In a scenario where you need to add a new method to an interface that is implemented by dozens of classes without breaking existing functionality, how would you achieve this in Java 8 and above?
- Add a default method to the interface, providing a default implementation for the new method. This way, existing implementations won't be affected, and classes can choose to override the default method if needed.
- Create a separate utility class with the new method and have implementing classes use this utility class to access the new functionality.
- It's not possible to add a new method to an existing interface without breaking existing functionality in Java 8 and above.
- Use a combination of a new interface that extends the existing one with the new method and update all implementing classes to implement the new interface.
In Java 8 and above, you can add a new method to an existing interface by providing a default implementation for the new method. Existing classes that implement the interface won't be affected and can choose to override the new method if needed. This ensures backward compatibility without breaking existing functionality.
The keyword _______ is used to instantiate an object inside its own class definition.
- constructor
- instantiate
- new
- this
In Java, the keyword new is used to instantiate an object inside its own class definition. When you use new, you create a new instance of the class and allocate memory for it. The other options are not used for this purpose.
Interfaces in Java can have ________ methods from Java 8 onwards.
- Both Abstract and Static Methods
- Non-Static Methods
- Only Abstract Methods
- Only Static Methods
Starting from Java 8, interfaces in Java can have both abstract and static methods. This enhancement allows interfaces to have default method implementations using the 'default' keyword and static utility methods. However, they still cannot have instance variables.
You are given the task to refactor a long series of if-else-if conditions that check for various states of an object. The code is hard to read and maintain. What would be an efficient way to refactor this using modern Java features?
- Break the code into smaller methods
- Replace with a switch expression
- Rewrite the code in a different programming language
- Use nested if-else statements
To refactor a long series of if-else-if conditions efficiently, you can replace it with a switch expression. Switch expressions in modern Java (Java 12 and later) allow you to map different object states to specific actions cleanly and maintainably. It's a more concise and readable way to handle multiple states compared to a complex if-else chain. Breaking the code into smaller methods can improve readability, but it won't eliminate the need for conditional logic.
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.
What is the key difference in approach between the Merge Sort and Quick Sort algorithms?
- Merge Sort is a comparison-based sorting algorithm that divides the array into smaller subarrays, sorts them, and then merges them back together.
- Merge Sort is an in-place sorting algorithm that rearranges elements within the original array.
- Quick Sort is a stable sorting algorithm that maintains the relative order of equal elements.
- Quick Sort uses a divide-and-conquer approach and selects a pivot element to partition the array into two subarrays.
The key difference in approach between Merge Sort and Quick Sort lies in how they divide and conquer. Merge Sort divides the array into smaller subarrays, sorts them, and then merges them back together. Quick Sort, on the other hand, selects a pivot element and partitions the array into two subarrays, which are then sorted independently. Merge Sort is not an in-place sorting algorithm, while Quick Sort typically is.