Java Annotations

4 Key excerpts on "Java Annotations"

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  eBook - ePub

  OCP Oracle Certified Professional Java SE 11 Programmer II Study Guide

  Exam 1Z0-816 and Exam 1Z0-817

  • Scott Selikoff, Jeanne Boyarsky(Authors)
  • 2020(Publication Date)
  • Sybex

    (Publisher)

  Chapter 2 Annotations

  OCP EXAM OBJECTIVES COVERED IN THIS CHAPTER:

  • Annotations
    • Describe the purpose of annotations and typical usage patterns
    • Apply annotations to classes and methods
    • Describe commonly used annotations in the JDK
    • Declare custom annotations

  There are some topics you need to know to pass the exam, some that are important in your daily development experience, and some that are important for both. Annotations definitely fall into this last category. Annotations were added to the Java language to make a developer's life a lot easier.

  Prior to annotations, adding extra information about a class or method was often cumbersome and required a lot of extra classes and configuration files. Annotations solved this by having the data and the information about the data defined in the same location.

  In this chapter, we define what an annotation is, how to create a custom annotation, and how to properly apply annotations. We will also teach you about built-in annotations that you will need to learn for the exam. We hope this chapter increases your understanding and usage of annotations in your professional development experience.

  Introducing Annotations

  Annotations are all about metadata. That might not sound very exciting at first, but they add a lot of value to the Java language. Or perhaps, better said, they allow you to add a lot of value to your code.

  Understanding Metadata

  What exactly is metadata? Metadata is data that provides information about other data. Imagine our zoo is having a sale on tickets. The attribute data includes the price, the expiration date, and the number of tickets purchased. In other words, the attribute data is the transactional information that makes up the ticket sale and its contents.

  On the other hand, the metadata

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  eBook - ePub

  Beginning Java Programming

  The Object-Oriented Approach

  • Bart Baesens, Aimee Backiel, Seppe vanden Broucke(Authors)
  • 2015(Publication Date)
  • Wrox

    (Publisher)

  Annotations provide metadata about source code that’s not part of the program itself. Unlike comments, which are ignored by the compiler, annotations can provide information for the compiler and can be processed by some tools to generate code, documentation, or other files.

  Annotations always begin with the @ symbol. The compiler knows to expect an annotation following the @ symbol. You may have already seen some examples of annotations, such as @Test , @Before , and @After , from the unit testing section in Chapter 6.

  Some annotations can replace comments, by providing a more structured format for metadata. This metadata can then be used to automatically generate documentation for your code. These annotations can be custom-designed for use by the programmer or for consistency across a department or company.

  Other annotations are predefined in java.lang to be used in specific circumstances, such as @Deprecated , @Override , and @SuppressWarnings . @Deprecated indicates that the element, such as a method or class, has been replaced by an improved alternative and should no longer be used. Whenever an element marked @Deprecated is used in a program, the compiler will give a warning so the programmer knows to use an alternative. @Override indicates that a subclass is overriding an element from its superclass. You will learn more about this later in this chapter. By using the @Override annotation when you intend to override an element, the compiler will warn you if the method does not properly override a superclass element. @SuppressWarnings instructs the compiler to suppress specific warnings that it would normally generate. You may have seen this suggested as a solution for warnings appearing in your projects in Eclipse. Java 8 introduced a new annotation @FunctionalInterface to indicate that the programmer intends to create a functional interface according to the Java Language Specification.

  Another change in Java 8 is the flexibility to use annotations anywhere a type is used, instead of only applying to declarations as previous Java versions required. This new flexibility allows better type-checking analysis, although Java 8 does not provide this type-checking framework itself. One example of a type annotation is if you were to write a piece of code to ensure that a particular variable is never null. Then you could annotate that variable @NonNull

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  eBook - ePub

  OCP Oracle Certified Professional Java SE 11 Developer Complete Study Guide

  Exam 1Z0-815 and Exam 1Z0-816

  • Jeanne Boyarsky, Scott Selikoff(Authors)
  • 2020(Publication Date)
  • Sybex

    (Publisher)

  In this chapter, we taught you everything you need to know about annotations for the exam. Ideally, we also taught you how to create and use custom annotations in your daily programming life. As we mentioned early on, annotations are one of the most convenient tools available in the Java language.

  For the exam, you need to know the structure of an annotation declaration, including how to declare required elements, optional elements, and constant variables. You also need to know how to apply an annotation properly and ensure required elements have values. You should also be familiar with the two shorthand notations we discussed in this chapter. The first allows you to drop the elementName under certain conditions. The second allows you to specify a single value for an array element without the array braces ( {} ).

  You need to know about the various built‐in annotations available in the Java language. We sorted these into two groups: annotations that apply to other annotations and common annotations. The annotation‐specific annotations provide rules for how annotations are handled by the compiler, such as specifying an inheritance or retention policy. They can also be used to disallow certain usage, such as using a method‐targeted annotation applied to a class declaration.

  The second set of annotations are common ones that you should know for the exam. Many, like @Override and @FunctionalInterface , are quite useful and provide other developers with additional information about your application.

  Exam Essentials

  • Be able to declare annotations with required elements, optional elements, and variables. An annotation is declared with the @interface type. It may include elements and public static final constant variables. If it does not include any elements, then it is a marker annotation. Optional elements are specified with a default keyword and value, while required elements are those specified without one.
  • Be able to identify where annotations can be applied. An annotation is applied using the at ( @

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  eBook - ePub

  Hands-on Application Development using Spring Boot

  Building Modern Cloud Native Applications by Learning RESTFul API, Microservices, CRUD Operations, Unit Testing, and Deployment

  • Shagun Bakliwal(Author)
  • 2021(Publication Date)
  • BPB Publications

    (Publisher)

  HAPTER 4

  Spring Boot Annotations

  Now that we have understood the different starter packs provided by Spring Boot and auto-configuration under the hood, we will learn annotations created in the Spring Boot framework which favors the developer to save time in writing the configurations in the old convention – XML Configurations . This chapter will bring out all the annotations used with a Spring Boot application so that you can have an idea of using them before developing an application.

  Structure

  In this chapter, we will discuss the following topics:

  • Java Annotations
  • Existence of Spring annotations
  • Spring and Spring Boot annotations

  Objectives

  After studying this unit, you should be able to understand the need of annotations and the usage of Spring Boot annotations.

  Java Annotations

  Java Annotations are used to provide some kind of metadata to the Java compiler and JVM. They are embedded within the source code which tells the compiler about the behavior of the field, class, interface, or method. The annotation starts with the symbol @ followed by the name of the annotation. The following are few built-in annotations introduced in Java 1.5:

  • @Override : It is used when the child class is overriding methods of its parent class to change the behavior. The use of this annotation is necessary so that it makes the code readable and avoids any type of compilation issues if the signature of the method doesn’t match with the signature of the parent class method.
  • @Deprecated : It is used to denote the class, method, or field that should no longer be referenced in the source code. If it is used, then the Java compiler generates a warning message. For the preceding entities, if you are deprecating, then it should also be documented with @deprecated

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