Java注解机制分析

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
}

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
}