1Z0-811 Arrays and Methods Practice Test 2 — 15 Questions

Question 1

Which of the following is not a valid array variable declaration in Java?

Accepted Answer

int arr;. `int arr;` declares a simple integer variable, not an array. In Java, an array variable declaration must include square brackets ([]) to indicate the variable is an array type. Without brackets, the variable is a primitive or reference type, not an array.

Answer

int[] arr[];

Answer

int[] arr;

Answer

int arr[];

Question 2

Which statement about method overloading with array parameters is true?

Accepted Answer

A method with parameter int[] and another with parameter Integer[] are overloaded.. Method overloading requires methods to have the same name but different parameter lists. int[] and Integer[] are different parameter types (primitive array vs. wrapper class array), so they satisfy the overloading requirement. The return type is irrelevant for overloading.

Answer

A method with parameter int[] and another with parameter int... are overloaded.

Answer

Two methods with the same name and same parameter types but different return types are considered overloaded.

Answer

A method with parameter int[] and another with parameter int[][0] are overloaded.

Question 3

Which two statements about the Arrays class are true? (Choose two.)

Accepted Answer

The Arrays class provides a method to fill an array with a specific value.. Option B is correct because java.util.Arrays provides overloaded static fill() methods (e.g., Arrays.fill(int[] a, int val), Arrays.fill(Object[] a, Object val)) that assign a specified value to every element of an array. Option E is correct because Arrays.asList(T... a) returns a fixed-size List backed by the given array, allowing an array to be viewed as a List. Option A is false because Arrays.sort() is overloaded for both primitive arrays and Object arrays (using natural ordering or a Comparator), not only primitives. Option C is false because binarySearch() requires the array to be sorted and works with primitives or objects, but it is not valid for 'any array' in the sense of unsorted arrays or arrays of incomparable types. Option D is false because Arrays has no deep-copy method; copying is done via System.arraycopy(), clone(), or Arrays.copyOf(), which perform shallow copies for object arrays.

Answer

The Arrays class provides a method to sort only arrays of primitive types.

Answer

The Arrays class provides a method to perform binary search on any array.

Answer

The Arrays class provides a method to deep copy an array.

Question 4

A developer is writing a method to compute the average of an array of scores. The method should handle edge cases gracefully. The scores array may be empty or contain null values if the collection was interrupted. The scores are stored as primitive doubles. Which implementation is safest and follows best practices?

Accepted Answer

public double average(double[] scores) { if (scores == null) return 0.0; double sum = 0; for (double s : scores) sum += s; return scores.length == 0 ? 0.0 : sum / scores.length; }. It explicitly checks for both a null array and an empty array before performing the division. The null check prevents a NullPointerException, and the ternary operator `scores.length == 0 ? 0.0 : sum / scores.length` avoids division by zero when the array is empty. This follows best practices by handling edge cases without relying on exceptions for flow control.

Answer

public double average(double[] scores) { if (scores == null || scores.length == 0) return 0.0; double sum = 0; for (double s : scores) sum += s; return sum / scores.length; }

Answer

public double average(double[] scores) { double sum = 0; for (double s : scores) sum += s; return sum / scores.length; }

Answer

public double average(double[] scores) { try { double sum = 0; for (double s : scores) sum += s; return sum / scores.length; } catch (NullPointerException | ArithmeticException e) { return 0.0; } }

Question 5

A company's legacy code has a method that takes an array of integers and returns a new array containing only the positive numbers. The current implementation uses a fixed-size array equal to the input size and counts positive numbers, then copies them, but if many negatives exist, the result array has trailing zeros (which are removed by copying again). This wastes memory and time. The array can be large (up to 1 million elements). The developer wants to improve memory efficiency and runtime without using external libraries. Which approach should they implement?

Accepted Answer

First count positives, then create an array of that exact size, fill it.. It avoids the overhead of dynamic resizing (as in ArrayList) or boxing (as in streams) by first counting the positives in a single pass, then creating an exact-sized int[] array, and filling it in a second pass. This yields O(n) time complexity and minimal memory overhead, directly addressing the legacy code's inefficiency without external libraries.

Answer

Use an ArrayList to collect positive numbers, then convert to int[].

Answer

Use a stream to filter and collect to array.

Answer

Use a linked list and then convert.

Question 6

A developer writes a method to compute the average of an array of doubles. The method signature is public static double average(double[] values). The developer wants to handle the case where the array is empty by returning 0.0. Which implementation is correct and safe?

Accepted Answer

if (values.length == 0) return 0.0; double sum = 0; for (double v : values) { sum += v; } return sum / values.length;. The method must avoid dividing by zero when the array is empty. An explicit check of values.length == 0 before the loop ensures that an empty array returns 0.0. The enhanced for loop then sums the elements safely, and the division is only performed when the length is non-zero. This approach is both correct and safe for the given scenario.

Answer

double sum = 0; for (double v : values) { sum += v; } return sum / values.length;

Answer

if (values == null || values.length == 0) return 0.0; double sum = 0; for (double v : values) { sum += v; } return sum / values.length;

Answer

double sum = 0; for (int i = 0; i <= values.length; i++) { sum += values[i]; } return sum / values.length;

Question 7

A payroll application must accumulate totals from a variable number of daily pay amounts. A developer writes:

public static double total(double... amounts) {
    double sum = 0;
    for (double a : amounts) { sum += a; }
    return sum;
}

Which two statements about invoking this method are correct? (Choose two.)

Accepted Answer

The call total() compiles and returns 0.0.. A varargs parameter accepts zero or more arguments of the declared type and is implemented as an array, so an empty call yields a zero-length array and summing three doubles works normally. An array of the component type may also be passed directly, whereas a float argument cannot satisfy a double[] requirement.

Answer

The call total(5.0, 6.0f, 7.0) compiles because numeric arguments are widened automatically.

Answer

The call total(new double[]{1.0, 2.0}) is rejected because varargs only accepts individual values.

Answer

The call total(null) always throws a NullPointerException at runtime.

Question 8

A developer is reviewing a method that is supposed to return the largest value in an int array. The method is declared as public static int findMax(int[] numbers). The array may be empty. Which implementation correctly handles all valid inputs without throwing an exception?

Accepted Answer

if (numbers.length == 0) throw new IllegalArgumentException("Empty array"); int max = numbers[0]; for (int i = 1; i < numbers.length; i++) { if (numbers[i] > max) max = numbers[i]; } return max;. The method must not index an empty array. Checking the length first and throwing a documented exception for the empty case, then initializing the maximum with the first element, avoids ArrayIndexOutOfBoundsException and handles negative values correctly. Using a sentinel like 0 or Integer.MIN_VALUE can produce incorrect results for empty or all-negative arrays.

Answer

int max = 0; for (int n : numbers) { if (n > max) max = n; } return max;

Answer

int max = numbers[0]; for (int i = 1; i < numbers.length; i++) { if (numbers[i] > max) max = numbers[i]; } return max;

Answer

int max = Integer.MIN_VALUE; for (int n : numbers) { if (n > max) max = n; } return max;

Question 9

A developer is writing overloaded methods that operate on arrays and needs to understand how the Java compiler resolves overloaded calls involving array parameters. Which two statements are correct? (Choose two.)

Accepted Answer

When both an exact array parameter method and a varargs method are applicable, the fixed-arity array method is preferred. Overloading is determined by the parameter list, encompassing parameter types and their order, so array and non-array parameters can distinguish methods. During resolution the compiler favors a match that needs no varargs conversion, meaning an exact array parameter is chosen over an equivalent varargs signature when both are applicable to the same call.

Answer

A call passing an int array to a method declared as int... is always a compile-time error

Answer

Two overloaded methods in the same class may differ only by return type

Answer

Overloaded methods must have the same number of parameters to be legal

Question 10

A developer writes a method that takes an int array and returns the sum of its elements. The method signature is: 'public static int sumArray(int[] arr)'. Which statement correctly calls this method?

Accepted Answer

int result = sumArray(new int[]{1,2,3});. It uses the correct syntax for creating and passing an anonymous int array to the sumArray method. The expression `new int[]{1,2,3}` creates an int array object with the specified elements, which matches the method's parameter type `int[]`. The method then returns the sum, which is assigned to the int variable `result`.

Answer

int result = sumArray(true);

Answer

int result = sumArray([1,2,3]);

Answer

int result = sumArray(5);

Question 11

Given the code snippet: 'int[] nums = {10, 20, 30, 40}; int sum = 0; for (int i = 0; i < nums.length; i++) { sum += nums[i]; }'. What is the value of sum after execution?

Accepted Answer

100. (100) because the for loop iterates over each element of the array {10, 20, 30, 40} and adds it to the sum variable. The sum starts at 0, and after adding 10, 20, 30, and 40, the total becomes 100.

Answer

30

Answer

60

Answer

140

Question 12

A method 'public static void modifyArray(int[] arr) { arr[0] = 99; }' is called with 'int[] myArray = {1,2,3}; modifyArray(myArray); System.out.println(myArray[0]);'. What is the output?

Accepted Answer

99. In Java, when an array is passed to a method, the reference is passed by value. The method receives a copy of the reference, but both references point to the same array object. Therefore, modifying an element inside the method changes the original array. After the call, myArray[0] is 99.

Answer

1

Answer

0

Answer

Compilation error