1Z0-811 Arrays and Methods Practice Test 5 — 15 Questions

Question 1

Which two statements about passing arrays to methods are correct? (Select two.)

Accepted Answer

Modifying the array elements inside the method affects the original array.. In Java, arrays are objects, and when you pass an array to a method, you pass a copy of the reference to the array. This means the method can modify the contents of the array (e.g., change element values), and those changes are reflected in the original array because both the caller and the method refer to the same array object in heap memory.

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Passing an array is the same as passing each element individually.

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The method can change the size of the original array.

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If the method assigns a new array to the parameter, the original reference is updated outside the method.

Question 2

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.

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int[] arr[];

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int[] arr;

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int arr[];

Question 3

Given the method: public static void modify(int[] data) { data = new int[]{10,20}; } What is the output of: int[] vals = {1,2}; modify(vals); System.out.println(vals[0]);

Accepted Answer

1. In Java, when an object reference (including an array) is passed to a method, the reference itself is passed by value. Inside `modify`, the assignment `data = new int[]{10,20}` reassigns the local variable `data` to a new array object, but this does not affect the original reference `vals` in the caller. Therefore, `vals[0]` remains `1`, making option C correct.

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10

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Compilation error

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0

Question 4

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.

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

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

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

Question 5

A developer writes a method that accepts an array and returns the sum of all elements. Which implementation is correct if the array might be null?

Accepted Answer

public int sum(int[] arr) { if (arr == null) return 0; int s=0; for (int n:arr) s+=n; return s; }. It explicitly checks for a null array before attempting to access its length or iterate over its elements. In Java, accessing `arr.length` or using an enhanced for loop on a null reference throws a `NullPointerException`. By returning 0 for null input, the method gracefully handles the edge case without crashing.

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public int sum(int[] arr) { if (arr.length==0) return 0; int s=0; for (int n:arr) s+=n; return s; }

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public int sum(int[] arr) { try { int s=0; for (int n:arr) s+=n; return s; } catch(NullPointerException e) { return -1; } }

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public int sum(int[] arr) { int s=0; for (int n:arr) s+=n; return s; }

Question 6

What is the result of the following code? int[] arr = new int[3]; arr[3] = 5; System.out.println(arr[3]);

Accepted Answer

Runtime exception. The code attempts to access index 3 of an array of length 3. Since Java arrays are zero-indexed, valid indices are 0, 1, and 2. Accessing index 3 throws an ArrayIndexOutOfBoundsException at runtime, so option A is correct.

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0

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5

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Compilation error

Question 7

A developer wants to sort an array of primitive ints in descending order. Which approach will work without using third-party libraries?

Accepted Answer

Arrays.sort(arr); // then reverse the array manually. `Arrays.sort(int[])` sorts the array in ascending order, and then manually reversing the array yields descending order. The other options fail because `Arrays.parallelSort()` also sorts ascending, `Collections.reverseOrder()` requires an array of objects (not primitives), and a custom comparator cannot be used with primitive arrays in Java.

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Arrays.parallelSort(arr);

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Arrays.sort(arr, Collections.reverseOrder());

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Arrays.sort(arr, (a,b) -> b - a);

Question 8

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.. The `Arrays.fill()` method allows you to assign a specific value to every element of an array, or to a specified range within the array. This is a static utility method provided by the `java.util.Arrays` class, and it works for both primitive and object arrays.

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

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

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

Question 9

Which two statements about method parameter passing in Java are true? (Choose two.)

Accepted Answer

When a primitive type is passed to a method, a copy of the value is passed.. Java always passes primitive types (like int, double, boolean) by value, meaning a copy of the actual value is made and passed into the method. Any modifications to the parameter inside the method affect only the copy, not the original variable in the caller.

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When an array is passed to a method, changes to the array elements inside the method are not reflected in the caller.

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When an array is reassigned inside a method, the original array in the caller is also reassigned.

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When a String is passed to a method, the method can modify the original String.

Question 10

Which three statements about arrays are correct? (Choose three.)

Accepted Answer

Arrays are objects in Java.. In Java, arrays are objects that are dynamically created and can be assigned to variables of type Object, cloned via the clone() method, and have a length field (not a method). They inherit from java.lang.Object and are treated as reference types, even when they store primitive values.

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The size of an array can change after creation.

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The length of an array must be specified at compile time with a constant expression.

Question 11

A company manages employee data stored in an array of Employee objects. The HR application frequently needs to find an employee by ID. The current implementation uses a linear search through the array each time. Performance reports indicate that this search is becoming a bottleneck as the company grows. The array is not sorted, and the company does not want to sort it because the order is meaningful for display. The array is large and frequently updated. The development team considers several options to improve the search performance without changing the array order. Which approach should they implement?

Accepted Answer

Create a HashMap that maps IDs to Employee objects, and maintain it alongside the array.. The best choice because using a HashMap provides O(1) average-time lookups, which is far superior to linear search. The HashMap can be maintained alongside the array without disturbing the array order, as updates to the array are reflected in the HashMap. Option B (parallel streams) still performs a linear search (O(n)) and adds overhead for parallelization, so it does not solve the bottleneck. Option C (HashSet of IDs) only allows checking existence but does not provide the Employee object; you would still need to search the array to retrieve the Employee, so it does not reduce complexity. Option D (binary search on a sorted copy) requires O(n log n) time to sort a copy for each search, which is even worse than linear search.

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Use parallel streams to perform the search in parallel.

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Convert the array to a HashSet of employee IDs and use contains() to check existence.

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Use Arrays.binarySearch() on the array after temporarily sorting a copy each time.

Question 12

A team is developing a financial application that processes large arrays of market data. They have a method that calculates moving averages by copying a subarray for each window. The current implementation creates a new array for each window using System.arraycopy. The application is running slowly in production. The team identifies that the method is called millions of times per minute. The array is large and the window size is small. The garbage collector overhead is high due to many short-lived arrays. Which optimization should they apply to reduce object creation and improve performance?

Accepted Answer

Use a single temporary array and reuse it by copying data into it for each window.. Reusing a single temporary array eliminates the repeated allocation of short-lived arrays for each window, directly reducing garbage collector overhead. The current implementation uses System.arraycopy to create a new array per window, which is the primary source of object churn. By allocating one array once and copying data into it for each window, the team minimizes object creation while still performing the necessary copy operation.

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Use a Stream to process the array without creating intermediate arrays.

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Use Arrays.copyOfRange() which is faster than System.arraycopy.

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Use ArrayList instead of array to avoid copy.