Adding to HashMaps in different classes

Question

I am doing a school assignment where I need to add individuals to a HashMap, as well as adding "person x knows person y" to the map. We got some code form the teacher, and I modified it a bit now. But how do I add individuals to the hash map in the other class?

there are two classes

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

public class SocialGraph {

    /**
     * The SocialGraph class stores a social
     * graph and implements * a number of methods
     * to construct and query the graph.
     */

    // The map that stores the social graph
    private HashMap<String, List<String>> map = new HashMap<String, List<String>>();

    public SocialGraph(HashMap z) {   // constructor
        map = z;
    }


    SocialGraph() {  //make a default
        map = ("Nobody", <"noone", "noone else" >);

    }

    /**
     * Add individual a to this social graph.
     * * Do nothing if a already exists in this social graph.
     */


    public void addIndividual(String a) {
        if (!map.containsKey(a)) {
            map.put(a, new ArrayList<String>());
        } else {
        }
    }
}

and also the class

    public class SocialGraphTest {

        public static void main (String [] args){
            addIndividual one = new addIndividual ("Anne");
            addIndividual two = new addIndividual ("Daisy");
            addIndividual three = new addIndividual ("Bob");
            addIndividual four = new addIndividual ("Charlie");

            one.addKnowsArrow (two);
            one.addKnowsArrow (three);
            three.addKnowsArrow (two);
            three.addKnowsArrow (four);
        }
}

I know that a few things are wrong, but I am at my wits end... Any help is much appreciated! I read the related book chapters twice, but still do not understand it.

Answer 1

Let's first start with the basics.

If you want to take a look here to understand OOP: W3s

I would suggest having an empty constructor which initializes the Map

private Map<String, List<String>> map;

public SocialGraph() {
    map = new HashMap<String, List<String>>();
}

Next, you must create a method where you add the contacts of the individual.

public void addContact(String individual, String contact) {
     if(map.containsKey(individual)) {
          map.get(individual).add(contact);
     }

     // else you can throw an exception
}

And then a method to check if an individual knows a contact.

public boolean isContact(String individual, String contact) {
     if(map.containsKey(individual)) {
          for(String c : map.get(individual)) {
              if(c.equals(contact) return true;
          }
     }

     return false;
}

Then start from creating an object at the other class and use the method.

SocialGraph socialGraph = new SocialGraph();
socialGraph.addIndividual("Tim Davalan");
socialGraph.addContact("Tim Davalan", "Aris");
boolean isContact = socialGraph.isContact("Tim Davalan", "Aris");

This is a very simple solution, of course, you can improve your design and follow well-known practices and clean code principles.

Hope it helps and if you got any question just ask :)