Question

Java: modify the given example code to make it possible to create a student object by only specifying the name, all other info may be absent. it may also be possible to add a tag with an absent value. use OPTIONAL TYPE and NULL object design pattern.  

import java.util.HashMap;
import java.util.Map;

public class Student
{
   private final String aName;
   private String aGender;
   private int aAge;
   private Country aCountry;
   private Map aTags = new HashMap<>();
   
   public Student(String pName)
   {
      aName = pName;
   }
   
   public String getName()
   {
      return aName;
   }
   //getGender, getAge, getCountry, getTag

   public void editTag(String pTag, String pValue)
   {
      aTags.put(pTag, pValue);
   }
}

Answer 1

creating student with name JACK and no gender and age. except name, all fields are optional

Code with comments

Temp.js (driver class)

import java.util.HashMap;

import java.util.Map;

import java.util.Optional;

class Temp {

    public static void main(String[] args) {

        Student stud = new Student("JACK");

        System.out.println(stud.getName());

        System.out.println(stud.getGender());

        System.out.println(stud.getAge());

    }

}

class Country {

}// define your class

class Student {

    private final String aName;

    private Optional<String> aGender; // optional fields

    private Optional<Integer> aAge; // optional fields

    private Optional<Country> aCountry; // optional fields

    private Optional<Map> aTags; // optional fields

    public Student(String pName) {

        aName = pName;

        aGender = Optional.ofNullable(null); // setting null

        aAge = Optional.ofNullable(null); // setting null

        aCountry = Optional.ofNullable(null); // setting null

        aTags = Optional.of(new HashMap<>()); // initializing with empty map

    }

    public String getName() {

        return aName; // return name

    }

    // getGender, getAge, getCountry, getTag

    public void editTag(String pTag, String pValue) {

        aTags.get().put(pTag, pValue);

    }

    public String getGender() {

        return aGender.orElse("Unknown Gender"); // return if present otherwise this parameter

    }

    public Integer getAge() {

        return aAge.orElse(-1);// return if present otherwise this parameter

    }

    public Country getCountry() {

        return aCountry.orElse(null);// return if present otherwise this parameter

    }

    public Map getTags() {

        return aTags.get();

    }

}