How to Illustrate Type annotations in java8

    Annotations are the information that can be treated as supplement about the program. It is used to associate with the meta data. Generally, it contains the information about classes, methods, constructors, variables and so on…

Syntax:

@Annotation_Information

Eg: @FunctionalInterface

Built in package for annotation is java.lang.annotation

Where to use annotations??

              Mainly, annotations are used in declaration. It can declare a class, member functions, variables and so on. In java8, it deals with types. So, it is called Type annotations.

Type annotations are very useful in object creation, type casting an element, implements and thrown statements.

Some of the examples are given below.

1.       Object creation:

This is used to create an object for a class.

Eg:

new @Class1 Obj(); where new is the keyword to create an object. @Class1 is the class. Obj() is the object name.

2.       Type casting:

It is the process of converting one datatype to another.

              Eg: a = (@NonNull int) b;

3.       Using thrown:

Thrown is an exception. This can be implemented by as follows.

              Eg: void SampleMethod() throws

@Critical  MethodException()

{

---------------

}

4.       Using Implements:

        “Implements” is one of the clause used in java.

Eg: class SampleList<L> implements

      @ReadOnly List<@Readonly L>

      {

      …………

      }

          These are the ways of type annotations are used.

        Now, a java program to illustrate type annotation is given below.

Java program to illustrate Type Annotation:

              This java program has following steps to implement the type annotation.

Steps:

• As a beginning of the program, include the built in packages.
• Create a type annotation @Target.
• Implement it using an interface @interface.
• Create a public class TypeAnnotationEg and save it.
• Inside the main function, create a type annotation with a string str. Displays the message as “It is a type annotation example” using system.out.println.
• Call the Msg() function.
• Inside the Msg(), print the message.

//Java program to illustrate type annotation

import java.lang.annotation.ElementType;

import java.lang.annotation.Target;

@Target(ElementType.TYPE_USE)

@interface TypeAnnoIf{}

public class TypeAnnotationEg {

              public static void main(String[] args) {

                            @TypeAnnoDemo String str = "It is a type annotation example";

                             System.out.println(str);

                             Msg();

              }

              static @TypeAnnoIf int Msg() {

              System.out.println("The return data is annotated");

              return 0;

              }

}

Compile and run the program to print the output.

C:\raji\blog>javac TypeAnnotationEg.java

C:\raji\blog>java TypeAnnotationEg

It is a type annotation example

The return data is annotated

     Sometimes annotations are alternative to XML and JMI(Java Marker Interface).Annotations