1Z0-811 Practice Test 34 — 15 Questions

Question 1

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.

Answer

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

Answer

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

Answer

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

Question 2

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.

Answer

10

Answer

Compilation error

Answer

0

Question 3

Which of the following scenarios demonstrates the most appropriate use of a continue statement?

Accepted Answer

Skipping the current iteration and moving to the next when a condition is met. The `continue` statement in Java is specifically designed to skip the remaining code in the current iteration of a loop and proceed directly to the next iteration. This is the most appropriate use case, as it allows you to bypass certain iterations based on a condition without breaking out of the loop entirely.

Answer

Restarting the loop from the beginning

Answer

Implementing fall-through in a switch statement

Answer

Exiting a loop early when a condition is met

Question 4

A developer wants to achieve loose coupling between components. Which two practices support loose coupling? (Choose two.)

Accepted Answer

Using interfaces to define contracts. Loose coupling is promoted by coding to interfaces and favoring composition over inheritance, as both reduce dependency on concrete implementations.

Answer

Using inheritance to share implementation

Answer

Using private fields with public getters

Answer

Using static methods extensively

Question 5

Which two of the following are fundamental principles of Object-Oriented Programming? (Choose two.)

Accepted Answer

Encapsulation. The four main OOP principles are encapsulation, inheritance, polymorphism, and abstraction.

Answer

Iteration

Answer

Compilation

Answer

Synchronization

Question 6

Which THREE of the following expressions compile without error? (Choose 3)

Accepted Answer

byte b = 1 + 2;. Options A, C, D are correct. A: byte addition promoted to int, then assigned to byte requires explicit cast? Actually byte + byte = int, but assignment to byte will require explicit cast. Wait: byte b = 1+2? 1 and 2 are literals, compile-time constant, so assignment is allowed because constant expression. Actually 1 and 2 are int literals, but the result is compile-time constant 3, which fits in byte, so it's allowed. So A compiles. B: int + long = long, assigning to int requires explicit cast, so compile error. C: double d = 10; 10 is int, widening assignment to double is fine. D: boolean b = (false || true); boolean expression, fine. E: float f = 5.5; 5.5 is double by default, requires explicit cast or f suffix, so compile error. So correct: A, C, D.

Answer

int i = 5L + 10;

Answer

float f = 5.5;

Question 7

A junior developer writes a method that attempts to modify a String: public void update() { String s = "Hello"; s.concat(" World"); System.out.println(s); } What will be printed when update() is called?

Accepted Answer

Hello. Strings are immutable in Java. The concat() method returns a new String but the original object remains unchanged because the result is not assigned.

Answer

Hello World

Answer

Hello World (no space)

Answer

Compilation error

Question 8

A class that does not define any constructor has:

Accepted Answer

A default no-argument constructor. Java automatically provides a default no-arg constructor with the same access as the class.

Answer

A private constructor

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A public constructor with arguments

Answer

It cannot be instantiated

Answer

No constructor

Question 9

Which primitive type can store a single character?

Accepted Answer

char. char is the primitive for a single 16-bit Unicode character.

Answer

String

Answer

int

Answer

Character

Question 10

Refer to the exhibit.

What is the output?

Accepted Answer

Vehicle. In Java, fields are not polymorphic; the reference type determines which field is accessed. v is of type Vehicle, so v.type refers to Vehicle's type field.

Answer

null

Answer

Compilation error

Answer

Car

Answer

Runtime error

Question 11

Refer to the exhibit. What is the potential issue with this singleton implementation in a multithreaded environment?

Accepted Answer

Not thread-safe; two threads could simultaneously create different instances. The if-check and instantiation are not atomic. Two threads could both see instance == null and create separate instances, violating the singleton guarantee.

Answer

The getInstance() method should be non-static

Answer

Compilation error because the constructor is private

Answer

Memory leak because instances are never garbage collected

Question 12

What is the value of 10 % 3?

Accepted Answer

1. The % operator returns remainder of division. 10 divided by 3 is 3 with remainder 1.

Answer

0

Answer

1.0

Answer

3

Question 13

A developer writes a class 'Animal' with a method 'sound()'. The 'Cat' subclass overrides 'sound()'. If an Animal reference points to a Cat object, which method is called when sound() is invoked?

Accepted Answer

Cat's sound(). Polymorphism ensures that the overridden method in the actual object's class is called at runtime, even if the reference is of the superclass type.

Answer

Runtime error

Answer

Animal's sound()

Answer

Compilation error

Question 14

A security-sensitive class should not be extended by any other class. Which modifier should be applied to the class declaration?

Accepted Answer

final. The final modifier prevents a class from being subclassed, which is appropriate for security or design reasons.

Answer

abstract

Answer

static

Answer

private

Question 15

Which TWO of the following are valid Java identifiers? (Choose two.)

Accepted Answer

$value. In Java, identifiers must start with a letter, underscore, or dollar sign, and subsequent characters can include digits. Reserved words cannot be used. _myVariable and $value are valid. 2ndPlace starts with a digit, my-var contains a hyphen, and class is a reserved word.

Answer

my-var

Answer

2ndPlace

Answer

class