1.0.0 Summary
Tittle：【Java】-NO.17.EBook.4.Java.1.014-【疯狂Java讲义第3版 李刚】- Annotation
Style：EBook
Series：Java
Since：2017-11-01
End：....
Total Hours：...
Degree Of Diffculty：2
Degree Of Mastery：2
Practical Level：2
Desired Goal：2
Archieve Goal：....
Gerneral Evaluation：...
Writer:kingdelee
Related Links：
http://www.cnblogs.com/kingdelee/
1.java.lang 的 5个Annotation
api :https://docs.oracle.com/javase/9/docs/api/java/lang/package-summary.html
| Annotation Type | Description |
|---|---|
| Deprecated |
A program element annotated
@Deprecated is one that programmers are discouraged from using. |
| FunctionalInterface |
An informative annotation type used to indicate that an interface type declaration is intended to be a functional interface as defined by the Java Language Specification.
|
| Override |
Indicates that a method declaration is intended to override a method declaration in a supertype.
|
| SafeVarargs |
A programmer assertion that the body of the annotated method or constructor does not perform potentially unsafe operations on its varargs parameter.
|
| SuppressWarnings |
Indicates that the named compiler warnings should be suppressed in the annotated element (and in all program elements contained in the annotated element).
|
2.java.lang.annotation 的 6个meta Annotation
https://docs.oracle.com/javase/9/docs/api/java/lang/annotation/package-summary.html
| Annotation Type | Description |
|---|---|
| Documented |
If the annotation
@Documented is present on the declaration of an annotation type A, then any @A annotation on an element is considered part of the element's public contract. |
| Inherited |
Indicates that an annotation type is automatically inherited.
|
| Native |
Indicates that a field defining a constant value may be referenced from native code.
|
| Repeatable |
The annotation type
java.lang.annotation.Repeatable is used to indicate that the annotation type whose declaration it (meta-)annotates is repeatable. |
| Retention |
Indicates how long annotations with the annotated type are to be retained.
|
| Target |
Indicates the contexts in which an annotation type is applicable.
|
2.1 @Retention
当需要使用的注解考虑在运行时可以被程序反射读取，则在该注解上加
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation{}
2.2 @Target
用于指定注解修饰的作用域
// 我定义的注解只能修饰成员变量
@Target(ElementType.FIELD)
public @interface MyAnnotation{}
2.3 @Document
指定可以被提取出文档，一般需要出现在文档的都是必写。
2.4 @Inherited
类B继承类A，类A使用@Inherited时，类B同样继承了类A的@Inherited特性
2.5 @Repeatable
3. 反射获取注解信息