1Z0-811 Timed Practice Test 2 — 10 Questions

Question 1

A logistics application needs to store a shipment's unique tracking code, which is a fixed 12-character alphanumeric identifier. The code must not be modified after it is assigned. Which Java type is the most appropriate to declare for storing this tracking code?

10 minute time limit — choose an answer to begin.

Accepted Answer

String. A tracking code is a sequence of characters that must remain unchanged after assignment. String is the only offered type that can hold multiple characters and is immutable by design, so it satisfies both the storage and the no-modification requirement. The other types either hold a single character, a number, or a truth value, none of which can represent the code.

Answer

boolean

Answer

char

Answer

int

Question 2

Which of the following best demonstrates polymorphism in Java?

Accepted Answer

Using an interface reference to call a method on an implementing object. Polymorphism in Java allows an object to take multiple forms, typically achieved through inheritance and interfaces. Option B demonstrates this by using an interface reference to invoke a method on an implementing object, where the actual method executed is determined at runtime based on the object's class, not the reference type.

Answer

Overloading a method with different parameter lists

Answer

Using static methods

Answer

Overriding a method in a subclass

Answer

Using final methods

Question 3

Which three of the following are valid ways to declare and initialize a variable of type int? (Choose three.)

Accepted Answer

int b = 0xA;. Option A (int b = 0xA;) is valid because Java supports hexadecimal integer literals prefixed with 0x, and 0xA equals decimal 10, which fits in an int. Option C (int d = 010;) is valid because a leading zero denotes an octal literal, and 010 is octal for decimal 8, a legal int value. Option E (int a = 10;) is valid because 10 is a standard decimal int literal assigned directly to an int variable. Option B (int e = 10.0;) is invalid because 10.0 is a double literal and cannot be assigned to an int without an explicit cast. Option D (int c = 0b2;) is invalid because the 0b prefix denotes a binary literal, and the digit 2 is not permitted in binary.

Answer

int e = 10.0;

Answer

int c = 0b2;

Question 4

A Java class named 'Helper' is defined in package 'utils'. Another class in a different package tries to access a public method of Helper but receives a compilation error. The Helper class is declared as 'class Helper' (without public modifier). What is the likely issue?

Accepted Answer

The class has package-private access. In Java, a class without an access modifier (i.e., 'class Helper') has package-private (default) access, meaning it is only accessible within its own package. Since the other class is in a different package, it cannot access the Helper class at all, even if its methods are public. The compilation error occurs because the class itself is not visible.

Answer

The method is declared as final

Answer

The method is not static

Answer

The class is abstract

Question 5

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.

Answer

0

Answer

5

Answer

Compilation error

Question 6

During execution, the JVM uses Just-In-Time (JIT) compilation. What is its primary benefit?

Accepted Answer

Improves execution speed by compiling frequently used bytecode to native code.. JIT compilation improves execution speed by compiling frequently used bytecode into native machine code at runtime. Option A is incorrect because JIT does not translate bytecode into an intermediate language; it compiles to native code. Option C is incorrect because JIT compiles bytecode, not source code. Option D is incorrect because JIT's primary purpose is performance, not security.

Answer

Translates bytecode into an intermediate language for interpretation.

Answer

Converts Java source code directly into bytecode.

Answer

Enhances security by verifying bytecode integrity.

Question 7

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.

Answer

Use parallel streams to perform the search in parallel.

Answer

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

Answer

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

Question 8

Match each Java tool to its function.

Accepted Answer

javac: Compiles Java source code into bytecode. The correct matches are: javac compiles source code, java runs applications, javadoc generates documentation, and jar creates archives. Common confusions involve mixing up javac with jar and java with javadoc.

Answer

javac: Packages class files into an archive

Answer

java: Generates API documentation

Question 9

Which loop construct guarantees that the loop body executes at least once?

Accepted Answer

do-while loop. The do-while loop is the only Java loop construct that guarantees the loop body executes at least once because the condition is evaluated after the body executes. In contrast, the while and for loops evaluate the condition before the first iteration, so the body may never execute if the condition is initially false. The enhanced for loop also checks for elements before entering the body.

Answer

Enhanced for loop

Answer

while loop

Answer

for loop

Question 10

Which TWO methods correctly modify the passed array in place?

Accepted Answer

public void zeroOut(int[] a) { for (int i = 0; i < a.length; i++) a[i] = 0; }. It directly modifies each element of the passed array by assigning 0 to a[i] within the loop. In Java, when an array is passed to a method, the method receives a reference to the same array object, so changes to the array's elements are reflected in the caller's array.

Answer

public void reset(int[] a) { a = new int[10]; }

Answer

public void swap(int[] a) { int[] temp = a; a = new int[1]; a[0] = temp[0]; }

Answer

public void setFirst(int[][] a) { a = new int[1][1]; a[0][0] = 5; }