Java SE 11 Developer Free Practice Test — 30 Questions

Question 1

In a multi-threaded application, a developer is implementing a feature that requires a method to be called multiple times within itself, each time needing to acquire a lock to ensure thread safety. The developer decides to use ReentrantLock for this purpose. What is the primary advantage of using ReentrantLock in this scenario compared to traditional synchronized blocks?

Accepted Answer

It allows the same thread to acquire the lock multiple times without causing a deadlock.

Question 2

In a software development project, a developer decides to use the `var` keyword for local variable declarations to enhance code readability. However, they encounter a situation where the inferred type of a variable is not immediately clear to other team members reviewing the code. Which of the following statements best describes the implications of using `var` in this context?

Accepted Answer

Using `var` can lead to ambiguity in type inference, potentially making the code less understandable for others who may not be familiar with the context.

Question 3

A retail company has a list of products, each represented by a `Product` object containing attributes like `name`, `category`, and `sales`. The company wants to identify products with sales greater than 1000 units and collect their names into a new list. Which combination of operations should the company use to achieve this efficiently?

Accepted Answer

Use `stream().filter(p -> p.getSales() > 1000).map(Product::getName).collect(Collectors.toList())`

Question 4

A software development project utilizing the Java Development Kit (JDK) incurs a fixed cost of $C_f = 5000$ and a variable cost of $C_v = 150$ per hour. If the total number of hours worked on the project is $h = 40$, what is the total cost $C_{total}$ of the project?

Accepted Answer

$11000$

Question 5

In a scenario where a developer is tasked with reading a large text file containing user data, which approach would be the most efficient and appropriate for handling the file\'s content while ensuring proper character encoding and performance optimization?

Accepted Answer

Utilize a BufferedReader wrapped around a FileReader to read the file line by line, ensuring efficient memory usage and proper character encoding.

Question 6

A software engineer is refactoring a legacy Java application into a modular structure using JPMS. They have identified several modules, including `DataAccess`, `BusinessLogic`, and `UserInterface`. The `BusinessLogic` module requires access to both `DataAccess` and `UserInterface`. However, the engineer is concerned about potential issues with module dependencies. Which of the following strategies should the engineer implement to ensure that the module dependencies are correctly managed and avoid runtime errors?

Accepted Answer

Use the `requires transitive` directive in the `BusinessLogic` module to automatically include dependencies from `DataAccess` to `UserInterface`.

Question 7

In a multi-threaded Java application, two threads are attempting to increment a shared counter variable simultaneously. If neither thread uses synchronization, what is the most likely outcome of this operation?

Accepted Answer

The final value of the counter may not reflect all increments due to race conditions.

Question 8

In a multi-module Gradle project, a developer notices that two modules depend on different versions of the same library, leading to a conflict during the build process. How should the developer best resolve this issue to ensure that the project builds successfully while maintaining compatibility with both modules?

Accepted Answer

Use dependency constraints to specify a single version of the library that both modules can use, ensuring compatibility.

Question 9

In a software development project, a team is tasked with creating a system to manage various types of vehicles. They decide to implement an abstract class named `Vehicle` that includes an abstract method `move()`. The team also creates two subclasses: `Car` and `Bicycle`, each implementing the `move()` method differently. During a code review, a developer suggests that the `Vehicle` class should also include a concrete method `stop()` that prints \"Vehicle stopped.\" What is the most appropriate reasoning for this design choice?

Accepted Answer

Including a concrete method in the abstract class allows all subclasses to inherit common functionality, promoting code reuse and reducing redundancy.

Question 10

In a scenario where a developer has just installed the Java Development Kit (JDK) on their system, they are attempting to run a Java application from the command line but encounter an error stating that the \'javac\' command is not recognized. After checking the installation directory, they confirm that the JDK is installed correctly. What is the most likely cause of this issue?

Accepted Answer

The JAVA_HOME environment variable is not set correctly, or the PATH variable does not include the JDK's bin directory.

Question 11

In a project where you are tasked with optimizing a Java application for faster startup times, you decide to implement Native Image Generation. However, you encounter issues with classes that utilize reflection extensively. What is the best approach to ensure that these classes are properly included in the native image?

Accepted Answer

Use the native-image tool's configuration options to specify reflection configuration files that explicitly list the classes and methods to be included.

Question 12

In a multi-threaded application, you are tasked with implementing a shared data structure that allows multiple threads to read and write data concurrently without significant performance degradation. You decide to use a concurrent collection. Given the following scenarios, which collection would be the most appropriate choice for maintaining high throughput while ensuring thread safety during frequent updates and reads?

Accepted Answer

ConcurrentHashMap

Question 13

In a multi-threaded application, you have implemented a CyclicBarrier to synchronize the completion of tasks among several worker threads. Each worker thread processes a portion of data and must wait for all other threads to finish before proceeding to the next phase of data aggregation. If one of the threads encounters an exception during its processing, what will happen when it tries to reach the barrier?

Accepted Answer

The barrier will throw a BrokenBarrierException, and all threads will be unable to proceed until the barrier is reset.

Question 14

In a software development project, a developer is tasked with creating a class hierarchy for a banking application. The base class, `Account`, contains sensitive information such as account balance and account number. The developer decides to make the account balance variable private and provides public getter and setter methods for it. However, the developer also creates a subclass called `SavingsAccount` that needs to access a method to calculate interest based on the account balance. Which access modifier should the developer use for the method that calculates interest to ensure it is accessible only within the `Account` class and its subclasses, while still maintaining encapsulation?

Accepted Answer

protected

Question 15

In a Java application, you have the following code snippet that checks the status of a user account and prints messages based on the conditions: ```java String status = \"active\"; if (status.equals(\"active\")) { System.out.println(\"Account is active.\"); if (status.equals(\"suspended\")) { System.out.println(\"Account is suspended.\"); } else { System.out.println(\"Account is not suspended.\"); } } else { System.out.println(\"Account is inactive.\"); } ``` What will be the output of this code when executed?

Accepted Answer

Account is active. Account is not suspended.

Question 16

A developer is tasked with securing a Java web application that handles sensitive user data. They decide to implement a Security Manager to restrict access to certain system resources. However, they mistakenly configure the Security Manager to grant excessive permissions to untrusted code. What is the most likely outcome of this misconfiguration?

Accepted Answer

Untrusted code may access sensitive user data and system resources, leading to potential security breaches.

Question 17

A developer is tasked with implementing a file upload feature in a Java web application. To ensure that the application adheres to security best practices, the developer decides to utilize the Java Security Manager. Which approach should the developer take to effectively restrict file access and prevent unauthorized actions?

Accepted Answer

Configure the Security Manager to allow file access only to a designated upload directory specified in the policy file.

Question 18

A development team is working on a high-performance web application that requires extensive logging for monitoring and debugging purposes. They are considering using either Log4j or SLF4J for their logging needs. The team is particularly concerned about the performance impact of logging on their application. Which logging framework would be the most suitable choice for their requirements, considering the need for flexibility and performance optimization?

Accepted Answer

SLF4J, as it provides an abstraction layer allowing for easy switching between logging frameworks without code changes.

Question 19

In a collaborative software development project, you are tasked with documenting a complex library that includes multiple classes and methods. Which approach would best ensure that your documentation is both comprehensive and user-friendly for future developers who will interact with your code?

Accepted Answer

Utilize JavaDoc comments extensively throughout your code, including detailed descriptions, examples, and relevant tags for parameters and return values.

Question 20

In a multi-threaded Java application, two threads $ T_1 $ and $ T_2 $ are incrementing a shared counter $ C $ initialized to $ C_0 $. If both threads execute their increment operations without synchronization, what will be the expected value of $ C $ after both threads have completed their execution?

Accepted Answer

$C_0 + 2$

Question 21

A software engineer is tasked with developing a feature for a real-time chat application where users can send and receive messages. The application needs to maintain the order of messages and allow for frequent additions and removals of messages as users interact. Given these requirements, which implementation of the List interface would be the most appropriate choice for storing the messages?

Accepted Answer

LinkedList

Question 22

In a software application that processes user input from a list of integers, you need to implement a loop that skips any negative numbers but stops processing entirely if a zero is encountered. Which combination of `break` and `continue` statements would best achieve this goal?

Accepted Answer

Use `continue` when a negative number is found and `break` when a zero is encountered.

Question 23

In a recent project, a developer decided to utilize the new `var` keyword introduced in Java SE 11 for declaring local variables. While refactoring a method that processes a list of user inputs, the developer wrote the following code snippet: ```java var userInput = getUserInput(); var processedInput = processInput(userInput); ``` What potential issue should the developer be aware of when using `var` in this context?

Accepted Answer

The inferred type of `userInput` may not be clear to other developers, leading to potential misunderstandings about the variable's purpose.

Question 24

In a multi-threaded application, you are tasked with implementing a shared data structure that allows multiple threads to read and update data concurrently without significant performance degradation. Given the requirements, which concurrent collection would be the most appropriate choice to ensure thread safety while maximizing throughput?

Accepted Answer

ConcurrentHashMap

Question 25

In a multi-threaded application, a main thread is responsible for processing results after several worker threads have completed their tasks. The main thread uses a CountDownLatch initialized with the number of worker threads. If one of the worker threads encounters an exception during its execution, which of the following outcomes is most likely to occur regarding the CountDownLatch and the main thread\'s execution?

Accepted Answer

The main thread will remain blocked until all worker threads call countDown(), regardless of exceptions.

Question 26

In a banking application, a developer has created a custom exception named InsufficientFundsException to handle scenarios where a withdrawal exceeds the account balance. During a code review, a colleague suggests that the exception should also include the account ID and the attempted withdrawal amount for better context. How should the developer implement this suggestion while adhering to best practices for custom exceptions?

Accepted Answer

The developer should modify the InsufficientFundsException class to include fields for account ID and withdrawal amount, and provide a constructor that initializes these fields along with a descriptive error message.

Question 27

In a software application that requires frequent lookups and updates of user preferences without the need for any specific order, which map implementation would be the most efficient choice for storing these preferences, considering both performance and memory usage?

Accepted Answer

HashMap

Question 28

In a recent project, a developer is tasked with processing a list of user inputs that may contain null values. To ensure that the application remains robust and avoids `NullPointerExceptions`, the developer decides to utilize the new API enhancements introduced in Java SE 11. Which approach should the developer take to best handle the potential absence of values in the list?

Accepted Answer

Use `Optional` to wrap the user inputs, allowing for safe handling of null values and providing methods to check for presence or absence of values.

Question 29

A developer is tasked with reading the contents of a large text file in a Java application. They want to ensure that the file is read efficiently while also handling potential I/O exceptions properly. Which approach should the developer take to achieve this goal?

Accepted Answer

Use a BufferedReader wrapped around a FileReader, and implement a try-with-resources statement to ensure the stream is closed properly.

Question 30

A developer is designing a financial application that requires precise calculations involving currency values. They need to choose a data type for storing these values. Given the potential for large numbers and the need for accuracy in decimal places, which data type would be the most appropriate for this scenario?

Accepted Answer

BigDecimal

Java SE 11 Developer Free Practice Test — 30 Questions

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