Phonographic Performance Interview Questions and Answers

To create a singleton ensuring reflection does not mess up the implementation, use an enum or a private constructor with a static field.

• Use an enum to create a singleton as enums are inherently singletons and cannot be instantiated multiple times.

• Alternatively, use a private constructor with a static field to create a singleton.

• To prevent reflection from creating multiple instances, throw an exception in the constructor if an instance already exists.

Swap characters from uppercase to lowercase and lowercase to uppercase in a given string.

• Iterate through each character in the string

• Check if the character is uppercase or lowercase

• Swap the case of the character using bitwise XOR operation

• Build the resulting string with the swapped characters

ConcurrentHashMap allows multiple threads to access and modify the map concurrently, while SynchronizedHashMap ensures thread-safety by allowing only one thread to access the map at a time.

• ConcurrentHashMap is more efficient in scenarios with high concurrency as it allows concurrent read and write operations.

• SynchronizedHashMap is simpler to use and provides thread-safety, but can lead to performance degradation in highly concurrent environments.

• ConcurrentHashMap achieves thr...read more

Semaphores in Java are used for controlling access to a shared resource. They can be implemented using the java.util.concurrent package.

• Use the Semaphore class from the java.util.concurrent package

• Create a Semaphore object with an initial number of permits

• Use the acquire() method to acquire a permit before accessing the shared resource

• Use the release() method to release a permit after accessing the shared resource

Bitmask in Postgresql is used to store and manipulate multiple boolean values within a single integer column.

• Bitmask is a technique to represent a set of boolean flags using binary digits.

• In Postgresql, the bitwise operators (&, |, ^, ~) can be used to perform operations on bitmasks.

• To set a specific flag in a bitmask, use the bitwise OR operator (|).

• To check if a flag is set in a bitmask, use the bitwise AND operator (&).

• To toggle a flag in a bitmask, use the bitwise XOR ope...read more