Close

Java Reflection - Field.getAnnotationsByType() Examples

Java Reflection Java Java API 

PreviousNext

Class:

java.lang.reflect.Field

java.lang.Objectjava.lang.Objectjava.lang.reflect.AccessibleObjectjava.lang.reflect.AccessibleObjectjava.lang.reflect.AnnotatedElementAnnotatedElementjava.lang.reflect.Fieldjava.lang.reflect.Fieldjava.lang.reflect.MemberMemberLogicBig

Method:

public <T extends Annotation> T[] getAnnotationsByType(Class<T> annotationClass)

Returns the target annotations that are associated with this field. If there are no target annotations associated with this element, the return value is an array of length 0. The difference between this method and AnnotatedElement.getAnnotation(Class) (Field.getAnnotation(Class) is that this method works for repeatable annotation type (Java 8).

Check out Java 8 Repeatable Annotation tutorial.


Examples


package com.logicbig.example.field;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Field;
import java.util.Arrays;

public class GetAnnotationsByTypeExample {
    @MultipleOf(3)
    private int anInt;

    public static void main(String... args) throws NoSuchFieldException {
        Field field = GetAnnotationsByTypeExample.class.getDeclaredField("anInt");
        MultipleOf[] annotations = field.getAnnotationsByType(MultipleOf.class);
        System.out.println(Arrays.toString(annotations));

        //no difference in output because our annotation is not Repeatable
        MultipleOf annotation = field.getAnnotation(MultipleOf.class);
        System.out.println(annotation);
    }

    @Target({ElementType.FIELD})
    @Retention(RetentionPolicy.RUNTIME)
    private @interface MultipleOf {
        int value() default 1;
    }
}

Output

[@com.logicbig.example.field.GetAnnotationsByTypeExample$MultipleOf(value=3)]
@com.logicbig.example.field.GetAnnotationsByTypeExample$MultipleOf(value=3)




package com.logicbig.example.field;

import java.lang.annotation.*;
import java.lang.reflect.Field;
import java.util.Arrays;

public class GetAnnotationsByTypeExample2 {
    @MultipleOf(3)
    @MultipleOf(5)
    private int anInt;

    public static void main(String... args) throws NoSuchFieldException {
        Field field = GetAnnotationsByTypeExample2.class.getDeclaredField("anInt");
        MultipleOf[] annotations = field.getAnnotationsByType(MultipleOf.class);
        System.out.println(Arrays.toString(annotations));

        //does not work:
        MultipleOf annotation = field.getAnnotation(MultipleOf.class);
        System.out.println(annotation);

        //try the container annotation
        System.out.println("-- Using the container annotation --");
        CompositeFactorOf[] annotations2 = field.getAnnotationsByType(CompositeFactorOf.class);
        System.out.println(Arrays.toString(annotations2));

        CompositeFactorOf annotation2 = field.getAnnotation(CompositeFactorOf.class);
        System.out.println(annotation2);
    }

    @Target({ElementType.FIELD})
    @Retention(RetentionPolicy.RUNTIME)
    @Repeatable(CompositeFactorOf.class)
    @interface MultipleOf {
        int value();
    }

    @Target({ElementType.FIELD})
    @Retention(RetentionPolicy.RUNTIME)
    @interface CompositeFactorOf {
        MultipleOf[] value();
    }
}

Output

[@com.logicbig.example.field.GetAnnotationsByTypeExample2$MultipleOf(value=3), @com.logicbig.example.field.GetAnnotationsByTypeExample2$MultipleOf(value=5)]
null
-- Using the container annotation --
[@com.logicbig.example.field.GetAnnotationsByTypeExample2$CompositeFactorOf(value={@com.logicbig.example.field.GetAnnotationsByTypeExample2$MultipleOf(value=3), @com.logicbig.example.field.GetAnnotationsByTypeExample2$MultipleOf(value=5)})]
@com.logicbig.example.field.GetAnnotationsByTypeExample2$CompositeFactorOf(value={@com.logicbig.example.field.GetAnnotationsByTypeExample2$MultipleOf(value=3), @com.logicbig.example.field.GetAnnotationsByTypeExample2$MultipleOf(value=5)})

See Also