D) whenever arr contains at least one nonnegative integer.

(E) whenever arr contains no negative integers.

The loop will work if there is at least one negative integer in the array; otherwise, it will cause an ArrayIndexOutOfBoundsException.

3 / 36

Consider the following code segment, applied to list, an ArrayList of Integer values.

int len = list.size();
for (int i = 0; i < len; i++)
{
list.add(i + 1, new Integer(i));
Object x = list.set(i, new Integer(i + 2));
}

If list is initially 6 1 8, what will it be following execution of the code segment?

(A) 2 3 4 2 1 8

(B) 2 3 4 6 2 2 0 1 8

(C) 2 3 4 0 1 2

(D) 2 3 4 6 1 8

(E) 2 3 3 2

4 / 36

Refer to the following code segment. You may assume that array arr1 contains elements arr1[0], arr1[1], . . . , arr1[N-1], where N = arr1.length.

int count = 0;
for (int i = 0; i < N; i++) {
if (arr1[i] != 0) {
arr1[count] = arr1[i];
count++;
}
}
int[] arr2 = new int[count];
for (int i = 0; i < count; i++) {
arr2[i] = arr1[i];
}

If array arr1 initially contains the elements 0, 6, 0, 4, 0, 0, 2 in this order, what will arr2 contain after execution of the code segment?

(A) 6, 4, 2

(B) 0, 0, 0, 0, 6, 4, 2

(C) 6, 4, 2, 4, 0, 0, 2

(D) 0, 6, 0, 4, 0, 0, 2

(E) 6, 4, 2, 0, 0, 0, 0

The code copies non-zero elements to arr1 starting from index 0 and then copies these elements to arr2.

5 / 36

The following code fragment is intended to find the smallest value in arr[0] ... arr[n-1]:

/** Precondition:
* - arr is an array, arr.length = n.
* - arr[0]...arr[n-1] initialized with integers.
* Postcondition: min = smallest value in arr[0]...arr[n-1].
*/
int min = arr[0];
int i = 1;
while (i < n)
{
i++;
if (arr[i] < min)
min = arr[i];
}

This code is incorrect. For the segment to work as intended, which of the following modifications could be made?

I: Change the line int i = 1; to `int i = 0; Make no other changes.

II: Change the body of the while loop to:

{
if (arr[i] < min)
min = arr[i];
i++;
}

III: Change the test for the while loop as follows: while (i <= n) Make no other changes.

(A) I only

(B) II only

(C) III only

(D) I and II only

(E) I, II, and III

6 / 36

Questions are based on the Coin and Purse classes given below:

/* A simple coin class */
public class Coin
{

private double value;
private String name;
//constructor
public Coin(double coinValue, String coinName)
{
value = coinValue;
name = coinName;
}
/** @return the value of this coin */
public double getValue()
{ return value; }
/** @return the name of this coin */
public String getName()
{ return name; }
/** @param obj a Coin object
* @return true if this coin equals obj; otherwise false
*/
public boolean equals(Object obj)
{ return name.equals(((Coin) obj).name); }
//Other methods are not shown.

}

/* A purse holds a collection of coins */
public class Purse
{

private List coins;
/** Creates an empty purse. */
public Purse()
{ coins = new ArrayList(); }
/** Adds aCoin to the purse.
* @param aCoin the coin to be added to the purse
*/
public void add(Coin aCoin)
{ coins.add(aCoin); }
/** @return the total value of coins in purse */
public double getTotal()
{ /* implementation not shown */}

}

Here is the getTotal method from the Purse class:

/** @return the total value of coins in purse */
public double getTotal()
{
double total = 0;
/* more code */
return total;
}

Which of the following is a correct replacement for / more code /?

(A) for (Coin c : coins) { c = coins.get(i); total += c.getValue(); }

(B) for (Coin c : coins) { Coin value = c.getValue(); total += value; }

(C) for (Coin c : coins) { Coin c = coins.get(i); total += c.getValue(); }

(D) for (Coin c : coins) { total += coins.getValue(); }

(E) for (Coin c : coins) { total += c.getValue(); }

Option (E) correctly iterates over each Coin in the coins list and adds its value to total. Options (A), (B), (C), and (D) either misuse variables or methods, leading to errors.

7 / 36

public class Address
{
private String name;
private String street;
private String city;
private String state;
private String zip;
//constructors
...
//accessors
public String getName()
{ return name; }
public String getStreet()
{ return street; }
public String getCity()
{ return city; }
public String getState()
{ return state; }
public String getZip()
{ return zip; }
}
public class Student
{
private int idNum;
private double gpa;
private Address address;
//constructors
...
//accessors
public Address getAddress()
{ return address; }
public int getIdNum()
{ return idNum; }
public double getGpa()
{ return gpa; }
}

Consider the following code segment:

for (Address addr : list)
{
/* more code */
}

Which is a correct replacement for /* more code */?

I System.out.println(list[i].getName());
System.out.println(list[i].getStreet());
System.out.print(list[i].getCity() + ", ");
System.out.print(list[i].getState() + " ");
System.out.println(list[i].getZip());

II System.out.println(addr.getName());
System.out.println(addr.getStreet());
System.out.print(addr.getCity() + ", ");
System.out.print(addr.getState() + " ");
System.out.println(addr.getZip());

III System.out.println(addr);

(A) I only

(B) II only

(C) III only

(D) I and II only

(E) I, II, and III

8 / 36

Refer to the following code segment. You may assume that arr is an array of int values.

int sum = arr[0], i = 0;
while (i < arr.length) {
i++;
sum += arr[i];
}

Which of the following will be the result of executing the segment?

(A) Sum of arr[0], arr[1], . . . , arr[arr.length-1] will be stored in sum.

(B) Sum of arr[1], arr[2], . . . , arr[arr.length-1] will be stored in sum.

(C) Sum of arr[0], arr[1], . . . , arr[arr.length] will be stored in sum.

(D) An infinite loop will occur.

(E) A run-time error will occur.

The code will try to access arr[arr.length], which is out of bounds, leading to an ArrayIndexOutOfBoundsException.

9 / 36

Refer to the method insert below:

/** @param list an ArrayList of String objects
* @param element a String object
* Precondition: list contains String values sorted
* in decreasing order.
* Postcondition: element inserted in its correct position in list.
*/

public void insert(List list, String element)
{

int index = 0;
while (element.compareTo(list.get(index)) < 0)
index++;
list.add(index, element);

}

Assuming that the type of element is compatible with the objects in the list, which is a true statement about the insert method?

(A) It works as intended for all values of element.

(B) It fails for all values of element.

(C) It fails if element is greater than the first item in list and works in all other cases.

(D) It fails if element is smaller than the last item in list and works in all other cases.

(E) It fails if element is either greater than the first item or smaller than the last item in list and works in all other cases.

10 / 36

Questions are based on the Coin and Purse classes given below:

/* A simple coin class */
public class Coin
{

private double value;
private String name;
//constructor
public Coin(double coinValue, String coinName)
{
value = coinValue;
name = coinName;
}
/** @return the value of this coin */
public double getValue()
{ return value; }
/** @return the name of this coin */
public String getName()
{ return name; }
/** @param obj a Coin object
* @return true if this coin equals obj; otherwise false
*/
public boolean equals(Object obj)
{ return name.equals(((Coin) obj).name); }
//Other methods are not shown.

}

/* A purse holds a collection of coins */
public class Purse
{

private List coins;
/** Creates an empty purse. */
public Purse()
{ coins = new ArrayList(); }
/** Adds aCoin to the purse.
* @param aCoin the coin to be added to the purse
*/
public void add(Coin aCoin)
{ coins.add(aCoin); }
/** @return the total value of coins in purse */
public double getTotal()
{ /* implementation not shown */}

}

Two coins are said to match each other if they have the same name or the same value. You may assume that coins with the same name have the same value and coins with the same value have the same name. A boolean method find is added to the Purse class:

/** @return true if the purse has a coin that matches aCoin,
* false otherwise
*/
public boolean find(Coin aCoin)
{
for (Coin c : coins)
{
/* code to find match */
}
return false;
}

Which is a correct replacement for / code to find match /?

I if (c.equals(aCoin)) return true;

II if ((c.getName()).equals(aCoin.getName())) return true;

III if ((c.getValue()).equals(aCoin.getValue())) return true;

(A) I only

(B) II only

(C) III only

(D) I and II only

(E) I, II, and III

Since equals checks for the same name, it will work. For name comparisons, c.getName().equals(aCoin.getName()) will also work. However, c.getValue().equals(aCoin.getValue()) is incorrect because getValue() returns a double, and double values are compared using ==, not equals.

11 / 36

Consider writing a program that reads the lines of any text file into a sequential list of lines. Which of the following is a good reason to implement the list with an ArrayList of String objects rather than an array of String objects?

(A) The get and set methods of ArrayList are more convenient than the [] notation for arrays.

(B) The size method of ArrayList provides instant access to the length of the list.

(C) An ArrayList can contain objects of any type, which leads to greater generality.

(D) If any particular text file is unexpectedly long, the ArrayList will automatically be resized. The array, by contrast, may go out of bounds.

(E) The String methods are easier to use with an ArrayList than with an array.

ArrayList dynamically resizes, whereas arrays have fixed sizes.

12 / 36

public class Address
{
private String name;
private String street;
private String city;
private String state;
private String zip;
//constructors
...
//accessors
public String getName()
{ return name; }
public String getStreet()
{ return street; }
public String getCity()
{ return city; }
public String getState()
{ return state; }
public String getZip()
{ return zip; }
}
public class Student
{
private int idNum;
private double gpa;
private Address address;
//constructors
...
//accessors
public Address getAddress()
{ return address; }
public int getIdNum()
{ return idNum; }
public double getGpa()
{ return gpa; }
}

Here is a method that locates the Student with the highest idNum:

/** Precondition: Array stuArr of Student is initialized.
* @return Student with highest idNum
*/
public static Student locate(Student[] stuArr) {
/* method body */
}

Which of the following could replace /* method body */ so that the method works as intended?

I

int max = stuArr[0].getIdNum();
for (Student student : stuArr)
if (student.getIdNum() > max) {
max = student.getIdNum();
return student;
}
return stuArr[0];

II

Student highestSoFar = stuArr[0];
int max = stuArr[0].getIdNum();
for (Student student : stuArr)
if (student.getIdNum() > max) {
max = student.getIdNum();
highestSoFar = student;
}
return highestSoFar;

III

int maxPos = 0;
for (int i = 1; i < stuArr.length; i++)
if (stuArr[i].getIdNum() > stuArr[maxPos].getIdNum())
maxPos = i;
return stuArr[maxPos];

(A) I only

(B) II only

(C) III only

(D) I and III only

(E) II and III only

13 / 36

Questions refer to the Ticket and Transaction classes below

public class Ticket
{

private String row;
private int seat;
private double price;
//constructor
public Ticket(String aRow, int aSeat, double aPrice)
{
row = aRow;
seat = aSeat;
price = aPrice;
}
//accessors getRow(), getSeat(), and getPrice()
...

}

public class Transaction
{

private int numTickets;
private Ticket[] tickList;
//constructor
public Transaction(int numTicks)
{

numTickets = numTicks;
tickList = new Ticket[numTicks];
String theRow;
int theSeat;
double thePrice;
for (int i = 0; i < numTicks; i++)
{

< read user input for theRow, theSeat, and thePrice >
...
/* more code */

}

}

/** @return total amount paid for this transaction */
public double totalPaid()
{

double total = 0.0;
/* code to calculate amount */
return total;

}

}

Which represents correct /* code to calculate amount */ in the totalPaid method?

(A) for (Ticket t : tickList) total += t.price;

(B) for (Ticket t : tickList) total += tickList.getPrice();

(C) for (Ticket t : tickList) total += t.getPrice();

(D) Transaction T; for (Ticket t : T) total += t.getPrice();

(E) Transaction T; for (Ticket t : T) total += t.price;

(C) correctly uses the getPrice() method to access the price of each Ticket and adds it to total.

14 / 36

Consider a class MatrixStuff that has a private instance variable:

private int[][] mat;

Refer to method alter below that occurs in the MatrixStuff class. (The lines are numbered for reference.)

Line 1: /** @param mat the matrix initialized with integers
Line 2: * @param c the column to be removed
Line 3: * Postcondition:
Line 4: * - Column c has been removed.
Line 5: * - The last column is filled with zeros.
Line 6: */
Line 7: public void alter(int[][] mat, int c)
Line 8: {
Line 9: for (int i = 0; i < mat.length; i++)
Line 10: for (int j = c; j < mat[0].length; j++)
Line 11: mat[i][j] = mat[i][j+1];
Line 12: //code to insert zeros in rightmost column
Line 13: ...
Line 14: }

The intent of the method alter is to remove column c. Thus, if the input matrix mat is

2 6 8 9
1 5 4 3
0 7 3 2

the method call alter(mat, 1) should change mat to

2 8 9 0
1 4 3 0
0 3 2 0

The method does not work as intended. Which of the following changes will correct the problem?

I

Change line 10 to
for (int j = c; j < mat[0].length - 1; j++)
and make no other changes.

II

Change lines 10 and 11 to
for (int j = c + 1; j < mat[0].length; j++)
mat[i][j-1] = mat[i][j];
and make no other changes.

III

Change lines 10 and 11 to
for (int j = mat[0].length - 1; j > c; j--)
mat[i][j-1] = mat[i][j];
and make no other changes.

(A) I only

(B) II only

(C) III only

(D) I and II only

(E) I, II, and III

15 / 36

Consider a class that has this private instance variable:

private int[][] mat;

The class has the following method, alter.

public void alter(int c)
{
for (int i = 0; i < mat.length; i++)
for (int j = c + 1; j < mat[0].length; j++)
mat[i][j-1] = mat[i][j];
}

If a 3 × 4 matrix mat is

1 3 5 7
2 4 6 8
3 5 7 9

then alter(1) will change mat to

(A)

(B)

(C)

(D)

(E)

alter(1) shifts elements in each row starting from column c+1 to the left by one position, which results in the last element of each row being overwritten.

16 / 36

Consider this class:

public class BingoCard
{

private int[] card;
/** Default constructor: Creates BingoCard with
* 20 random digits in the range 1 - 90.
*/
public BingoCard()
{ /* implementation not shown */ }
/* Display BingoCard. */
public void display()
{ /* implementation not shown */ }
...

}

A program that simulates a bingo game declares an array of BingoCard. The array has NUMPLAYERS elements, where each element represents the card of a different player. Here is a code segment that creates all the bingo cards in the game:

/* declare array of BingoCard */
/* construct each BingoCard */

Which of the following is a correct replacement for /* declare array of BingoCard */?

(A) int[] BingoCard = new BingoCard[NUMPLAYERS];

(B) BingoCard[] players = new int[NUMPLAYERS];

(C) BingoCard[] players = new BingoCard[20];

(D) BingoCard[] players = new BingoCard[NUMPLAYERS];

(E) int[] players = new BingoCard[NUMPLAYERS];

17 / 36

What will be output from the following code segment, assuming it is in the same class as the doSomething method?

int[] arr = {1, 2, 3, 4};
doSomething(arr);
System.out.print(arr[1] + " ");
System.out.print(arr[3]);

public void doSomething(int[] list) {
int[] b = list;
for (int i = 0; i < b.length; i++)
b[i] = i;
}

(A) 0 0

(B) 2 4

(C) 1 3

(D) 0 2

(E) 0 3

The doSomething method modifies arr to {0, 1, 2, 3}, so arr[1] is 1 and arr[3] is 3.

18 / 36

Which declaration will cause an error?

I: List stringList = new ArrayList();

II: List intList = new ArrayList();

III: ArrayList compList = new ArrayList();

(A) I only

(B) II only

(C) III only

(D) I and III only

(E) II and III only

19 / 36

Which of the following initializes an 8 × 10 matrix with integer values that are perfect squares? (0 is a perfect square.)

I int[][] mat = new int[8][10];

II int[][] mat = new int[8][10]; for (int r = 0; r < mat.length; r++) for (int c = 0; c < mat[r].length; c++) mat[r][c] = r * r;

III int[][] mat = new int[8][10]; for (int c = 0; c < mat[r].length; c++) for (int r = 0; r < mat.length; r++) mat[r][c] = c * c;

(A) I only

(B) II only

(C) III only

(D) I and II only

(E) I, II, and III

I only declares the matrix but does not initialize it with perfect squares.

II initializes the matrix where each row is filled with the square of the row index, which does not fulfill the requirement for all elements being perfect squares across rows and columns.

III initializes the matrix where each column is filled with the square of the column index, which is incorrect as it doesn’t use the correct index for perfect squares across both dimensions.

20 / 36

public class Address
{
private String name;
private String street;
private String city;
private String state;
private String zip;
//constructors
...
//accessors
public String getName()
{ return name; }
public String getStreet()
{ return street; }
public String getCity()
{ return city; }
public String getState()
{ return state; }
public String getZip()
{ return zip; }
}
public class Student
{
private int idNum;
private double gpa;
private Address address;
//constructors
...
//accessors
public Address getAddress()
{ return address; }
public int getIdNum()
{ return idNum; }
public double getGpa()
{ return gpa; }
}

A client method has this declaration:

Student[] allStudents = new Student[NUM_STUDS]; // NUM_STUDS is an int constant

Here is a code segment to generate a list of Student names only. (You may assume that allStudents has been initialized.)

for (Student student : allStudents)
/* code to print list of names */

Which is a correct replacement for /* code to print list of names */?

(A) System.out.println(allStudents.getName());

(B) System.out.println(student.getName());

(C) System.out.println(student.getAddress().getName());

(D) System.out.println(allStudents.getAddress().getName());

(E) System.out.println(student[i].getAddress().getName());

21 / 36

Consider the following method that will alter the matrix mat:

/** @param mat the initialized matrix
* @param row the row number
*/
public static void matStuff(int[][] mat, int row)
{

int numCols = mat[0].length;
for (int col = 0; col < numCols; col++)
mat[row][col] = row;

}

Suppose mat is originally

1 4 9 0
2 7 8 6
5 1 4 3

After the method call matStuff(mat,2), matrix mat will be

A

B

C

D

E

22 / 36

A simple Tic-Tac-Toe board is a 3 × 3 array filled with either X’s, O’s, or blanks. Here is a class for a game of Tic-Tac-Toe:

public class TicTacToe
{

private String[][] board;
private static final int ROWS = 3;
private static final int COLS = 3;
/** Construct an empty board. */
public TicTacToe()
{

board = new String[ROWS][COLS];
for (int r = 0; r < ROWS; r++)
for (int c = 0; c < COLS; c++)
board[r][c] = " ";

}
/** @param r the row number
* @param c the column number
* @param symbol the symbol to be placed on board[r][c]
* Precondition: The square board[r][c] is empty.
* Postcondition: symbol placed in that square.
*/
public void makeMove(int r, int c, String symbol)
{
board[r][c] = symbol;
}
/** Creates a string representation of the board, e.g.
* |o |
* |xx |
* | o|
* @return the string representation of board
*/
public String toString()
{
String s = ""; //empty string
/* more code */
return s;
}

}

Which segment represents a correct replacement for /* more code */ for the toString method?

Option A

for (int r = 0; r < ROWS; r++)
{
for (int c = 0; c < COLS; c++)
{
s = s + "|";
s = s + board[r][c];
s = s + "|\n";
}
}

Option B

for (int r = 0; r < ROWS; r++)
{
s = s + "|";
for (int c = 0; c < COLS; c++)
{
s = s + board[r][c];
s = s + "|\n";
}

Option C

for (int r = 0; r < ROWS; r++)
{
s = s + "|";
for (int c = 0; c < COLS; c++)
s = s + board[r][c];
}
s = s + "|\n";

Option D

for (int r = 0; r < ROWS; r++)
s = s + "|";
for (int c = 0; c < COLS; c++)
{
s = s + board[r][c];
s = s + "|\n";

Option E

for (int r = 0; r < ROWS; r++)
{
s = s + "|";
for (int c = 0; c < COLS; c++)
s = s + board[r][c];
s = s + "|\n";
}

Option A

Option B

Option C

Option D

Option E

23 / 36

Consider this program segment:

for (int i = 2; i <= k; i++)
if (arr[i] < someValue)
System.out.print("SMALL");

What is the maximum number of times that "SMALL" can be printed?

(A) 0

(B) 1

(C) k - 1

(D) k - 2

(E) k

The loop runs from i = 2 to i = k, so there are k - 1 possible iterations.

24 / 36

Questions refer to the Ticket and Transaction classes below

public class Ticket
{

private String row;
private int seat;
private double price;
//constructor
public Ticket(String aRow, int aSeat, double aPrice)
{
row = aRow;
seat = aSeat;
price = aPrice;
}
//accessors getRow(), getSeat(), and getPrice()
...

}

public class Transaction
{

private int numTickets;
private Ticket[] tickList;
//constructor
public Transaction(int numTicks)
{

numTickets = numTicks;
tickList = new Ticket[numTicks];
String theRow;
int theSeat;
double thePrice;
for (int i = 0; i < numTicks; i++)
{

< read user input for theRow, theSeat, and thePrice >
...
/* more code */

}

}

/** @return total amount paid for this transaction */
public double totalPaid()
{

double total = 0.0;
/* code to calculate amount */
return total;

}

}

Which of the following correctly replaces /* more code */ in the Transaction constructor to initialize the tickList array?

(A) tickList[i] = new Ticket(getRow(), getSeat(), getPrice());

(B) tickList[i] = new Ticket(theRow, theSeat, thePrice);

(C) tickList[i] = new tickList(getRow(), getSeat(), getPrice());

(D) tickList[i] = new tickList(theRow, theSeat, thePrice);

(E) tickList[i] = new tickList(numTicks);

(B) correctly creates a new Ticket object with the values theRow, theSeat, and thePrice, and assigns it to the tickList.

25 / 36

This question refers to the following method:

public static boolean isThere(String[][] mat, int row, int col,
String symbol)
{

boolean yes;
int i, count = 0;
for (i = 0; i < SIZE; i++)
if (mat[i][col].equals(symbol))
count++;
yes = (count == SIZE);
count = 0;
for (i = 0; i < SIZE; i++)
if (mat[row][i].equals(symbol))
count++;
return (yes || count == SIZE);

}

Now consider this code segment:

public final int SIZE = 8;
String[][] mat = new String[SIZE][SIZE];

Which of the following conditions on a matrix mat of the type declared in the code segment will by itself guarantee that

isThere(mat, 2, 2, "$")

will have the value true when evaluated?

I The element in row 2 and column 2 is "$"
II All elements in both diagonals are "$"
III All elements in column 2 are "$"

(A) I only

(B) III only

(C) I and II only

(D) I and III only

(E) II and III only

26 / 36

Consider this class:

public class Book
{

private String title;
private String author;
private boolean checkoutStatus;
public Book(String bookTitle, String bookAuthor)
{
title = bookTitle;
author = bookAuthor;
checkoutStatus = false;
}
/** Change checkout status. */
public void changeStatus()
{ checkoutStatus = !checkoutStatus; }
// Other methods are not shown.

}

A client program has this declaration:

Book[] bookList = new Book[SOME_NUMBER];

Suppose bookList is initialized so that each Book in the list has a title, author, and checkout status. The following piece of code is written, whose intent is to change the checkout status of each book in bookList:

for (Book b : bookList)
b.changeStatus();

Which is true about this code?

(A) The bookList array will remain unchanged after execution.

(B) Each book in the bookList array will have its checkout status changed, as intended.

(C) A NullPointerException may occur.

(D) A run-time error will occur because it is not possible to modify objects using the for-each loop.

(E) A logic error will occur because it is not possible to modify objects in an array without accessing the indexes of the objects.

27 / 36

The method changeNegs below should replace every occurrence of a negative integer in its matrix parameter with 0.

/** @param mat the matrix
* Precondition: mat is initialized with integers.
* Postcondition: All negative values in mat replaced with 0.
*/
public static void changeNegs(int[][] mat)
{
/* code */
}

Which is correct replacement for /* code */?

I

for (int r = 0; r < mat.length; r++)
for (int c = 0; c < mat[r].length; c++)
if (mat[r][c] < 0)
mat[r][c] = 0;

II

for (int c = 0; c < mat[0].length; c++)
for (int r = 0; r < mat.length; r++)
if (mat[r][c] < 0)
mat[r][c] = 0;

III

for (int[] row : mat)
for (int element : row)
if (element < 0)
element = 0;

(A) I only

(B) II only

(C) III only

(D) I and II only

(E) I, II, and III

28 / 36

Which of the following correctly initializes an array arr to contain four elements each with value 0?

I. int[] arr = {0, 0, 0, 0};
II. int[] arr = new int[4];
III. int[] arr = new int[4]; for (int i = 0; i < arr.length; i++) arr[i] = 0;

(A) I only

(B) III only

(C) I and III only

(D) II and III only

(E) I, II, and III

Explanation:

I correctly initializes the array with four elements, all set to 0.

II initializes the array with four elements, all set to 0 by default.

III initializes the array with four elements, all set to 0 by explicitly setting each element.

29 / 36

A two-dimensional array of double, rainfall, will be used to represent the daily rainfall for a given year. In this scheme, rainfall[month][day] represents the amount of rain on the given day and month. For example,

rainfall[1][15] is the amount of rain on Jan. 15
rainfall[12][25] is the amount of rain on Dec. 25

The array can be declared as follows:

double[][] rainfall = new double[13][32];

This creates 13 rows indexed from 0 to 12 and 32 columns indexed from 0 to 31, all initialized to 0.0. Row 0 and column 0 will be ignored. Column 31 in row 4 will be ignored, since April 31 is not a valid day. In years that are not leap years, columns 29, 30, and 31 in row 2 will be ignored since Feb. 29, 30, and 31 are not valid days.

Consider the method averageRainfall below:

/** Precondition:
* - rainfall is initialized with values representing amounts
* of rain on all valid days.
* - Invalid days are initialized to 0.0.
* - Feb 29 is not a valid day.
* Postcondition: Returns average rainfall for the year.
*/
public double averageRainfall(double rainfall[][])
{
double total = 0.0;
/* more code */
}

Which of the following is a correct replacement for /* more code */ so that the postcondition for the method is satisfied?

I

for (int month = 1; month < rainfall.length; month++)
for (int day = 1; day < rainfall[month].length; day++)
total += rainfall[month][day];
return total / (13 * 32);

II

for (int month = 1; month < rainfall.length; month++)
for (int day = 1; day < rainfall[month].length; day++)
total += rainfall[month][day];
return total / 365;

III

for (double[] month : rainfall)
for (double rainAmt : month)
total += rainAmt;
return total / 365;

(A) None

(B) I only

(C) II only

(D) III only

(E) II and III only

Option II correctly accounts for valid days in each month, including ignoring invalid days, and provides the correct average based on 365 days. Option III correctly handles the summation of all elements and divides by 365 to compute the average. Option I incorrectly divides by 13 * 32, which does not account for invalid days.

30 / 36

Consider this class:

public class BingoCard
{

private int[] card;
/** Default constructor: Creates BingoCard with
* 20 random digits in the range 1 - 90.
*/
public BingoCard()
{ /* implementation not shown */ }
/* Display BingoCard. */
public void display()
{ /* implementation not shown */ }
...

}

Assuming that players has been declared as an array of BingoCard, which of the following is a correct replacement for /* construct each BingoCard */?

I

for (BingoCard card : players)
card = new BingoCard();

II

for (BingoCard card : players)
players[card] = new BingoCard();

III

for (int i = 0; i < players.length; i++)
players[i] = new BingoCard();

(A) I only

(B) II only

(C) III only

(D) I and III only

(E) I, II, and III

31 / 36

Consider writing a program that produces statistics for long lists of numerical data. Which of the following is the best reason to implement each list with an array of int (or double), rather than an ArrayList of Integer (or Double) objects?

(A) An array of primitive number types is more efficient to manipulate than an ArrayList of wrapper objects that contain numbers.

(B) Insertion of new elements into a list is easier to code for an array than for an ArrayList.

(C) Removal of elements from a list is easier to code for an array than for an ArrayList.

(D) Accessing individual elements in the middle of a list is easier for an array than for an ArrayList.

(E) Accessing all the elements is more efficient in an array than in an ArrayList.

Primitive types are more efficient in terms of performance and memory usage compared to wrapper classes.

32 / 36

Consider these declarations:

List strList = new ArrayList();
String ch = " ";
Integer intOb = new Integer(5);

Which statement will cause an error?

(A) strList.add(ch);

(B) strList.add(new String("handy andy"));

(C) strList.add(intOb.toString());

(D) strList.add(ch + 8);

(E) strList.add(intOb + 8);

The intOb + 8 expression results in an int, which cannot be added directly to a List<String>. Other expressions are valid because they either convert the Integer to a String or concatenate a String with another value.

33 / 36

Questions refer to the Ticket and Transaction classes below

public class Ticket
{

private String row;
private int seat;
private double price;
//constructor
public Ticket(String aRow, int aSeat, double aPrice)
{
row = aRow;
seat = aSeat;
price = aPrice;
}
//accessors getRow(), getSeat(), and getPrice()
...

}

public class Transaction
{

private int numTickets;
private Ticket[] tickList;
//constructor
public Transaction(int numTicks)
{

numTickets = numTicks;
tickList = new Ticket[numTicks];
String theRow;
int theSeat;
double thePrice;
for (int i = 0; i < numTicks; i++)
{

< read user input for theRow, theSeat, and thePrice >
...
/* more code */

}

}

/** @return total amount paid for this transaction */
public double totalPaid()
{

double total = 0.0;
/* code to calculate amount */
return total;

}

}

Suppose it is necessary to keep a list of all ticket transactions. Assuming that there are NUMSALES transactions, a suitable declaration would be:

(A) Transaction[] listOfSales = new Transaction[NUMSALES];

(B) Transaction[] listOfSales = new Ticket[NUMSALES];

(C) Ticket[] listOfSales = new Transaction[NUMSALES];

(D) Ticket[] listOfSales = new Ticket[NUMSALES];

(E) Transaction[] Ticket = new listOfSales[NUMSALES];

34 / 36

Assume that a square matrix mat is defined by

int[][] mat = new int[SIZE][SIZE];
//SIZE is an integer constant >= 2

What does the following code segment do?

for (int i = 0; i < SIZE - 1; i++)
for (int j = 0; j < SIZE - i - 1; j++)
swap(mat, i, j, SIZE - j - 1, SIZE - i - 1);

You may assume the existence of this swap method:

/** Interchange mat[a][b] and mat[c][d]. */
public void swap(int[][] mat, int a, int b, int c, int d)

(A) Reflects mat through its major diagonal. For example,

(B) Reflects mat through its minor diagonal. For example

*C) Reflects mat through a horizontal line of symmetry. For example,

(D) Reflects mat through a vertical line of symmetry. For example,

(E) Leaves mat unchanged

35 / 36

Let list be an ArrayList containing these elements: 2 5 7 6 0 1.

Which of the following statements would not cause an error to occur? Assume that each statement applies to the given list, independent of the other statements.

(A) Object ob = list.get(6);

(B) Integer intOb = list.add(3.4);

(C) list.add(6, 9);

(D) Object x = list.remove(6);

(E) Object y = list.set(6, 8);

(C) is valid because list.add(6, 9) inserts the integer 9 at index 6, which is within the valid range for insertion.

36 / 36

Refer to the match method below:

/** @param v an array of int sorted in increasing order
* @param w an array of int sorted in increasing order
* @param N the number of elements in array v
* @param M the number of elements in array w
* @return true if there is an integer k that occurs
* in both arrays; otherwise returns false
* Precondition:
* v[0]..v[N-1] and w[0]..w[M-1] initialized with integers.
* v[0] < v[1] < .. < v[N-1] and w[0] < w[1] < .. < w[M-1].
*/
public static boolean match(int[] v, int[] w, int N, int M)
{

int vIndex = 0, wIndex = 0;
while (vIndex < N && wIndex < M)
{
if (v[vIndex] == w[wIndex])
return true;
else if (v[vIndex] < w[wIndex])
vIndex++;
else
wIndex++;

}
return false;
}

Assuming that the method has not been exited, which assertion is true at the end of every execution of the while loop?

(A) v[0]..v[vIndex-1] and w[0]..w[wIndex-1] contain no common value, vIndex ≤ N and wIndex ≤ M.

(B) v[0]..v[vIndex] and w[0]..w[wIndex] contain no common value, vIndex ≤ N and wIndex ≤ M.

(C) v[0]..v[vIndex-1] and w[0]..w[wIndex-1] contain no common value, vIndex ≤ N-1 and wIndex ≤ M-1.

(D) v[0]..v[vIndex] and w[0]..w[wIndex] contain no common value, vIndex ≤ N-1 and wIndex ≤ M-1.

(E) v[0]..v[N-1] and w[0]..w[M-1] contain no common value, vIndex ≤ N and wIndex ≤ M.

At the end of each loop iteration, the values in v[0]..v[vIndex-1] and w[0]..w[wIndex-1] have been checked and contain no common values. The indices vIndex and wIndex do not exceed the bounds of their respective arrays.

Your score is

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