1Z0-811 Arrays and Methods Practice Test 3 — 15 Questions

Question 1

Which of the following correctly uses the shorthand array initializer to declare and initialize an array of strings with the elements "A", "B", and "C"?

Accepted Answer

String[] arr = {"A", "B", "C"};. Option D correctly uses the shorthand array initializer with curly braces directly in the declaration. Option A uses the full syntax with the 'new' keyword, which is also valid but not the shorthand. Option B is wrong because it uses parentheses. Option C is wrong because it uses square brackets.

Answer

String[] arr = new String[] {"A", "B", "C"};

Answer

String[] arr = ("A", "B", "C");

Answer

String[] arr = ["A", "B", "C"];

Question 2

Given the method: 'public static void swapFirstTwo(int[] arr) { int temp = arr[0]; arr[0] = arr[1]; arr[1] = temp; }'. What is the effect of calling this method with an array of length 1?

Accepted Answer

An ArrayIndexOutOfBoundsException is thrown.. The method accesses arr[0] and arr[1] without verifying the array length. When called with an array of length 1, index 1 is out of bounds because valid indices are 0 only. Java performs runtime bounds checking, so an ArrayIndexOutOfBoundsException is thrown.

Answer

The first element is swapped with itself.

Answer

A new array with length 2 is returned.

Answer

The array remains unchanged.

Question 3

A developer writes a method that accepts a variable number of int arguments and returns their product. Which method signature correctly implements this?

Accepted Answer

public static int product(int... nums). The syntax `int... nums` is the proper Java varargs syntax, allowing a method to accept zero or more `int` arguments, which are then treated as an array inside the method. This enables the developer to call `product(2, 3, 4)` or `product()` and compute the product by iterating over the array.

Answer

public static int product(int[] nums)

Answer

public static int product(int nums...)

Answer

public static int product(int... nums, int extra)

Question 4

What is the output of the following code? int[] a = {1,2,3}; int[] b = a; b[0] = 99; System.out.println(a[0]);

Accepted Answer

99. In Java, arrays are reference types. When `int[] b = a;` is executed, `b` does not create a new array; it simply references the same array object as `a`. Therefore, modifying `b[0]` directly changes the element in the original array `a`, so `a[0]` prints 99.

Answer

0

Answer

1

Answer

Compilation error

Question 5

Which of the following correctly describes the effect of the method call 'Arrays.sort(myArray)' on an array of objects that do not implement Comparable?

Accepted Answer

A ClassCastException is thrown at runtime.. When `Arrays.sort(myArray)` is called on an array of objects that do not implement the `Comparable` interface, the method attempts to cast elements to `Comparable` to compare them. Since the objects do not implement `Comparable`, a `ClassCastException` is thrown at runtime. The `Arrays.sort(Object[])` method requires that all elements implement `Comparable`; otherwise, it cannot determine a natural ordering.

Answer

The code does not compile because Arrays.sort requires a Comparator.

Answer

The array is sorted using the natural order of the elements.

Answer

The array is sorted using the order defined by the elements' equals method.

Question 6

Which TWO statements are true about method overloading in Java?

Accepted Answer

Overloaded methods can have different parameter lists.. Option B is correct because method overloading is defined by methods sharing the same name but differing in their parameter lists, which may vary in the number, types, or order of parameters. Option C is correct because overloaded methods must share the same method name; that shared name is what makes them overloaded rather than simply distinct methods. Option A is incorrect because overloaded methods may have different numbers of parameters, which is one of the valid ways to distinguish them. Option D is incorrect because return type alone cannot distinguish overloaded methods, and overloads are not required to have different return types. Option E is incorrect because methods with different names are not overloaded; they are simply different methods.

Answer

Overloaded methods must have the same number of parameters.

Answer

Overloaded methods must have different return types.

Answer

Overloaded methods can have different names.

Question 7

Which TWO statements are true about passing arrays to methods in Java?

Accepted Answer

The method can modify the elements of the array.. Option B is correct because Java passes the array's reference by value, so the method receives a reference that points to the same underlying array object; any assignment to an element such as arr[0] = 5 is therefore visible to the caller. Option D is correct because Java is strictly pass-by-value, and for arrays the value being passed is a copy of the reference (the memory address) to the array object, not a copy of the array's contents. Option A is incorrect because reassigning the parameter (e.g., arr = new int[5]) only changes the local copy of the reference and does not affect the caller's original array variable. Option C is incorrect because changes to array elements are reflected without returning the array, since both references point to the same object. Option E is incorrect because a method can always determine the array's length via the array's length field (e.g., arr.length).

Answer

The method can reassign the original array variable to a new array.

Answer

The method must return the array to reflect any changes.

Answer

The method cannot determine the size of the array.

Question 8

A team is developing a Java application for an online store. The application has a class 'Inventory' that maintains an array of 'Product' objects. The method 'public void addProduct(Product p)' is intended to add a product to the array. The current implementation uses a fixed-size array of length 100. However, the business has grown, and the array may exceed its capacity. The team needs a solution that allows dynamic resizing without changing the method signature. Which approach should the team take?

Accepted Answer

Modify the method to use an ArrayList internally and keep the signature.. Using an ArrayList internally allows the array to dynamically resize as needed, while keeping the method signature unchanged. The method still accepts a Product parameter, but the internal implementation leverages ArrayList's automatic capacity management, eliminating the fixed-size constraint.

Answer

Change the method signature to accept a Product[] array and copy all elements.

Answer

Use a Collection<Product> as parameter and convert to array.

Answer

Change the return type to boolean and return false if array is full.

Question 9

A developer is working on a Java program that processes sensor data. The data is stored in a 2D array 'double[][] readings', where each row represents a sensor and each column a time interval. The method 'public static double[] averagePerSensor(double[][] data)' should compute the average reading for each sensor (row) and return a 1D array of averages. The developer writes the following implementation: 'double[] result = new double[data.length]; for (int i = 0; i < data.length; i++) { double sum = 0; for (int j = 0; j < data[i].length; j++) { sum += data[i][j]; } result[i] = sum / data[i].length; } return result;'. However, the program sometimes throws a NullPointerException. What is the most likely cause?

Accepted Answer

One or more rows in the 2D array are null.. The NullPointerException occurs because the code attempts to access `data[i].length` when `data[i]` is null. In Java, a 2D array is an array of arrays, and any row can be null. The code does not check for null rows before iterating over the columns, so if a row is null, accessing `data[i][j]` or `data[i].length` throws a NullPointerException. Option C correctly identifies this as the most likely cause.

Answer

The method returns a double[] but should return double[][].

Answer

The rows have different numbers of columns.

Answer

The outer loop uses data[i].length instead of data.length.

Question 10

Arrange the steps to create an object from a class in Java in the correct order.

Accepted Answer

Define the class, then declare a variable, then instantiate with new, then assign to variable, then use the object.. First define the class, then declare a variable, instantiate with new, assign to variable, and then use the object.

Answer

Define the class, then instantiate the object, then declare a variable, then assign to variable, then use the object.

Answer

Declare a variable, then define the class, then instantiate the object, then assign to variable, then use the object.

Answer

Instantiate the object, then define the class, then declare a variable, then assign to variable, then use the object.

Question 11

A banking application stores daily transaction amounts in an array. Which declaration correctly creates an array of 31 double values?

Accepted Answer

double[] transactions = new double[31];. It uses the proper syntax to declare an array of double values and initializes it with a size of 31, which allocates memory for 31 double elements, each defaulting to 0.0. In Java, the array size must be specified when using the 'new' keyword, and the index range is 0 to 30, accommodating exactly 31 daily transaction amounts.

Answer

double transactions[] = new double[30];

Answer

int[] transactions = new int[31];

Answer

double[] transactions = new double[];

Question 12

Given the array declaration: int[] data = new int[5];, what is the value of data[2] after initialization?

Accepted Answer

0. In Java, when an array of primitive type `int` is created using `new int[5]`, all elements are automatically initialized to the default value for `int`, which is `0`. Therefore, `data[2]` (the third element) holds the value `0` after initialization.

Answer

2

Answer

false

Answer

null

Question 13

Consider a method that takes an int array and modifies it: public static void doubleArray(int[] arr) { for (int i = 0; i < arr.length; i++) { arr[i] *= 2; } }. What is the output of: int[] nums = {1, 2, 3}; doubleArray(nums); System.out.println(nums[1]);

Accepted Answer

4. The method `doubleArray` multiplies each element of the array by 2. The array `nums` is passed by reference, so modifications inside the method affect the original array. After execution, `nums[1]` (originally 2) becomes 4, which is printed.

Answer

8

Answer

2

Answer

3

Question 14

A developer writes two methods: public void process(int a) { ... } and public void process(double a) { ... }. Which method is called by process(10)?

Accepted Answer

The method with int parameter. Java selects the most specific overloaded method at compile time. When calling process(10), the integer literal 10 is an int, so the compiler prefers the method with the int parameter over the double parameter, as no implicit widening conversion is required.

Answer

The method with double parameter

Answer

Compilation error: ambiguous call

Answer

Runtime error: NoSuchMethod