Optimum Technology Interview Questions and Answers

Immutable classes in Java are classes whose objects cannot be modified once they are created.

• Make the class final to prevent inheritance

• Make all fields private and final

• Do not provide setter methods for fields

• Ensure that any mutable objects within the class are also immutable

Use @Primary to specify a primary bean when multiple beans of the same type are present. Use @Qualifier to specify a specific bean when multiple beans of the same type are present.

• Use @Primary to indicate the primary bean to be used when multiple beans of the same type are present in the Spring application context.

• Use @Qualifier along with @Autowired to specify a specific bean to be injected when multiple beans of the same type are present.

• Example: @Primary annotation can be ...read more

Composition is a strong relationship where the child object cannot exist independently of the parent object, while aggregation is a weak relationship where the child object can exist independently.

• Composition is a 'has-a' relationship, where the child object is a part of the parent object.

• Aggregation is a 'has-a' relationship, where the child object is not a part of the parent object.

• In composition, the child object is created and destroyed along with the parent object.

• In agg...read more

Interface is a contract with no implementation, while abstract class can have some implementation.

• Interface cannot have any method implementation, while abstract class can have some method implementations.

• A class can implement multiple interfaces, but can only extend one abstract class.

• Interfaces are used to achieve multiple inheritance in Java.

• Abstract classes can have constructors, while interfaces cannot.

• Example: Interface - Runnable, Abstract Class - Animal with abstract ...read more

HashMap is not thread-safe while ConcurrentHashMap is thread-safe.

• HashMap is not thread-safe and can lead to ConcurrentModificationException if modified during iteration.

• ConcurrentHashMap allows concurrent read and write operations without the need for external synchronization.

• ConcurrentHashMap achieves thread-safety by dividing the map into segments, allowing multiple threads to operate on different segments concurrently.

• ConcurrentHashMap is more suitable for multi-threaded ...read more

Comparable is an interface used for natural ordering of objects, while Comparator is an interface used for custom ordering of objects.

• Comparable interface is implemented by the class whose objects are to be compared, while Comparator interface is implemented by a separate class.

• Comparable interface has a single method compareTo() for comparing objects, while Comparator interface has a single method compare() for custom comparison logic.

• Comparable interface is used for natural...read more

Collections store data while streams process data in a functional way.

• Collections are used to store and manage groups of objects, while streams are used to process collections of objects.

• Collections are mutable, meaning you can add, remove, or modify elements, while streams are immutable and do not change the original data.

• Streams use functional programming concepts like map, filter, and reduce to process data efficiently.

• Collections are eager, meaning they store all elements...read more