How to use the "annotation" framework in the Java class library

How to use the "annotation" framework in the Java class library introduction: Annotion is a metadata form in the Java class library, which provides a way to add and analyze information to the source code.Through annotations, we can describe, mark and process the code when the program is running.There are many annotations in the Java class library. At the same time, we can customize and use annotations to improve the readability, maintenance and functionality of the code.This article will introduce the basic concepts and usage methods of the annotation framework in the Java library, and provide some example code. 1. The basic concept of annotation 1.1 Definition of annotations: The annotation is a metadata form, which is declared by keywords `@Internet, and can include some member variables, methods and fields.The definition of annotations can be understood as a special interface. Its member variables are constant, and the methods are abstract methods. 1.2 Note features: The annotation can be added, parsed and used in the program source code, but unlike ordinary Java code, the annotation does not have code logic during runtime, only for description, mark and processing code. 1.3 Classification of Note: In the Java class library, the annotations can be divided into three categories: built -in annotations, standard annotations, and custom annotations. Second, built -in annotations The Java class library provides some well -defined annotations, which are often used in the process of programming and running. 2.1 `@ounerride`: Mark this method to rewrite the parent class method. If the method does not correctly rewrite the parent method, it will report an error in the compilation time. 2.2 `@deprecated`: Mark this, methods, or fields has been abandoned and not recommended. The compiler will give warning when using. 2.3 `@SUPPRESSWARNINGS`: Inhibit annotations for warnings to inhibit the compiler. 2.4 `@FunctionalInterface`: Lag the interface as a functional interface, and the compiler detects whether the interface meets the requirements of the function interface. 2.5 `@Safevarargs`: It is used to suppress warning information about unsafe parameter methods. Example code: @Override public void method () {// rewrite the parent method // ... } @Deprecated public class deprecatedClass {// abandoned class // ... } @SuppressWarnings("unchecked") public void support () {// suppress warning // ... } @FunctionalInterface Public Interface FunctionAlinterfaceExample {// function interface void method(); } @SafeVarargs Public Final <t> Void SafevararGSMethod (T ... Elements) {// variable parameter method // ... } Third, standard annotations Standard annotations are part of the Java class library, which are used to achieve specific functions and process specific problems, and no additional definition is required during use. 3.1 `@Retention`: The life cycle of specified annotations, including` Source`, `class` and` runtime`. 3.2 `@target`: Specify places where the annotation can be applied, including` Type`, `Method`,` Field` and so on. 3.3 `@documented`: The annotation indicates that the annotation can be documented and included in the generated API document. 3.4 `@inherited`: indicates that the annotation can be inherited, and the subclass will inherit the father's annotation. Example code: @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.METHOD) public @interface CustomAnnotation { // ... } @Documented public @interface DocumentedAnnotation { // ... } @Inherited public @interface InheritedAnnotation { // ... } Fourth, custom annotation In the Java library, we can also customize the annotation to specify specific marks, descriptions and processing requirements. 4.1 Definition of Note: Through the custom annotation of keywords through the keywords of the keywords, and can define some member variables and methods in it. 4.2 Use of annotations: Customized annotations can be used in the program in the form of `@4` `, or can also be referenced in other annotations. Example code: @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.METHOD) public @interface CustomAnnotation { String value () default "" ""; // member variables int count () default 0; // Member variables String [] tags () depault {}; // Array type member variable } @CustomAnnotation(value = "example") public void annotatedMethod() { // ... } @Retention(RetentionPolicy.RUNTIME) public @interface MetaAnnotation { Customannotation [] value (); // Quote other annotations } @MetaAnnotation({@CustomAnnotation("example")}) public void annotatedMethod() { // ... } Summarize: Annotion is a metadata form in the Java class library, which is used to add and analyze information to the source code.The Java class library provides built -in annotations, standard annotations, and custom annotations to achieve different functions and processing needs.Through annotations, we can improve the readability, maintenance and functionality of the code.I hope this article will help you understand the use of the annotation framework in the Java library. Note: The provided code examples are just for reference and may not be syntactically correct or complete. They are intended to demonstrate the usage of annotations in Java.