1Z0-811 Arrays and Methods — 50 Questions

Question 1

A method 'public static int findMax(int[] numbers)' returns the maximum value in the array. Which implementation correctly handles an empty array by returning 0?

Accepted Answer

if(numbers.length == 0) return 0; int max = numbers[0]; for(int i=1; i<numbers.length; i++) if(numbers[i] > max) max = numbers[i]; return max;. Ly handles an empty array by checking `numbers.length == 0` and returning 0 before attempting to access `numbers[0]`, which would throw an `ArrayIndexOutOfBoundsException` on an empty array. It then initializes `max` to the first element and iterates from index 1, ensuring all elements are compared correctly even if all numbers are negative.

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

if(numbers.length == 0) return 0; int max = 0; for(int n: numbers) if(n > max) max = n; return max;

Question 2

Which THREE statements are correct about the 'main' method signature in Java?

Accepted Answer

It must be declared public.. Option A is correct because the JVM launcher requires the entry-point method to be public so it can be invoked from outside the class. Option C is correct because the main method must be declared void; the JVM does not use a return value from it. Option D is correct because main must be static so the JVM can call it without instantiating the class. Option B is incorrect because a main method returning int is not recognized as the standard entry point. Option E is incorrect because the method must be named exactly main, not any valid identifier.

Answer

It can be declared to return an int.

Answer

It can be named any valid identifier.

Question 3

Match each control flow statement to its purpose.

Accepted Answer

if-else: Executes a block of code based on a boolean condition.. The correct matches are: if-else (A) executes based on condition, switch (B) selects based on value, for loop (C) repeats fixed times, while loop (D) repeats while condition true. Options E and F are incorrect because they misassign the purposes.

Answer

if-else: Repeats a block of code a fixed number of times.

Answer

switch: Repeats a block of code as long as a condition is true.

Question 4

A method is designed to compute the average of an array of test scores. What should the method return if the array is empty (length 0)?

Accepted Answer

Return 0.0. The method should return 0.0 for an empty array to avoid division by zero and to provide a safe default value. In Java, an empty array has length 0, and computing the average would require dividing by zero, which throws an ArithmeticException. Returning 0.0 is a common convention for empty collections, as it allows the caller to handle the result gracefully without crashing.

Answer

Do not compile; requires a return of type double

Answer

Throw a RuntimeException

Answer

Return null

Question 5

An application requires storing a fixed set of 12 monthly temperatures. Which initialization is most appropriate?

Accepted Answer

double[] temps = {15.5, 16.2, 18.0, 20.1, 23.4, 27.8, 30.0, 29.5, 26.2, 22.0, 18.5, 16.0};. It initializes a fixed-size array of 12 doubles with the actual monthly temperature values in a single statement, which is the most appropriate for storing a fixed set of 12 values. The array size is implicitly determined by the number of elements in the initializer list, and the syntax is concise and readable for this use case.

Answer

ArrayList temps = new ArrayList<>();

Answer

double[] temps = new double[12];

Answer

double temps[] = {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0};

Question 6

A method is declared as: public static int[] generateSequence(int n) { ... }. Which return statement is valid inside this method?

Accepted Answer

return new int[n];. The method's return type is `int[]`, meaning it must return a reference to an integer array. Option B, `return new int[n];`, creates an array of length `n` and returns it, which is valid. Option D, `return new int[0];`, also creates an integer array (of length 0) and returns it, which is syntactically valid as well. Options A and C are invalid because they return primitive `int` values, not `int[]` references. Therefore, both B and D are correct return statements.

Answer

return result; where result is an int variable

Answer

return 0;

Question 7

A programmer writes code to transpose a 2D array (matrix). Given: int[][] matrix = {{1,2},{3,4}}; int[][] result = new int[2][2]; for (int i=0; i<2; i++) for (int j=0; j<2; j++) result[j][i] = matrix[i][j]; What is the value of result[1][0]?

Accepted Answer

2. The code transposes the matrix by assigning matrix[i][j] to result[j][i]. For result[1][0], we need the value where j=1 and i=0, which comes from matrix[0][1] = 2. Thus, result[1][0] = 2, making option C correct.

Answer

4

Answer

3

Answer

1

Question 8

What is printed when the main method runs?

Accepted Answer

5. The method `modifyArray` receives a reference to the array, and the assignment `arr = new int[]{100};` changes the local reference `arr` to point to a new array object. The original array in `main` remains unchanged, so `arr[0]` still prints 5. Java passes object references by value, meaning the reference itself is copied, and reassigning the local reference does not affect the caller's reference.

Answer

0

Answer

Compilation error: cannot assign new array to parameter

Answer

100

Question 9

Which method invocation is ambiguous given these overloaded methods? public void process(int[] a) and public void process(int... a)

Accepted Answer

process(new int[]{1, 2});. When you call process(new int[]{1, 2}), the compiler cannot determine whether to use the method with an int[] parameter or the varargs method (int... a). Both methods have the same signature after type erasure, and the argument is an int array, which matches both exactly, causing an ambiguity error.

Answer

process(1, 2);

Answer

process((int[]) null);

Answer

process();

Question 10

Which TWO are valid ways to declare and initialize an array of Strings?

Accepted Answer

String[] names = new String[]{"A", "B"};. Option C is correct because it uses the explicit array creation expression `new String[]{"A", "B"}`, which is a fully valid way to declare and initialize a String array with the two elements "A" and "B". Option E is correct because `String names[] = {"A", "B"};` uses the legal C-style bracket placement on the variable name and the array initializer shorthand, which the compiler accepts for a String array. Option A is invalid because the trailing `[]` after the initializer `{"A", "B"}[]` is not valid Java syntax. Option B is invalid as an initialization to specific values because `new String[2]` only creates an array of length 2 with null elements, not the strings "A" and "B". Option D is invalid because `{1, 2}` contains int literals, which cannot be assigned to a String[] array.

Answer

String[] names = {"A", "B"}[];

Answer

String names[] = new String[2];

Answer

String[] names = {1, 2};

Question 11

Refer to the exhibit. What is the output?

Accepted Answer

2. The code initializes an array `arr` with values {1, 2, 3}. The for loop iterates over the array, and the `if` condition checks if the current element equals 2. When `arr[1]` (value 2) is encountered, the `break` statement exits the loop immediately. The loop executes only twice (for indices 0 and 1), so the counter `count` is incremented twice, resulting in output 2.

Answer

3

Answer

1

Answer

0

Question 12

Refer to the exhibit. The code at line 6 of ArrayExample.java is: int[] arr = {10, 20, 30, 40, 50}; int sum = 0; for (int i = 0; i <= arr.length; i++) sum += arr[i]; Which change fixes the exception?

Accepted Answer

Change loop condition to i < arr.length. The exception occurs because the loop condition `i <= arr.length` causes the loop to iterate one index beyond the array's last valid index (arr.length - 1). When `i` equals `arr.length` (5), `arr[5]` is accessed, which throws an ArrayIndexOutOfBoundsException. Changing the condition to `i < arr.length` ensures the loop runs only for indices 0 through 4, fixing the exception. Option D, changing `arr.length` to `arr.length - 1` in the condition, also technically fixes the exception, but it is not the standard or recommended fix; the intended correct answer is to use the `<` operator.

Answer

Change array declaration to int[] arr = new int[6];

Answer

Change loop initialization to i = 1

Question 13

Which two of the following are valid ways to declare and initialize an array of integers? (Select two.)

Accepted Answer

int[] arr = new int[5];. Option B, `int[] arr = new int[5];`, is valid because it declares an int array and uses the `new` keyword with a size specifier to allocate five elements, which are automatically initialized to 0. Option D, `int arr[] = new int[]{1, 2};`, is valid because C# permits the array brackets to appear after the variable name, and the `new int[]{1, 2}` syntax uses an implicitly sized array initializer to create and populate a two-element array. Option A is invalid because you cannot combine an explicit size (`new int[5]`) with an array initializer list in that form. Option C is invalid because the size specifier `5` cannot appear in the type declaration (`int[5] arr;`). Option E is invalid because it attempts to assign an int array to a scalar `int` variable rather than declaring an array type.

Answer

int[] arr = new int[5]{1, 2, 3, 4, 5};

Answer

int[5] arr;

Answer

int arr = new int[5];

Question 14

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 15

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 16

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 17

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 18

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 19

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 20

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.