{getToc} $title={Table of Contents}
Program on functional interfaces
Answer: An Interface that contains exactly one abstract method is known as a functional interface. It can have any number of default, static methods but can contain only one abstract method. It can also declare the methods of the object class.
What is the functional programming
Answer: Functional programming is a paradigm that allows programming using expressions i.e. declaring functions, passing functions as arguments, and using functions as statements
Microservice architecture and design pattern
Answer: An architectural style for developing applications. Microservices allow a large application to be separated into smaller independent parts, with each part having its own realm of responsibility.
Supplier consumer function predicate
Answer: The predicate uses the parameter to make some decision and return a boolean whereas the Consumer uses the parameter to change some of its value.
Question: Bean life cycle
Answer: When a bean is instantiated, it may be required to perform some initialization to get it into a usable state. Similarly, when the bean is no longer required and is removed from the container, some cleanup may be required.
Java Web token
Answer: JSON Web Tokens are an open, industry-standard RFC 7519 method for representing claims securely between two parties.
or
JSON Web Token is a proposed Internet standard for creating data with optional signature and/or optional encryption whose payload holds JSON that asserts some number of claims. The tokens are signed either using a private secret or a public/private key.
Internal working of HashSet hashmap and concurrent hashmap
Ans: HashSet internally uses HashMap to store its elements. Whenever you create a HashSet object, one HashMap object associated with it is also created.
Java 1.8 features:
Answer:
Lambda expressions,
Method references,
Functional interfaces,
Stream API,
Default methods,
Base64 Encode Decode,
Static methods in interface,
Optional class,
Collectors class,
ForEach() method,
Nashorn JavaScript Engine,
Parallel Array Sorting,
Type and Repeating Annotations,
IO Enhancements,
Concurrency Enhancements,
JDBC Enhancements etc.
APA gateway service discovery districts logging communication of microservices:
Answer: The API Gateway offers a reverse proxy to redirect or route requests (layer 7 routings, usually HTTP requests) to the endpoints of the internal microservices. The gateway provides a single endpoint or URL for the client apps and then internally maps the requests to a group of internal microservices.
Cyclic dependency
Answer: A circular or cyclic dependency is a situation where two or more independent modules or components rely on each other to function properly.
Comparable and comparator
Answer:
A comparable interface is used to sort the objects with natural ordering.
Comparator in Java is used to sort attributes of different objects.
Differentiate @Component, @Repository, @Service, and @Controller?
Answer:
@Component: It is a basic auto component scan annotation, it indicates the annotated class is an auto-scan component.
@Controller: Annotated class indicates that it is a controller component, and mainly used at the presentation layer.
@Service: It indicates the annotated class is a Service component in the business layer.
@Repository: You need to use this annotation within the persistence layer, this acts like a database repository.
or
To represent persistence layer components: @Repository
To represent service layer components: @Service
To represent presentation layer components: @Controller
or else you can use @Component for all of them.
Spring AOP
Answer: Spring AOP enables Aspect-Oriented Programming in spring applications. In AOP, aspects enable the modularization of concerns such as transaction management, logging, or security that cut across multiple types and objects (often termed crosscutting concerns).
or
AOP (aspect-oriented programming) is a programming style that can be adopted to define certain policies that in turn are used to define and manage the cross-cutting concerns in an application.
OAuth 2.0
Ans: The OAuth 2.0 authorization framework is a protocol that allows a user to grant a third-party website or application access to the user's protected resources, without necessarily revealing their long-term credentials or even their identity.
or
OAuth 2.0, which stands for “Open Authorization”, is a standard designed to allow a website or application to access resources hosted by other web apps on behalf of a user.
Two bins have different scopes
Answer: from the spring specs, there are five types of bean scopes supported :
1. singleton(default*): Scopes a single bean definition to a single object instance per Spring IoC container.
2. prototype: Scopes a single bean definition to any number of object instances.
3. request: Scopes a single bean definition to the lifecycle of a single HTTP request; that is each and every HTTP request will have its own instance of a bean created off the back of a single bean definition. Only valid in the context of a web-aware Spring ApplicationContext.
4. session: Scopes a single bean definition to the lifecycle of an HTTP Session. Only valid in the context of a web-aware Spring ApplicationContext.
5. global session: Scopes a single bean definition to the lifecycle of a global HTTP Session. Typically only valid when used in a portlet context. Only valid in the context of a web-aware Spring ApplicationContext.
Java memory model
Answer: Java memory model is divided between Thread Stacks (One for each thread) and a heap area.
Thread Stack: It is a thread-specific memory area and contains local variables, methods call information, etc.
JVM stacks could be of fixed size or variable size.
Memory leak:
Answer: In Java, the memory leak is a situation when the garbage collector does not recognize the unused objects and they remain in the memory indefinitely that reducing the amount of memory allocated to the application. Because the unused objects are still being referenced that may lead to OutOfMemoryError.
Select n+1 problem:
Answer: The N+1 query problem happens when your code executes N additional query statements to fetch the same data that could have been retrieved when executing the primary query.
Class loaders:
Answer: Class loaders are responsible for loading Java classes dynamically to the JVM (Java Virtual Machine) during runtime.
three different class loaders
there are three different class loaders here:
1. application
2. extension
3. bootstrap.
The application class loader loads the class where the example method is contained.
Fetching strategy in Hibernate:
Answer: Hibernate uses a fetching strategy to retrieve associated objects if the application needs to navigate the association. Fetch strategies can be declared in the O/R mapping metadata, or over-ridden by a particular HQL or Criteria query.