1Z0-811 Practice Test 16 — 15 Questions

Question 1

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 2

A developer is working on a Java application that processes user input. The application reads a string from the console and needs to compare it with a predefined constant string "ADMIN". The developer writes the following code: if (input == "ADMIN") { grantAccess(); }. During testing, the condition sometimes fails even when the user enters ADMIN. The input string is obtained via Scanner.nextLine(). Which is the most likely cause and best fix?

Accepted Answer

Use input.equals("ADMIN") instead of ==.. `==` compares object references, not string content. `Scanner.nextLine()` returns a new `String` object, so `input == "ADMIN"` compares references, which are different even if the content matches. Using `input.equals("ADMIN")` compares the actual character sequence, which is the correct way to test string equality in Java.

Answer

Use input.compareTo("ADMIN") == 0.

Answer

Use input == "ADMIN" with intern() on input.

Answer

Convert input to char array and compare.

Question 3

A method is declared as:
public void setAge(int age) { this.age = age; }
Which statement is correct about this code assuming the class has an instance variable age?

Accepted Answer

The method sets the instance variable age.. The method `setAge(int age)` uses the `this` keyword to assign the parameter value to the instance variable `age`, which is a standard setter pattern in Java. The method has a `void` return type and is not a constructor, and it compiles successfully because the instance variable `age` is assumed to exist in the class.

Answer

The method is a constructor.

Answer

The method will cause a compilation error.

Answer

The method is static.

Question 4

A team decides to use a single Java source file for a small application. Which statement is true about the file structure?

Accepted Answer

It can contain exactly one public class with the same name as the file.. In Java, when a source file contains a public class, the file name must exactly match the public class name, including case sensitivity. This is a fundamental rule enforced by the Java compiler to ensure proper class loading and package structure. The file can have at most one public top-level class, and that class name determines the file name.

Answer

It must have a main method to compile.

Answer

It can contain multiple public classes.

Answer

The public class name can differ from the file name.

Question 5

Which primitive data type should be used to store a single character?

Accepted Answer

char. The `char` primitive data type in Java is specifically designed to store a single 16-bit Unicode character, ranging from '\u0000' (0) to '\uffff' (65,535). It can represent any character in the Unicode standard, including letters, digits, and symbols, making it the appropriate choice for a single character value.

Answer

int

Answer

byte

Answer

String

Question 6

Which method overloading is valid?

Accepted Answer

void print(int a) and void print(String s) {}. Method overloading in Java requires methods to have the same name but different parameter lists (different number, type, or order of parameters). Here, `void print(int a)` and `void print(String s)` have different parameter types (`int` vs `String`), which satisfies the overloading rule. The return type or access modifiers do not affect overloading.

Answer

void print(int a) and void print(int b) {}

Answer

void print(int a) and int print(int a) {}

Answer

void print(int a) and private void print(int a) {}

Question 7

Which TWO are best practices for using control flow statements? (Choose two.)

Accepted Answer

Use the enhanced for loop instead of the traditional for loop when iterating over arrays.. Option A is correct because the enhanced for loop (for-each) eliminates the index variable and off-by-one errors, making iteration over arrays and Iterable collections clearer and less error-prone when the index itself is not needed. Option B is correct because a break statement provides a clean, readable way to terminate a loop as soon as its exit condition is satisfied, avoiding unnecessary iterations and often simplifying loop logic. Option C is not a best practice since deeply nested if-else blocks hurt readability and maintainability; guard clauses or early returns are preferred. Option D is wrong because switch statements are generally clearer and more efficient than long else-if chains for multi-way branching on a single value. Option E is wrong because Java has no goto statement (it is a reserved but unused keyword), and labeled break is the proper construct for exiting nested loops.

Answer

Use deeply nested if-else blocks to handle all possible conditions.

Answer

Prefer multiple else-if chains over switch statements for multi-way branches.

Answer

Use a goto statement to jump out of nested loops.

Question 8

In a banking application, a class 'Account' has private field 'balance' and public methods 'getBalance()' and 'setBalance(double)'. This is an example of which OOP principle?

Accepted Answer

Encapsulation. Encapsulation is the correct answer (D) because the private field 'balance' is hidden from direct external access and can only be read or modified through the public methods getBalance() and setBalance(double), which control how the data is accessed. This bundling of data with methods that operate on it, while restricting direct access to the internal state, is the defining characteristic of encapsulation. Abstraction (A) is about exposing only essential behavior and hiding implementation complexity, which is related but not the specific mechanism shown here. Inheritance (B) involves deriving a class from a parent class to reuse or extend behavior, and polymorphism (C) involves treating objects of different types through a common interface, neither of which is demonstrated by private fields with public accessors.

Answer

Abstraction

Answer

Inheritance

Answer

Polymorphism

Question 9

Refer to the exhibit. What is the result?

Accepted Answer

Runtime exception. The code attempts to divide an integer by zero, which in Java throws an ArithmeticException at runtime. Since the division is performed with integer operands (int / int), Java does not allow division by zero and raises an exception, not a floating-point infinity or zero. Therefore, the correct answer is C: Runtime exception.

Answer

Compilation error

Answer

0

Answer

Infinity

Question 10

Which THREE are valid Java identifiers?

Accepted Answer

my_value. Option B, my_value, is a valid Java identifier because it begins with a letter and contains only letters and the underscore character, which are legal identifier parts. Option C, $dollar, is valid because the dollar sign ($) is explicitly allowed as a Java identifier start character (and as a subsequent character). Option E, _myVar, is valid because the underscore (_) is a legal Java identifier start character, so an identifier may begin with it. Option A, 2ndValue, is invalid because a Java identifier cannot begin with a digit. Option D, my-var, is invalid because the hyphen (-) is not a legal character in a Java identifier; only letters, digits, $, and _ are permitted.

Answer

2ndValue

Answer

my-var

Question 11

Match each Java term to its correct definition.

Accepted Answer

JDK: Software development kit that includes tools for compiling, debugging, and running Java programs. Correct matches: JDK is the development kit; JRE is the runtime; JVM executes bytecode; bytecode is the intermediate format. Common confusions: mixing JDK and JRE or JVM with JDK.

Answer

JDK: Runtime environment that includes the JVM and core libraries required to run Java programs

Answer

JVM: Software development kit that includes tools for compiling, debugging, and running Java programs

Question 12

A team is developing a large-scale e-commerce platform using Java. They have a class hierarchy: Product (abstract), Electronics, Clothing, Food. Each product has a discount method that applies different logic. The team notices that whenever a new product type is added, they must modify the existing discount calculation logic in multiple places, leading to high maintenance costs. They want to refactor to follow the Open/Closed Principle. Which approach should they take?

Accepted Answer

Define an interface Discountable with a method calculateDiscount() and have each product class implement it. Option A is correct because defining a Discountable interface with calculateDiscount() and having each concrete product class (Electronics, Clothing, Food) implement it lets new product types add their own discount logic without modifying existing code, which is exactly the Open/Closed Principle (open for extension, closed for modification). Polymorphism dispatches calculateDiscount() to the appropriate subclass at runtime, so the existing discount calculation logic remains untouched when a new product type is introduced. Option B violates OCP because a single Product method with if-else type checks must be edited every time a new product type is added. Option C is wrong because reflection-based external handling is fragile, bypasses type safety, and still requires changes to the external handler for new types. Option D is wrong because a switch statement in a utility class centralizes type checks and must also be modified whenever a new product type appears.

Answer

Create a single discount method in Product that uses if-else checks on type

Answer

Remove the discount method and handle it externally using reflection

Answer

Use a switch statement in a utility class to handle all product types

Question 13

In a Java application, a class 'OrderProcessor' contains a method that processes orders. The method currently handles multiple responsibilities: validating order data, calculating totals, updating inventory, and sending notifications. The team wants to refactor this method to follow the Single Responsibility Principle. Which action should they take?

Accepted Answer

Create separate classes or methods for each responsibility and compose them in OrderProcessor. The Single Responsibility Principle (SRP) states that a class or method should have only one reason to change. The current method mixes validation, calculation, inventory updates, and notifications — four distinct concerns. The correct refactor is to extract each responsibility into its own class or method and have OrderProcessor compose them, so each unit has a single axis of change.

Answer

Use a single utility method that uses if-else for each case

Answer

Override the method in subclasses for each responsibility

Answer

Merge all responsibilities into a superclass

Question 14

A developer needs a loop that executes its body at least once, then repeats only while a boolean condition remains true. Which loop construct should the developer choose?

Accepted Answer

do-while loop. Only the do-while loop checks its condition after the body, guaranteeing at least one execution. The while and for loops check before the first iteration, and the enhanced for loop depends on the size of the collection. When a body must run once and then repeat conditionally, do-while is the direct match.

Answer

while loop

Answer

for loop

Answer

enhanced for loop

Question 15

Given the following Java code:

```java
public class Main {
    public static void main(String[] args) {
        int a = 10, b = 5, c = 15;
        int result = (a > b) ? (a > c) ? a : c : (b > c) ? b : c;
        System.out.println(result == 15 ? "Yes" : "No");
    }
}
```

What is the output?

Accepted Answer

Yes. Yes, because the nested ternary expression evaluates as follows: (a > b) is true (10 > 5), so the expression proceeds to the true branch (a > c) ? a : c. Since a > c is false (10 > 15 is false), this inner ternary returns c, which is 15. The comparison result == 15 is therefore true, so the outer ternary prints "Yes". The other options do not fit: the code compiles without error, no runtime exception occurs, and the output is not "No".

Answer

Compilation fails

Answer

No

Answer

Runtime error