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:
// 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 classclass Demo { public Demo(@PathVar(Path = "Demo/usr") String str) {}} // PathVar interface@Target({ ElementType.TYPE_USE })@Retention(RetentionPolicy.RUNTIME)@interface PathVar { public String Path();} |
Output:
Path: Demo/usr
Program 2:
// 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();} |
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)
