ZCW-PhoneBook/PhoneBook.java

import java.util.TreeMap;
import java.util.Map;
import java.util.ArrayList;
import java.util.Map.Entry;

/**
 * Created by leon on 1/23/18.
 */
public class PhoneBook {
    Map<String, ArrayList> phoneBook = new TreeMap<String, ArrayList>();

    public String add(String name, String phoneNumber){
        ArrayList<String> numbers = new ArrayList<String>();
        numbers.add(phoneNumber);
        phoneBook.put(name, numbers);
        return name + " has been added.";
    }

    public int getSize(){
        return phoneBook.size();
    }

    public boolean keyExists(String name){
        return phoneBook.containsKey(name);
    }

    public String remove(String name){
        phoneBook.remove(name);
        return name + " has been deleted.";
    }

    public String lookup(String name){
        return String.join(", ", phoneBook.get(name));
    }

    public String reverseLookup(String phoneNumber){
        for(Map.Entry<String,ArrayList> entry : phoneBook.entrySet()) {
            String key = entry.getKey();
            ArrayList value = entry.getValue();
            if (value.equals(phoneNumber)) {

            }
            return entry.getKey();
        }
        return "";

    }

    public void display(){
        for(Map.Entry<String, ArrayList> entry : phoneBook.entrySet()) {
            String key = entry.getKey();
            ArrayList value = entry.getValue();
            System.out.println(key + " => " + value);
        }

    }
}