What does the getConnection method of DriverManager class do?
- Closes an existing connection.
- Establishes a connection to a database.
- Executes a SQL query.
- Retrieves the JDBC driver's info.
The getConnection method of the java.sql.DriverManager class is used to establish a connection to a database. It takes parameters like the database URL, username, and password to create a connection to the specified database server. It does not close connections, retrieve driver info, or execute SQL queries.
In a multi-threaded environment, which class (StringBuffer or StringBuilder) would you primarily use and why?
- Both StringBuffer and StringBuilder can be used interchangeably
- Neither StringBuffer nor StringBuilder should be used in a multi-threaded environment
- StringBuffer
- StringBuilder
In a multi-threaded environment, StringBuilder is primarily used due to its better performance. Unlike StringBuffer, StringBuilder is not synchronized, which makes it more efficient when thread safety is not a concern. StringBuffer is synchronized and is used when thread safety is required. Using both interchangeably may lead to synchronization overhead.
Which data structure is preferred for implementing Binary Search effectively?
- Array
- Binary Tree
- Hash Table
- Linked List
Binary Search is most effectively implemented with a sorted array. This is because arrays provide direct access to elements by index, which is crucial for the binary search algorithm's efficiency. Binary trees and hash tables do not provide direct index-based access, making them less suitable for binary search. Linked lists can be used, but they may not offer the same performance advantages as arrays.
Synchronized methods prevent thread interference and memory consistency errors by allowing ________ thread(s) to execute the method's entire body.
- all but one
- multiple
- no additional thread(s)
- only one
Synchronized methods in Java allow only one thread to execute the method's entire body at a time. This ensures that there is no concurrent execution, preventing thread interference and memory consistency errors. Other threads are blocked until the executing thread completes the synchronized method. This is a fundamental concept in Java for ensuring thread safety.
What issues might arise if methods modifying static variables are not synchronized?
- Deadlocks may occur.
- Inconsistent or incorrect values can be assigned to static variables.
- No issues will arise.
- Only one thread can access static variables.
If methods modifying static variables are not synchronized, it can result in inconsistent or incorrect values being assigned to those variables. Since multiple threads can access and modify static variables concurrently, without synchronization, they may read and write to the variable at the same time, leading to data corruption or inconsistent state. Proper synchronization is essential to ensure thread safety when working with shared static variables.
Consider a multi-threaded environment, how can a loop potentially cause a race condition?
- The loop uses a single shared variable among multiple threads without proper synchronization, causing unpredictable results.
- The loop has a long execution time, increasing the likelihood of context switches and thread interference.
- The loop uses thread-local variables, eliminating the possibility of race conditions.
- The loop uses a synchronized keyword, ensuring thread safety.
In a multi-threaded environment, a race condition can occur when multiple threads access and modify a shared variable concurrently without proper synchronization. Option 1 correctly identifies this scenario. Option 2 refers to context switching but not directly to race conditions. Option 3 is a preventative measure, and Option 4 is a solution to race conditions, not a cause.
Which method is used to submit a task for execution to the ExecutorService and returns a Future object?
- addTaskToExecutor(Runnable task)
- execute(Runnable task)
- startTask(Callable
task) - submit(Runnable task)
The submit(Runnable task) method of the ExecutorService interface is used to submit a task for execution and returns a Future object. This Future can be used to monitor the progress and retrieve the result of the task asynchronously. The other options are not correct methods for submitting tasks to an ExecutorService.
A class in Java can contain _______, which are used to describe the properties of objects.
- Constructors
- Interfaces
- Methods
- Variables
In Java, a class can contain variables, which are used to describe the properties or attributes of objects. Methods are used to define the behaviors of objects. Constructors initialize objects, and interfaces declare methods that must be implemented.
What is the major drawback of Linear Search compared to other searching algorithms?
- Linear Search has a high time complexity.
- Linear Search is not easily implemented.
- Linear Search is not suitable for sorted data.
- Linear Search requires extra memory.
The major drawback of Linear Search is that it is not efficient for searching in large sets of sorted data. Unlike Binary Search or Hashing, which have logarithmic time complexity, Linear Search has a linear time complexity, making it slower for large datasets. It doesn't take advantage of data being sorted. The other options do not accurately represent the primary drawback of Linear Search.
Imagine that you are building a Java application to download files from an FTP server. How would you establish a connection and ensure the secure transmission of files from the server to your application?
- Employ the java.util.zip.ZipOutputStream and java.util.zip.ZipInputStream classes to compress and decompress files during transfer. Implement secure transmission using encryption libraries.
- Establish a connection using the java.io.BufferedReader and java.io.BufferedWriter classes. Ensure secure transmission through custom encryption and decryption logic.
- Establish an FTP connection using the org.apache.commons.net.ftp.FTPClient class, and enable FTPS (FTP over SSL/TLS) for secure file transfer.
- Use the java.net.Socket class to create a socket connection and implement custom encryption for secure transmission.
To establish a secure connection for downloading files from an FTP server in Java, you can use the org.apache.commons.net.ftp.FTPClient class. To ensure secure transmission, enable FTPS (FTP over SSL/TLS) in your FTP client configuration. This approach ensures that file transfers between your application and the FTP server are encrypted and secure.