Which class allows multiple threads to work in parallel but blocks them until all threads are finished?
- CountDownLatch
- CyclicBarrier
- Semaphore
- ThreadGroup
The CyclicBarrier class allows multiple threads to work in parallel but blocks them until all threads have reached a certain point (barrier) in the code. Once all threads have reached the barrier, they can continue executing. It is commonly used for tasks that can be divided into subtasks that need to be completed before the main task can proceed.
Is it possible to extend a class defined as final?
- No, you cannot extend a class that is declared as final.
- Yes, you can extend a final class.
- You can extend a final class only in the same package.
- You can extend a final class, but it requires special annotations.
In Java, a class declared as "final" cannot be extended. The "final" keyword indicates that the class cannot be subclassed. Attempting to extend a final class will result in a compile-time error. This feature is often used when you want to prevent further modification or extension of a class, such as in utility classes or classes that are critical to the design.
Which method is used to retrieve the protocol type of a URL in Java?
- fetchProtocol()
- getProtocol()
- getURLProtocol()
- retrieveProtocol()
In Java, to retrieve the protocol type of a URL, you should use the getProtocol() method of the URL class. It returns a String containing the protocol, such as "http," "https," "ftp," etc. The other options do not exist as valid methods for this purpose.
Can we overload the "+" operator to concatenate two strings and add two integers in a custom class?
- No, Java does not support operator overloading.
- Yes, by defining a method named + in the custom class.
- Yes, by defining methods named add and concatenate for the custom class.
- Yes, by using the + operator with different parameter types in the method definition.
No, Java does not support operator overloading. In Java, the + operator is not overloaded for user-defined classes. The + operator is only used for addition when applied to numeric data types and for string concatenation when used with strings. Therefore, you cannot define custom behavior for the + operator in user-defined classes.
In which scenarios is it recommended to use synchronized blocks instead of synchronized methods?
- When you don't want to use synchronization at all.
- When you want to apply synchronization to a specific section of code within a method, providing more fine-grained control.
- When you want to synchronize an entire method for simplicity.
- When you want to synchronize multiple methods simultaneously.
Synchronized blocks are recommended when you want to apply synchronization to a specific section of code within a method, allowing more fine-grained control over synchronization. This can help reduce contention and improve performance in scenarios where synchronization is necessary. Synchronized methods are used when you want to synchronize the entire method for simplicity.
What is the output of the following code snippet: int[][] arr = new int[3][2]; System.out.println(arr.length);?
- 2
- 3
- 6
- The code will result in a compilation error.
In the given code, arr.length returns the number of rows in the 2D array. Here, arr is declared as a 2D array with 3 rows and 2 columns, so it prints 3, which is the number of rows.
In which sorting algorithm do larger or smaller elements "bubble" to the top of the array?
- Bubble Sort
- Merge Sort
- Quick Sort
- Selection Sort
In Bubble Sort, larger or smaller elements "bubble" to the top of the array as the algorithm repeatedly passes through the list and swaps adjacent elements if they are in the wrong order. The "bubbling" process continues until the entire list is sorted. Bubble Sort is so named due to this bubbling behavior.
How does the "diamond problem" get resolved in Java while using interfaces?
- In Java, the "diamond problem" cannot be resolved, and it leads to a compilation error.
- Java resolves the "diamond problem" by allowing classes to implement multiple interfaces with conflicting method signatures.
- The "diamond problem" is resolved by introducing explicit casting to specify which method to call when there is a conflict.
- The "diamond problem" is resolved by renaming the conflicting methods in the implementing class.
In Java, the "diamond problem" occurs when a class inherits from two or more classes that have a common ancestor with a method of the same name. To resolve this, Java allows classes to implement multiple interfaces with conflicting method signatures. This forces the implementing class to provide its own implementation, and it must explicitly call the desired method using the interface name.
If a superclass method does not throw an exception, can the overridden method in the subclass throw an exception?
- No, it cannot throw any exception
- No, it cannot throw any exception
- Yes, it can throw any exception
- Yes, it can throw any exception
In Java, if a superclass method does not declare any exceptions, the overridden method in the subclass cannot throw checked exceptions that are broader in scope than those of the superclass method. This rule is in place to ensure that the subclass does not introduce unexpected exceptions.
The ________ keyword can be used to print multi-dimensional arrays in a deep-to-string manner.
- deepToString
- display
- toString
In Java, the Arrays.deepToString() method can be used to print multi-dimensional arrays in a deep-to-string manner. This method recursively converts the array into a string representation, including nested arrays, making it useful for debugging and displaying complex data structures.