What are Java annotations and when to use them?

While reading some Java code, I came across annotations. I'm a beginner and I don't understand their purpose. Can someone give me a detailed explanation on what are Java annotations and when or why I should use them?

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Java annotations are a type of metadata that can be added to your code. They give additional information to the JVM, compilers, or frameworks, enhancing code functionality or giving binding instructions without changing the actual behavior. You might see them used in frameworks like Spring and Hibernate, or APIs like JAX-RS and JAXB. When to use annotations? 1. **Code Simplification**: Reduces the need for boilerplate code. For example, the `@Override` annotation in Java tells the compiler that the subsequent method overrides a method from the superclass, reinforcing good coding practices. 2. **Runtime Processing**: Annotations can be processed by your application at runtime. For example, libraries like JUnit make use of this to run unit tests that are marked with the `@Test` annotation. 3. **Compile-time checks**: Annotations can be used to instruct the compiler to enforce certain conditions, acting as a form of syntactical metadata. For instance, the `@NonNull` annotation can be used to tell the compiler to emit an error if the annotated element may be null. 4. **Frameworks Integration**: Frameworks like Spring heavily use annotations like `@Component`, `@Service`, etc., for dependency injection, event handling, and more. Learn more about them and get used to their syntax because Java annotations can be highly beneficial for reducing code complexity, dependency identification, testing, and more.
Answered on July 17, 2023.
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