Technical analysis of the "Annotations" framework in the Java class library

Technical analysis of the "Annotations" framework in the Java class library In the Java library, the Annotations framework is a key technology that allows developers to add metad data information to the source code.The annotation can provide additional information about the program during compilation and runtime. They will not directly affect the logic of the program, but they can provide important context information for developers and tools. Java's annotation is marked by@symbols, placed in front of class, method, member variables or parameters.Note can be used for different purposes, such as providing information about the authors and versions of the class, the purpose of the specified method and the limit of parameters, the test status of the marking method, and so on. The following is an example that demonstrates how to use the built -in annotations of Java: // Use the annotation mark a class @Deprecated public class MyClass { // Use the annotation to mark a member variable @NonNull private String name; // Use a method of annotation marking a method @Override public String toString() { return "MyClass [name=" + name + "]"; } // Use the annotation mark a parameter public void printInfo(@NotBlank String info) { System.out.println(info); } } In the above example,@defrecated annotation marks an outdated class,@Nonnull annotation marks a non -air member variable,@outerride annotation label the method to rewrite,@notblank annotation marks the method parameter non -empty string. Java's annotations are processed during the compilation phase, so they can provide additional compilation inspection.Developers can use the annotation processor to analyze the source code, generate additional code or perform other operations according to the information provided by the annotation. In addition to the built -in annotations of Java, developers can also customize their own annotations.The following is an example of a custom annotation: // Declarize a custom annotation public @interface CustomAnnotation { String value() default ""; boolean enabled() default true; } // Use custom annotations @CustomAnnotation(value = "MyAnnotation", enabled = false) public class MyClass { // ... } Custom comments are defined by adding `@interface` keywords before the annotation statement.Developers can define multiple member variables in the annotation, and set the default value by specifying the `default` keywords.Then, when using the annotation, you can provide a value for each member variable. In summary, the annotation framework in the Java class library provides a powerful mechanism that allows developers to add metad data information to the source code.They can provide important context information for developers and tools to help checked and automated during compilation.Through built -in annotations and custom annotations, developers can use the powerful functions of the annotation to improve the readability and maintenance of code.