Can an abstract class in Java have methods that are not abstract?
- No, all methods in an abstract class must be abstract.
- Yes, but they must be marked as 'final'.
- Yes, but they must be marked as 'private'.
- Yes, they can be both abstract and concrete.
In Java, an abstract class can indeed have both abstract and concrete methods. Abstract methods are meant to be overridden by subclasses, while concrete methods provide default behavior. They can have any access modifier (public, private, protected, or default).
The ________ method of the Thread class is used to determine if a thread is still running.
- isActive()
- isAlive()
- isRunning()
- isThreadRunning()
The isAlive() method of the Thread class is used to check if a thread is still running. It returns true if the thread is alive, which means it has not completed execution yet.
In a data processing application, if the data processing task fails, it needs to be retried a specified number of times. How can this be implemented using Future, Callable, and ExecutorService in Java?
- Implement a custom retry mechanism within the Callable task, where you catch exceptions, increment a retry counter, and resubmit the task if the retry limit is not reached.
- Use a separate thread to monitor the task's status and resubmit it if it fails, ensuring a specified number of retries.
- Use a try-catch block within the main method to catch exceptions and manually resubmit the task until the retry limit is reached.
- Use the ExecutorService's retryTask() method to specify the number of retries and the task to execute.
To implement data processing with retries, you can customize the Callable task to catch exceptions, increment a retry counter, and resubmit the task if the retry limit is not reached. This provides fine-grained control over retries using Future, Callable, and ExecutorService.
When a thread acquires a lock for a synchronized method, what happens to the other threads that are trying to access it?
- They are paused and put into a waiting state until the lock is released by the thread that acquired it.
- They are terminated abruptly.
- They continue to execute concurrently without any impact.
- They throw an exception immediately.
In Java, when a thread acquires a lock for a synchronized method, other threads that attempt to access the same synchronized method are paused and put into a waiting state. They will wait until the thread that acquired the lock releases it, allowing one thread to execute the synchronized method at a time.
The Timeline class in JavaFX uses instances of the ______ class to define the moment (sub-time) within relative to the cycle at which the key value is to be applied.
- KeyFrame
- TimeInstance
- TimeMarker
- TimePoint
In JavaFX, the KeyFrame class is used to define moments within a timeline where specific actions or animations should occur. It is often used with the Timeline class to specify when key values should be applied during an animation. The KeyFrame allows precise control over the timing of animations in JavaFX.
When a thread acquires a lock for a synchronized method, it ________ the entry of other threads for all synchronized methods.
- blocks
- ignores
- permits
- suspends
When a thread acquires a lock for a synchronized method, it blocks the entry of other threads for all synchronized methods in the same object or class. This means that while one thread is inside a synchronized method, other threads attempting to enter any synchronized method of the same object or class will be blocked until the lock is released by the executing thread. This ensures exclusive access to synchronized methods, preventing data corruption in multi-threaded scenarios.
Which method should be used to release the resources held by a Statement object immediately?
- close()
- execute()
- finalize()
- release()
In JDBC, the close() method should be used to release the resources held by a Statement object immediately. This method should be called when you're done using a Statement to free up resources, like database connections and memory. The other options do not serve this purpose.
Which of the following classes are byte stream classes in Java?
- FileInputStream and FileOutputStream
- FileInputStream and Reader
- FileReader and FileOutputStream
- FileReader and Writer
Byte stream classes in Java are used for handling binary data. The correct options are FileInputStream and FileOutputStream, as they are used to read and write binary data to files. FileReader and Reader are character stream classes used for reading text data, not binary data.
What is the difference between an abstract class and an interface when Java 8 introduced default methods in interfaces?
- An abstract class can contain both abstract and concrete methods, whereas an interface can only have abstract methods.
- An abstract class cannot be extended, but an interface can be implemented.
- An abstract class cannot have any methods with default implementations, while an interface can have default methods.
- An abstract class cannot have constructors, but an interface can have default constructors.
In Java 8, interfaces were enhanced to support default methods, which provide a default implementation. The key difference between an abstract class and an interface is that an abstract class can have both abstract and concrete methods, whereas an interface can only have abstract methods. This allows for multiple inheritance of behavior through interfaces while maintaining the ability to inherit state through abstract classes.
Which sorting algorithm repeatedly steps through the list, compares adjacent elements, and swaps them if they are in the wrong order?
- Bubble Sort
- Insertion Sort
- Merge Sort
- Quick Sort
Bubble Sort is a simple sorting algorithm that repeatedly steps through the list to be sorted, compares adjacent elements, and swaps them if they are in the wrong order. It is known for its simplicity but is less efficient than other sorting algorithms like Quick Sort and Merge Sort in terms of time complexity.