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This article mainly introduces "what is the Java annotation processor". In the daily operation, I believe that many people have doubts about what is the Java annotation processor. The editor consulted all kinds of materials and sorted out the simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts about "what is the Java annotation processor?" Next, please follow the editor to study!

In-depth understanding of Java Annotation-Annotation processor

If there is no method and work to read annotations, annotations will not be more useful than annotations. An important part of the process of using annotations is to create them using the annotation processor. Java5 extends the API of the reflection mechanism to help programmers quickly construct custom annotation processors.

Annotation processor Class Library (java.lang.reflect.AnnotatedElement):

Java uses the Annotation interface to represent the comments in front of the program element, which is the parent interface of all Annotation types. In addition, Java adds the AnnotatedElement API to the java.lang.reflect package, which represents the program elements in the program that can accept annotations. The API mainly has the following implementation classes:

Class: class definition

Constructor: constructor definition

Field: member variable definition of a class

Method: method definition of a class

Package: the package definition of the class

The java.lang.reflect package mainly contains some tool classes that implement reflection functions. In fact, all the reflection API provided by the java.lang.reflect package expands the ability to read run-time Annotation information. When an Annotation type is defined as the runtime Annotation, the annotation can be visible at run time, and the Annotation saved in the class file when the class file is loaded will be read by the virtual machine.

The AnnotatedElement interface is the parent interface of all program elements (Class, Method, and Constructor), so after the program obtains the AnnotatedElement object of a class through reflection, the program can call the following four methods of the object to access the Annotation information:

Method 1: t getAnnotation (Class annotationClass): returns a comment of the specified type that exists on the modified program element, or null if the type annotation does not exist.

The method 2:Annotation [] getAnnotations (): returns all comments that exist on the program element. Method 3:boolean is AnnotationPresent (Class clazz) {String strFruitName= "fruit name:"; String strFruitColor= "fruit color:"; String strFruitProvicer= "supplier information:"; Field [] fields = clazz.getDeclaredFields () For (Field field: fields) {if (field.isAnnotationPresent (FruitName.class)) {FruitName fruitName = (FruitName) field.getAnnotation (FruitName.class); strFruitName=strFruitName+fruitName.value (); System.out.println (strFruitName);} else if (field.isAnnotationPresent (FruitColor.class)) {FruitColor fruitColor= (FruitColor) field.getAnnotation (FruitColor.class) StrFruitColor=strFruitColor+fruitColor.fruitColor (). ToString (); System.out.println (strFruitColor);} else if (field.isAnnotationPresent (FruitProvider.class)) {FruitProvider fruitProvider= (FruitProvider) field.getAnnotation (FruitProvider.class); strFruitProvicer= "supplier number:" + fruitProvider.id () + "supplier name:" + fruitProvider.name () + "supplier address:" + fruitProvider.address () System.out.println (strFruitProvicer);} / * output result * / public class FruitRun {/ * @ param args * / public static void main (String [] args) {FruitInfoUtil.getFruitInfo (Apple.class) }} = = Fruit name: Apple Fruit Color: RED supplier No.: 1 supplier name: Shaanxi Red Fuji Group supplier address: basic knowledge map of Java annotations for Red Fuji Building, 89 Yan'an Road, Xi'an, Shaanxi Province

At this point, the study on "what is a Java annotation processor" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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