What will be the result of the expression !!true?
- Compilation Error
- FALSE
- Runtime Error
- TRUE
The expression !!true is a double negation of the boolean value true. It will result in true. The first ! operator negates true to false, and the second ! operator negates false back to true. This is a common way to ensure a boolean value is truly true.
Which method is used to retrieve the InputStream of a Socket object?
- getInputStream()
- getOutputStream()
- getSocketInputStream()
- openInputStream()
In Java, you can retrieve the InputStream of a Socket object using the getInputStream() method. This input stream allows you to read data from the socket. The other options are not used for retrieving the input stream of a socket.
Which of the following statements is/are true regarding the final keyword when used with variables?
- A final variable can only be initialized once and cannot be changed afterward.
- A final variable must be initialized at the time of declaration.
- Final variables are automatically initialized with the default value for their data type.
- Final variables can be changed in any method of the class.
When the "final" keyword is used with variables in Java, it indicates that the variable's value can only be assigned once, and after that, it cannot be changed. This enforces immutability and is often used for constants. The other options are incorrect. A final variable must be initialized either at the time of declaration or in the constructor of the class. Final variables are not automatically initialized.
Imagine you are developing a system that requires scheduling of tasks, like sending notifications, at fixed-rate intervals. How would you implement this using concurrency utilities in Java?
- Use CachedThreadPoolExecutor: Dynamically adjust thread pool size to handle scheduling tasks efficiently.
- Use FixedThreadPoolExecutor: Allocate a fixed number of threads for scheduling tasks.
- Use ScheduledThreadPoolExecutor: Schedule tasks with fixed-rate intervals using scheduleAtFixedRate method.
- Use SingleThreadPoolExecutor: Execute tasks one by one with fixed-rate intervals to ensure sequential processing.
For scheduling tasks at fixed-rate intervals, the ScheduledThreadPoolExecutor is the most appropriate choice. It provides methods like scheduleAtFixedRate to achieve this functionality. CachedThreadPoolExecutor and SingleThreadPoolExecutor do not specialize in scheduling tasks, and using FixedThreadPoolExecutor is not optimal for scheduling.
What will be the output of calling a method overridden in the child class?
- It depends on how the method is called
- It depends on the method's signature
- The child class's method will always be called
- The parent class's method will always be called
When a method is overridden in the child class, the version of the method in the child class is called when the method is invoked on an instance of the child class. This is known as method overriding and is a fundamental concept in object-oriented programming.
In a multithreaded application where multiple threads are reading and writing to a shared User object, how would you ensure that the read and write operations are thread-safe?
- Ensure that all threads run in a single thread by using a single-core CPU.
- Implement a ReadWriteLock to control access to the User object.
- Use synchronized methods for read and write operations on the User object.
- Use the volatile keyword for the User object.
To ensure thread safety in a multithreaded application, you can use synchronized methods for read and write operations on the shared User object. This prevents multiple threads from accessing and modifying the object simultaneously, avoiding data corruption and race conditions. The other options do not provide effective thread safety mechanisms.
The ______ method of the Lock interface is used to acquire the lock.
- acquire()
- lock()
- tryLock()
- unlock()
The lock() method of the Lock interface is used to acquire the lock. It blocks until the lock is available and then acquires it. The unlock() method is used to release the lock. The acquire() and tryLock() methods are not part of the standard Lock interface in Java.
Consider a scenario where you have a large number of short-lived asynchronous tasks. Which type of ExecutorService would you consider using and why?
- CachedThreadPoolExecutor: A thread pool that dynamically creates and recycles threads.
- FixedThreadPoolExecutor: A fixed-size thread pool with a specific number of threads.
- ScheduledThreadPoolExecutor: A thread pool for scheduling tasks at a fixed rate or delay.
- SingleThreadPoolExecutor: A single-threaded ExecutorService.
In this scenario, the CachedThreadPoolExecutor is suitable. It dynamically adjusts the number of threads based on the workload, making it efficient for short-lived tasks. SingleThreadPoolExecutor and FixedThreadPoolExecutor have limitations for such cases, and ScheduledThreadPoolExecutor is designed for scheduling tasks, not managing short-lived tasks.
The ________ interface is used to execute SQL stored procedures.
- CallableStatement
- Connection
- PreparedStatement
- Statement
In JDBC, the CallableStatement interface is used to execute SQL stored procedures. It allows you to call stored procedures that may take parameters and return values. Statement is used for executing regular SQL statements, Connection is used for establishing database connections, and PreparedStatement is used for executing parameterized SQL queries.
The ________ data type in Java can store decimal numbers up to 15 decimal places.
- BigDecimal
- double
- float
- long
In Java, the BigDecimal data type is used to store decimal numbers with precision up to 15 decimal places. It is commonly used in financial and scientific applications where high precision is required. The float and double types have limited precision and are not suitable for this purpose.