java中的注解机制（Annotation mechanism in Java）.docVIP

java中的注解机制（Annotation mechanism in Java） Annotation mechanism in Java Annotations (Annotation) provide a formal way of adding information to our code, which is what we can do later Use these data at a certain point (by parsing annotations to use these data). The syntax of annotations is relatively simple, except for the use of @ symbols, which is basically consistent with the inherent syntax of Java, and Java has three built-in Annotations are defined in the java.lang package. @Override indicates that the current method is the way to override the parent class. @Deprecated indicates that the current element is not used. @SuppressWarnings means shutting down some bad compiler warning messages. Here is an example of defining annotations Java code Package Test_annotation; Import java.lang.annotation.Documented; Import java.lang.annotation.Inherited; Import java.lang.annotation.Retention; Import java.lang.annotation.Target; Import java.lang.annotation.ElementType; Import java.lang.annotation.RetentionPolicy; * * meta annotations @Target, @Retention, @Documented, @Inherited * * @Target indicates where the annotation is used, and the possible ElemenetType parameters include: * ElemenetType.CONSTRUCTOR constructor declaration * ElemenetType.FIELD domain declarations (including enum instances) * ElemenetType.LOCAL_VARIABLE local variable declarations * ElemenetType.METHOD method declaration * ElemenetType.PACKAGE package declaration * ElemenetType.PARAMETER parameter declaration * ElemenetType.TYPE classes, interfaces (including annotation types) or enum declarations * * @Retention indicates which level of annotation information is saved at this level. The optional RetentionPolicy parameters include: * the RetentionPolicy.SOURCE annotation will be discarded by the compiler * the RetentionPolicy.CLASS annotation is available in the class file, but will be discarded by the VM * RetentionPolicy.RUNTIME VM will also leave annotations at runtime, so you can read the annotation in