The deleteCharAt method is available in the ________ class to remove a character at a specified position.
- ArrayList
- Character
- String
- StringBuilder
The deleteCharAt method is available in the StringBuilder class in Java. It allows you to remove a character at a specified position within the StringBuilder object. The other classes mentioned do not have this method for character removal.
What value is stored at arr[1][2] after executing the following code snippet: int[][] arr = {{1,2,3}, {4,5,6}, {7,8,9}};?
- 3
- 6
- 8
- 9
The given code initializes a 2D array arr. arr[1] represents the second row (index 1), and arr[1][2] represents the third element in that row, which is 8. So, 8 is stored at arr[1][2].
The reduce() method in Java 8’s Stream API is used to ________.
- Combine elements into a single value
- Create a stream
- Perform filtering operations
- Transform elements
The reduce() method in Java 8's Stream API is used to combine elements into a single value. It can be used to perform tasks like summing up all elements, finding the maximum or minimum, or even concatenating strings in a stream. It's a fundamental operation for aggregating data.
In a scenario where order of the elements based on their insertion order is important, you might opt to use ________.
- HashMap
- HashSet
- LinkedHashMap
- TreeMap
In Java, if you want to maintain the order of elements based on their insertion order, you should opt for a LinkedHashMap. It combines the features of a hash table and a linked list to achieve this. A HashMap doesn't guarantee order, a TreeMap orders elements based on their natural order, and a HashSet doesn't guarantee any specific order.
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.