Imagine you are developing a system where multiple transactions are handled concurrently. How would you manage to prevent dirty reads and ensure data consistency?
- Encapsulating data access logic within stored procedures or functions to prevent direct access to data.
- Implementing database isolation levels like READ_COMMITTED or SERIALIZABLE to control the visibility of data changes to different transactions.
- Using synchronized methods in Java to lock the critical section of code to prevent concurrent access to the data.
- Utilizing database transactions and employing concepts like ACID (Atomicity, Consistency, Isolation, Durability) to ensure data integrity.
In a multi-transactional system, it's crucial to manage data consistency and prevent dirty reads. Database isolation levels help in achieving this. READ_COMMITTED ensures that a transaction can't read uncommitted changes from other transactions. SERIALIZABLE provides the highest level of isolation, preventing concurrent access to the same data. It's essential to understand these concepts for maintaining data integrity.
When creating a custom exception, extending which class will make it a checked exception?
- Error
- Exception
- RuntimeException
- Throwable
When you extend the Exception class (or its subclasses), your custom exception becomes a checked exception in Java. Checked exceptions must be either caught or declared in the method signature where they are thrown.
What is the use of the transient keyword in the context of serialization?
- It forces immediate serialization of the field.
- It indicates that the field should be ignored during deserialization.
- It prevents the field from being accessed in any context.
- It specifies that the field should be stored permanently in the serialized object.
In the context of Java serialization, the transient keyword is used to indicate that a field should be ignored during the deserialization process. It ensures that the field's value is not restored from the serialized data. The other options are incorrect; transient doesn't prevent field access, store the field permanently, or force immediate serialization.
When a static synchronized method is executed, the thread holds a lock for that method's ________.
- class
- instance
- subclass
- superclass
In Java, when a static synchronized method is executed, it holds a lock for the entire class rather than an instance of the class. This means that other threads attempting to access any synchronized static method of the same class will be blocked until the lock is released, ensuring exclusive access to the class-level resource, which is "the method's ________."
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.
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 two threads are trying to access synchronized methods in a single class instance. Describe how the synchronized methods will manage the access of these two threads.
- Both threads can execute the synchronized methods concurrently, as synchronization allows multiple threads to access synchronized methods simultaneously.
- The first thread will execute the synchronized method, and the second thread will wait until the first thread completes its execution.
- The second thread will execute the synchronized method and then the first thread, as the order of execution is undefined.
- The second thread will execute the synchronized method if it has a higher priority than the first thread.
Synchronized methods in a single class instance are mutually exclusive. Only one thread can execute a synchronized method at a time. The first thread to enter the synchronized method will execute it, and the second thread will wait until the first one completes its execution. The order of execution is not defined, and thread priority does not affect synchronization.