Synechron Senior Java Developer Interview Questions and Answers

Examples of Oracle queries

• Use SELECT statement to retrieve data from a table

• Use WHERE clause to filter results based on a condition

• Use JOIN to combine rows from two or more tables based on a related column

A Spring Boot REST controller is used to handle incoming HTTP requests and return appropriate responses.

• Create a new Java class annotated with @RestController

• Define request mapping annotations like @GetMapping, @PostMapping, @PutMapping, @DeleteMapping

• Inject dependencies using @Autowired annotation

• Return response using ResponseEntity or directly as method return value

Code to reverse a comma separated string in Java

• Split the input string by comma to get an array of strings

• Iterate through the array in reverse order and append each element to a new string with a comma

• Return the reversed comma separated string

JVM memory consists of Young Generation, Old Generation, and Permanent Generation.

• Young Generation: where new objects are allocated and aged before moving to Old Generation.

• Old Generation: where long-lived objects are stored.

• Permanent Generation: where metadata such as class definitions and method information are stored.

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: In...read more

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

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...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...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 concurren...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 efficien...read more

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 ...read more

JDBC is a low-level API for connecting to databases in Java, while Hibernate is a high-level ORM framework that simplifies database interactions.

• JDBC requires writing SQL queries manually, while Hibernate provides an object-oriented approach to database operations.

• Hibernate handles mapping Java objects to database tables, while JDBC requires manual mapping.

• Hibernate provides caching mechanisms for improved performance,...read more