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)
