Optional in java 8 understanding

OptionalUnderstanding.java

package com.java8.optional;

import com.java8.businessdataobjects.Student;

import java.util.*;

public class OptionalUnderstanding {

    public static void main(String[] args) {

        System.out.println("********** 3 ways to create optional instance  *****************");
        System.out.println("1. from potential null value, 2. from non-null value, 3. empty Optionnal object");

        Car car1 = null;
        Car car2 = new Car();

        // Creating optional from optional  null / nonnull reference
        Optional<Car> optCar1 = Optional.ofNullable(car1);
        Optional<Car> optCar2 = Optional.ofNullable(car2);
        System.out.println(" From potential null value - using Optional.ofNullable : " + optCar1);
        System.out.println(" From potential non-null value - usingOptional.ofNullable : " + optCar2);

        // creating optional from non-null reference . i.e. when we are sure that reference is non null
        String str = "dsgsgfd";
        //String str=null; if str is null and we use Optional.Of this ll throw null pointer.
        Optional<String> nonNullObject = Optional.of(str);
        System.out.println("2. From non-null using Optional.Of : " + nonNullObject);

        Optional<Car> optCarEmptyObj = Optional.empty();
        System.out.println("3. Creating optional empty object : " + optCarEmptyObj);

        // creating optional usnig existing method returning null and we wrap that null to Optional object.
        Map<String, String> deliveryCoutriesIsoCodesMap = new HashMap<>();
        deliveryCoutriesIsoCodesMap.put("IN", "India");
        deliveryCoutriesIsoCodesMap.put("US", "United States");
        deliveryCoutriesIsoCodesMap.put("UK", "United Kingdom");

        System.out.println("\n**************** returning custom default value in case of potential null *********");
        System.out.println("get country name for JP : " + Optional.ofNullable(deliveryCoutriesIsoCodesMap.get("JP")).orElse("NOT_FOUND"));
        System.out.println("get country name for UK : " + Optional.ofNullable(deliveryCoutriesIsoCodesMap.get("UK")).orElse("NOT_FOUND"));

        //deliveryCoutriesIsoCodesMap.get("FF"); in code below returns null
        //System.out.println("reference to null : "+ deliveryCoutriesIsoCodesMap.get("FF").length());  // this code throws null pointer.

        System.out.println("\n*************** using Optional with existing code base which returns null from method or holds  null reference  ******************");
        List<Student> studentList = Arrays.asList(new Student(10, "Ram D", 20), new Student(18, "Zeck C", 19), new Student(11, "Tom P", 23), new Student(9, "Ronny D", 19), new Student(13, "John P", 20));

        // withoug using Optional for existing reference(method / variables)
        //System.out.println("Get student name without optional produces NullPointerException : "+findStudentByRollNo(10).getName());

        // using Optional for existing reference(method / variables)
        Optional<Student> optionalStudentByRollNo = Optional.ofNullable(findStudentByRollNo(10));
        System.out.println("Get student name with optional helps to avoid NullPointerException : " + (optionalStudentByRollNo.isPresent() ? optionalStudentByRollNo.get().getName() : "INVALID_ID"));

    }

    static Student findStudentByRollNo(Integer rollNo) {
        //some business logic which calls DAO and return a Student object or returns null for this example we ll just pass null
        return null;
    }
}

Result of execution : 
********** 3 ways to create optional instance  *****************
1. from potential null value, 2. from non-null value, 3. empty Optionnal object
 From potential null value - using Optional.ofNullable : Optional.empty
 From potential non-null value - usingOptional.ofNullable : Optional[com.java8.optional.Car@6e0be858]
2. From non-null using Optional.Of : Optional[dsgsgfd]
3. Creating optional empty object : Optional.empty

**************** returning custom default value in case of potential null *********
get country name for JP : NOT_FOUND
get country name for UK : United Kingdom

*************** using Optional with existing code base which returns null from method or holds  null reference  ******************
Get student name with optional helps to avoid NullPointerException : INVALID_ID