package com.annotation;
import java.lang.annotation.*;
// 定义一个自定义注解
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE,ElementType.FIELD,ElementType.METHOD,ElementType.CONSTRUCTOR})
@Documented
@Inherited
@interface MyAnnotation {
String value() default "";
}
// 使用自定义注解
@MyAnnotation("Class Annotation")
public class DemoClass {
@MyAnnotation("Field Annotation")
private String field;
@MyAnnotation("Constructor Annotation")
public DemoClass() {
// 构造函数注解
}
@MyAnnotation("Method Annotation")
public void demoMethod() {
// 方法注解
}
public static void main(String[] args) {
DemoClass obj = new DemoClass();
Class<? extends DemoClass> clz = obj.getClass();
// 获取类上的注解
MyAnnotation classAnnotation = clz.getAnnotation(MyAnnotation.class);
System.out.println("Class Annotation: " + classAnnotation.value());
// 获取字段上的注解
try {
java.lang.reflect.Field field = clz.getDeclaredField("field");
MyAnnotation fieldAnnotation = field.getAnnotation(MyAnnotation.class);
System.out.println("Field Annotation: " + fieldAnnotation.value());
} catch (NoSuchFieldException e) {
e.printStackTrace();
}
// 获取构造函数上的注解
try {
java.lang.reflect.Constructor<?> constructor = clz.getDeclaredConstructor();
MyAnnotation constructorAnnotation = constructor.getAnnotation(MyAnnotation.class);
System.out.println("Constructor Annotation: " + constructorAnnotation.value());
} catch (NoSuchMethodException e) {
e.printStackTrace();
}
// 获取方法上的注解
try {
java.lang.reflect.Method method = clz.getDeclaredMethod("demoMethod");
MyAnnotation methodAnnotation = method.getAnnotation(MyAnnotation.class);
System.out.println("Method Annotation: " + methodAnnotation.value());
} catch (NoSuchMethodException e) {
e.printStackTrace();
}
}
}
