JAVA EE: Java Tutorial: Annotations in java | Java annotations [repeating Annotations in Java]

Friday, 12 May 2017

Java Tutorial: Annotations in java | Java annotations [repeating Annotations in Java]

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Java Tutorial: Annotations in java | Java annotations [repeating Annotations in Java]

Car.java

import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

/*
 * Step 1: Declare a Repeatable Annotation Type
 * 
 * The annotation type must be marked with the 
 * @Repeatable meta-annotation
 */
@Repeatable(value = Cars.class)
@interface Manufacturer
    {
        String name();
    };

/*
 * Step 2: Declare the Containing Annotation Type
 * 
 * The containing annotation type must have a value element
 * with an array type. The component type of the array type
 * must be the repeatable annotation type.
 */
@Retention(RetentionPolicy.RUNTIME)
@interface Cars
    {
        Manufacturer[] value() default
        {};
    }

@Manufacturer(name = "Mercedes Benz")
@Manufacturer(name = "Toyota")
@Manufacturer(name = "BMW")
@Manufacturer(name = "Range Rover")
public interface Car
{

}

RepeatingAnnotations.java

public class RepeatingAnnotations
{

    public static void main(String[] args)
    {

        /*
         * Retrieving Annotations using Reflection API
         * method
         */
        Manufacturer[] manufacturerArray = Car.class
                .getAnnotationsByType(Manufacturer.class);

        System.out.println("Number of car manufacturers is "
                + manufacturerArray.length);

        for (Manufacturer manufacturer : manufacturerArray)
        {
            System.out.println(manufacturer + " , name = "
                    + manufacturer.name());
        }

        System.out.println("\n-------Printing out Car Manufacturers--------");

        /*
         * Retrieving Annotations using Reflection API
         * method
         */
        Cars cars = Car.class.getAnnotation(Cars.class);
        System.out.println(cars);
        manufacturerArray = cars.value();
        for (Manufacturer manufacturer : manufacturerArray)
        {
            System.out.println(manufacturer + " , name = "
                    + manufacturer.name());
        }

    }
}

Output

Number of car manufacturers is 4
@Manufacturer(name=Mercedes Benz) , name = Mercedes Benz
@Manufacturer(name=Toyota) , name = Toyota
@Manufacturer(name=BMW) , name = BMW
@Manufacturer(name=Range Rover) , name = Range Rover

-------Printing out Car Manufacturers--------
@Cars(value=[@Manufacturer(name=Mercedes Benz), 
@Manufacturer(name=Toyota), @Manufacturer(name=BMW), 
@Manufacturer(name=Range Rover)])

@Manufacturer(name=Mercedes Benz) , name = Mercedes Benz
@Manufacturer(name=Toyota) , name = Toyota
@Manufacturer(name=BMW) , name = BMW
@Manufacturer(name=Range Rover) , name = Range Rover