Java註解在不少地方被用到,在此對其進行分析並記錄,以期能更深刻的理解註解。java
Target,以下:ide
package java.lang.annotation; /** * A program element type. The constants of this enumerated type * provide a simple classification of the declared elements in a * Java program. * * <p>These constants are used with the {@link Target} meta-annotation type * to specify where it is legal to use an annotation type. * * @author Joshua Bloch * @since 1.5 */ public enum ElementType { /** Class, interface (including annotation type), or enum declaration */ TYPE, /** Field declaration (includes enum constants) */ FIELD, /** Method declaration */ METHOD, /** Parameter declaration */ PARAMETER, /** Constructor declaration */ CONSTRUCTOR, /** Local variable declaration */ LOCAL_VARIABLE, /** Annotation type declaration */ ANNOTATION_TYPE, /** Package declaration */ PACKAGE }
RetentionPolicy有三個:以下this
package java.lang.annotation; /** * Annotation retention policy. The constants of this enumerated type * describe the various policies for retaining annotations. They are used * in conjunction with the {@link Retention} meta-annotation type to specify * how long annotations are to be retained. * * @author Joshua Bloch * @since 1.5 */ public enum RetentionPolicy { /** * Annotations are to be discarded by the compiler. */ SOURCE, /** * Annotations are to be recorded in the class file by the compiler * but need not be retained by the VM at run time. This is the default * behavior. */ CLASS, /** * Annotations are to be recorded in the class file by the compiler and * retained by the VM at run time, so they may be read reflectively. * * @see java.lang.reflect.AnnotatedElement */ RUNTIME }