What is Java annotation? Write some facts about Java annotation

What is Java annotation?

In Java annotations are meta object in a Java source file and they do not affect the semantics of a program directly. Annotation provides a mean to describe classes, fields and methods.

Built-in Annotations in Java

• @Override
• @Deprecated
• @SuppressWarnings

Facts about Java annotations

• An annotation always starts with the @ symbol followed by the annotation name
• Annotations can provide compile-time instructions to the compiler
• All annotations extends java.lang.annotation.Annotation interface
• It is possible to create custom annotations
• Annotations are lot easier compare to XML based configuration

Usage of Java annotations

• Compilation
• IDE
• Testing framework, e.g. JUnit
• IoC container e.g. as Spring
• Serialization, e.g. XML
• Aspect-oriented programming (AOP), e.g. Spring AOP
• Documentation, e.g. XDoclet
• Application servers, e.g. EJB container, Web Service
• Object-relational mapping (ORM), e.g. Hibernate, JPA