Constructor getAnnotation() method in Java with Examples

The getAnnotation() method of a Constructor class is used to get this constructor object annotation for the specified type if such an annotation is present, else null. Specified type is passed as parameter.

Syntax:

public <T extends Annotation> T
  getAnnotation(Class<T> annotationClass)

Parameters: This method accepts a single parameter annotationClass which represents the Class object corresponding to the annotation type.



Return value: This method returns this element’s annotation for the specified annotation type if present on this element, else null.

Exception: This method throws NullPointerException if the given annotation class is null.

Below programs illustrate the getAnnotation() method:
Program 1:

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java program to demonstrate
// Constructor.getAnnotation() method
  
import java.lang.annotation.Annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.AnnotatedType;
import java.lang.reflect.Constructor;
  
public class GFG {
  
    public static void main(String... args)
        throws NoSuchMethodException
    {
  
        // Create Constructor Object
        Constructor[] constructors
            = Demo.class.getConstructors();
  
        // Create annotation object
        Annotation annotation
            = constructors[0]
                  .getAnnotation(PathVar.class);
  
        if (annotation instanceof PathVar) {
  
            PathVar customAnnotation
                = (PathVar)annotation;
            System.out.println(
                "Path: "
                + customAnnotation.Path());
        }
    }
}
  
// Demo class
class Demo {
    public Demo(@PathVar(Path = "Demo/usr")
                String str) {}
}
  
// PathVar interface
@Target({ ElementType.TYPE_USE })
@Retention(RetentionPolicy.RUNTIME)
@interface PathVar {
    public String Path();
}

chevron_right


Output:

Path: Demo/usr

Program 2:

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java program to demonstrate
// Constructor.getAnnotation() method
  
import java.lang.annotation.Annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Constructor;
  
public class GFG {
  
    public static void main(String... args)
        throws NoSuchMethodException
    {
  
        // Create Constructor Object
        Constructor[] constructors
            = Maths.class.getConstructors();
  
        // Create annotation object
        Annotation annotation
            = constructors[0]
                  .getAnnotation(Calculator.class);
  
        System.out.println(
            "Annotation:"
            + annotation.toString());
    }
}
  
// Demo class
@Calculator(add = "Adding value",
            subtract = "Subtracting Value")
class Maths {
  
    @Calculator(add = "Adding value",
                subtract = "Subtracting Value")
    public Maths() {}
}
  
// Calculator interface
@Retention(RetentionPolicy.RUNTIME)
@interface Calculator {
    public String add();
    public String subtract();
}

chevron_right


Output:

Annotation : @Calculator(add=Adding value, subtract=Subtracting Value)

References: https://docs.oracle.com/javase/10/docs/api/java/lang/reflect/Constructor.html#getAnnotation(java.lang.Class)



My Personal Notes arrow_drop_up

I am a Developer I love to code and bring my ideas alive

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.