AnnotatedElement

注解相关能力

public interface AnnotatedElement {}

API

A

@Inherited
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@interface A {}

B

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@interface B {}

Parent

@A
@B
class Parent {}

Child

class Child extends Parent {}

getAnnotations()

• 作用：获取当前类上的所有运行时注解
• 返回值：Annotation[]

Class<Child> clazz = Child.class;

Annotation[] annotations = clazz.getAnnotations();
for (Annotation annotation : annotations) {
    System.out.println(annotation);
}

// 可以获取到 @A
// 因为 @A 带有 @Inherited，会被 Child 继承
// 不能获取到 @B，因为 @B 没有 @Inherited

getDeclaredAnnotations()

• 作用：获取当前类直接声明的所有注解
• 返回值：Annotation[]

Class<Child> clazz = Child.class;

Annotation[] annotations = clazz.getDeclaredAnnotations();
for (Annotation annotation : annotations) {
    System.out.println(annotation);
}

System.out.println(annotations.length); // 0

getAnnotation(Class<A> annotationClass)

• 作用：获取指定类型的注解
• 返回值：A

Class<Child> clazz = Child.class;

A annotationA = clazz.getAnnotation(A.class);
B annotationB = clazz.getAnnotation(B.class);

System.out.println(annotationA != null); // true
System.out.println(annotationB != null); // false

isAnnotationPresent(Class<? extends Annotation> annotationClass)

• 作用：判断当前类上是否存在某个注解
• 返回值：boolean

Class<Child> clazz = Child.class;

boolean hasA = clazz.isAnnotationPresent(A.class);
boolean hasB = clazz.isAnnotationPresent(B.class);

System.out.println(hasA); // true
System.out.println(hasB); // false