Annotations were a feature introduces in Java 5. By the way the current version of java is 8.
Annotations tell the compiler about additional information.
Annotations commonly used are :
Instance Variable
Custom Annotations
Which can be used as:
Annotations can have attributes too.
Now suppose you want to know the name of authors for all the classes created in the project. This can be done using reflection.
Now, how to use these annotations?
We can use reflection to get the list of annotations on a class
Annotations tell the compiler about additional information.
Annotations commonly used are :
@Entity @RequestMappingClass
@Resource public class Employee { }Method
@Override public void getThisDone(){ }Parameter
public void getThisDone(@RequestParam("username") String userName){ }
Instance Variable
@Id private Integer Id;
Custom Annotations
We can create our own annotations as well
public @interface Author { }
Which can be used as:
@Author public class Employee { }
Annotations can have attributes too.
public @interface Author { String name(); String date(); }
@Author(name="Hunaid",date="12-12-2016") public class Employee { }
Now suppose you want to know the name of authors for all the classes created in the project. This can be done using reflection.
Now, how to use these annotations?
We can use reflection to get the list of annotations on a class
package annot; import java.lang.annotation.Annotation; public class TestAnnotations { public static void main(String[] args) { Class aClass = Employee.class; System.out.println(aClass); Annotation[] annotations = aClass.getDeclaredAnnotations(); for(Annotation annotation : annotations){ if(annotation instanceof Author){ Author myAnnotation = (Author) annotation; System.out.println("name: " + myAnnotation.name()); System.out.println("value: " + myAnnotation.date()); } } } }
class annot.Employee name: Hunaid value: 12-12-2016
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