Unit 6 Progress Check: MCQ

Consider the following code segment.

int[] arr = {10, 20, 30, 40, 50};

for(int x = 1; x < arr.length - 1; x++) {

arr[x + 1] = arr[x] + arr[x + 1];

}

Which of the following code segments would correctly set the first two elements of array arr to 10 so that the new value of array arr will be {10, 10, 3, 4, 5}?

• {10, 20, 30, 70, 120}

• {10, 20, 50, 90, 50}

• {10, 20, 50, 90, 140}

• {10, 30, 60, 100, 50}

• {10, 30, 60, 100, 150}

Answer explanation

Correct. The code line arr[0] = 10; sets the first element to 10, while the code line arr[1] =10; sets the second element to 10.

Consider the following method.

public int[] transform(int[] a) { a[0]++; a[2]++; return a; }

The following code segment appears in a method in the same class as transform.

/* missing code */ arr = transform(arr);

After executing the code segment, the array arr should contain {1, 0, 1, 0}. Which of the following can be used to replace /* missing code */ so that the code segment works as intended?

I. int[] arr = {0, 0, 0, 0};

II. int[] arr = new int[0];

III. int[] arr = new int[4];

• I only

• II only

• III only

• I and II

• I and III

Answer explanation

Correct. The transform method increases the first and third elements of the array by 1. In order to produce the intended result, the array passed to the method should contain {0, 0, 0, 0}. Code segment I works as intended. This statement uses an initializer list to create an array with four elements, each equal to 0. Code segment II does not work as intended. The statement creates a new array of length 0 (an array with no elements). Code segment III works as intended. The statement creates a new array of length 4, whose elements are each assigned the default value 0.

Consider the following method, which is intended to return the number of strings of length greater than or equal to 3 in an array of String objects.

public static int checkString(String[] arr) {

int count = 0;

for (int k = 0; k < arr.length; k++) {

if (arr[k].length() >= 3) {

count++; }

}

return count;

}

Which of the following code segments compile without error?

I. checkString(new String[]);

II. checkString(new String[0]);

III. String[] str = {"cat", "dog"}; checkString(str);

• I only

• II only

• III only

• I and II

• I and III

Answer explanation

The size of an array must be established when the array is created, either explicitly by specifying the size within the brackets or implicitly by using an initializer list. Statement I does not compile because the array size is missing. Statement II compiles because it correctly creates an array of size 0. Statement III compiles because it creates an array of size 2, using an initializer list.

Consider the following code segment.

int[] arr = {10, 20, 30, 40, 50};

for(int x = 1; x < arr.length - 1; x++) {

arr[x + 1] = arr[x] + arr[x + 1]; }

Which of the following represents the contents of arr after the code segment has been executed?

• {10, 20, 30, 70, 120}

• {10, 20, 50, 90, 50}

• {10, 20, 50, 90, 140}

• {10, 30, 60, 100, 50}

• {10, 30, 60, 100, 150}

Answer explanation

The code starts with the second element of the array (i.e., the element at index 1) and adds the current element to the next element of the array. The code will set the third element to 20 + 30, which is 50; it will then set the fourth element to 50 + 40, which is 90; finally, it will set the last element to 90 + 50, which is 140.

Consider the following code segment.

int[] arr = {4, 3, 2, 1, 0}; int total = 0; for (int k = 0; k <= total; k++) {

if (arr[k] % 2 == 0) {

total += arr[k]; } else { total -= arr[k]; }

}

System.out.print(total);

What, if anything, is printed as a result of executing the code segment?

• 2

• 1

• 0

• -4

• Nothing is printed because the code segment causes a runtime error.

Answer explanation

During the first iteration of the for loop, the Boolean expression arr[0] % 2 == 0 or 4 % 2 == 0 evaluates to true, so total is incremented by 4, becoming 4. During the second iteration of the for loop, the Boolean expression arr[1] % 2 == 0 or 3 % 2 == 0 evaluates to false, so total is decremented by 3, becoming 1. At this point, the Boolean expression k <= total or 2 <= 1 evaluates to false, and the for loop terminates. The current value of total, 1, is printed.

The array fruits is declared below.

String [] fruits = {"apples", "bananas", "cherries", "dates"};

Which of the following code segments will cause an ArrayIndexOutOfBoundsException?

I. for (int i = 0; i <= fruits.length; i++) {

System.out.println(fruits[i]); }

II. for (int i = 0; i <= fruits.length - 1; i++) {

System.out.println(fruits[i]); }

III. for (int i = 1; i <= fruits.length; i++) {

System.out.println(fruits[i - 1]); }

• I only

• II only

• I and III only

• II and III only

• I, II, and III

Answer explanation

Code segment I iterates i from 0 to 4. The last array element is at index 3, so an ArrayIndexOutOfBoundsException occurs when attempting to access the element at index 4. Code segment II iterates i from 0 to 3. It accesses each element of the array without error. Code segment III iterates i from 1 to 4. Since it accesses array elements at index i - 1, it accesses the array elements at indexes 0 to 3 without error.

The Fibonacci numbers are a sequence of integers. The first two numbers are 1 and 1. Each subsequent number is equal to the sum of the previous two integers. For example, the first seven Fibonacci numbers are 1, 1, 2, 3, 5, 8, and 13.

The following code segment is intended to fill the fibs array with the first ten Fibonacci numbers. The code segment does not work as intended.

int[] fibs = new int[10];

fibs[0] = 1;

fibs[1] = 1;

for (int j = 1; j < fibs.length; j++) {

fibs[j] = fibs[j - 2] + fibs[j - 1]; }

Which of the following best identifies why the code segment does not work as intended?

• In the for loop header, the initial value of j should be 0.

• In the for loop header, the initial value of j should be 2.

• The for loop condition should be j < fibs.length - 1.

• The for loop condition should be j < fibs.length + 1.

• The for loop should increment j by 2 instead of by 1.

Answer explanation

Correct. If j starts at 1, the attempt to access fibs[j - 2] during the first loop iteration will throw an ArrayIndexOutOfBoundsException. Starting the loop at j = 2 avoids this error.

Consider the following code segment. int[] numbers = {1, 2, 3, 4, 5, 6}; for (int i = 0; i < numbers.length; i++) { System.out.println(numbers[i]); } Which of the following for loops produces the same output as the code segment?

int[] numbers = {1, 2, 3, 4, 5, 6};

for (int i = 0; i < numbers.length; i++) {

System.out.println(numbers[i]); }

Which of the following code snippets correctly uses an enhanced for loop to print each element in the array 'numbers'?

• for (int x : numbers) { System.out.println(numbers[x]); }

• for (int x : numbers) { System.out.println(numbers); }

• for (int x : numbers) { System.out.println(x); }

• for (numbers : int x) { System.out.println(numbers[x]); }

• for (numbers : int x) { System.out.println(x); }

Answer explanation

Correct. The enhanced for loop variable x is correctly declared as an int data type. For each iteration of the enhanced for loop, x is assigned a copy of an element from the array numbers. The println method is passed that value to be printed.

Consider the following class definition.

public class Toy { private int yearFirstSold; public int getYearFirstSold() { return yearFirstSold; } /* There may be instance variables, constructors, and other methods not shown. */ }

The following code segment, which appears in a class other than Toy, prints the year each Toy object in toyArray was first sold by its manufacturer. Assume that toyArray is a properly declared and initialized array of Toy objects.

for (Toy k : toyArray) { System.out.println(k.getYearFirstSold()); }

Which of the following could be used in place of the given code segment to produce the same output?

I. for (int k = 0; k < toyArray.length; k++) { System.out.println(getYearFirstSold(k)); }

II. for (int k = 0; k < toyArray.length; k++) { System.out.println(k.getYearFirstSold()); }

III. for (int k = 0; k < toyArray.length; k++) { System.out.println(toyArray[k].getYearFirstSold()); }

• I only

• II only

• III only

• I and II

• II and III

Answer explanation

Code segment I uses the loop control variable k improperly, as a parameter for the getYearFirstSold method rather than as an array index. Code segment II also uses the loop control variable k improperly, as an object reference rather than as an array index. Code segment III uses the loop control variable k as an index into toyArray and the expression toyArray[k] as the required Toy object reference for the getYearFirstSold method call.

Consider the following two code segments.

I. int[] arr = {1, 2, 3, 4, 5}; for (int x = 0; x < arr.length; x++) { System.out.print(arr[x + 3]); }

II. int[] arr = {1, 2, 3, 4, 5}; for (int x : arr) { System.out.print(x + 3); }

Which of the following best describes the behavior of code segment I and code segment II?

• Both code segment I and code segment II will print 45.

• Both code segment I and code segment II will print 45678.

• Code segment I will cause an ArrayIndexOutOfBoundsException and code segment II will print 45.

• Code segment I will cause an ArrayIndexOutOfBoundsException and code segment II will print 45678.

• Both code segment I and code segment II will cause an ArrayIndexOutOfBoundsException.

Answer explanation

The first iteration of the for loop will print arr[0 + 3], or 4. The second iteration will print arr[1 + 3], or 5. The third iteration will attempt to access arr[2 + 3]. Since arr has five elements, the valid array indices are from 0 to 4, inclusive. Attempting to access arr[5] will cause an ArrayIndexOutOfBoundsException. Code segment II uses the enhanced for In the first iteration of the loop, x is 1 and 1 + 3, or 4 is printed. During the next iteration of the loop, x is 2 and 2 + 3, or 5 is printed. As x takes on the values 3, 4, and 5 for the remaining loop iterations, 6, 7, and 8 will be printed.