注解

作用

用作于注释

可以被程序读取

元注解

处理注解的注解,一共有四个

@Target(value = ElementType.TYPE)
@Retention(value = RetentionPolicy.RUNTIME)
@Documented
@Inherited
@interface MyAnnotation {
   //参数定义 类型 + 参数名 + ()  只有一个参数，并且参数名叫value时，使用者可以省略参数名传值
   String value();
}

​

自定义注解的使用

public class Client2 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
        Class studentClass = Class.forName("Student");
        ClassAnnotation classAnnotation = (ClassAnnotation) studentClass.getAnnotation(ClassAnnotation.class);
        System.out.println(classAnnotation.db_name());
<pre><code>    Field fieldage = studentClass.getDeclaredField("age");
    FieldAnnotation fieldAnnotation = (FieldAnnotation) fieldage.getAnnotation(FieldAnnotation.class);
    System.out.println(fieldAnnotation.name() + "," + fieldAnnotation.length() + "," + fieldAnnotation.size());

}

}

@ClassAnnotation(db_name = "Stu") class Student { @FieldAnnotation(name = "cjj", length = 5, size = 9) private int age; private String name; }

@Target(value = {ElementType.TYPE}) @Retention(value = RetentionPolicy.RUNTIME) @interface ClassAnnotation { String db_name(); }

@Target(value = {ElementType.FIELD}) @Retention(value = RetentionPolicy.RUNTIME) @interface FieldAnnotation { String name();

int length();

int size();

}