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.
In Java, when a subclass has the same method as declared in the parent class, it is known as method ________.
- hiding
- inheriting
- overloading
- overriding
When a subclass has the same method name, return type, and parameters as declared in the parent class, it is known as method overriding. The subclass provides a specific implementation for that method.
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.
Externalizable interface extends ______ interface and adds two methods into it.
- Cloneable
- Externalization
- ObjectInput/Output
- Serializable
The Externalizable interface in Java extends the ObjectInput and ObjectOutput interfaces and adds two methods into it: writeExternal and readExternal. These methods are used for customized serialization of objects. The other options are not related to the Externalizable interface.
In which version of Java were Lambda expressions introduced?
- Java 6
- Java 7
- Java 8
- Java 9
Lambda expressions were introduced in Java 8. They are a significant feature that simplifies the syntax for writing anonymous functions and enhances the readability and conciseness of code in Java.
The ________ class represents a Uniform Resource Identifier and is designed to handle the complete URI syntax.
- URI
- URL
- URN
- UniformResource
The correct answer is "URI." In Java, the URI class is used to represent a Uniform Resource Identifier. It's designed to handle the complete URI syntax, including components like scheme, authority, path, query, and fragment. A URI is a broader concept that includes URLs (Uniform Resource Locators) and URNs (Uniform Resource Names).
The ________ method of the ExecutorService interface is commonly used to submit a Callable task and returns a Future object.
- execute
- invokeAll
- start
- submit
In Java, the submit method of the ExecutorService interface is used to submit a Callable task and returns a Future object representing the result of the computation. This method is commonly used for asynchronous tasks that return results.