ZCW-PhoneBook/PhoneBook.java

import java.util.*;

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

    public void addEntry(String name, String... phoneNumbers){
        phoneBook.put(name, Arrays.asList(phoneNumbers));
    }

    public void removeEntry(String name){
        phoneBook.remove(name);
    }

    public void addNumberToEntry(String name, String... phoneNumbers){
        List<String> listToUpdate = new ArrayList<>(phoneBook.get(name));
        for (String aNumber : phoneNumbers){
            listToUpdate.add(aNumber);
        }
        String[] updatedNumbers = listToUpdate.toArray(new String[listToUpdate.size()]);
        addEntry(name, updatedNumbers);
    }

    public void removeNumberFromEntry(String name, String... phoneNumbers){
        List<String> listToUpdate = new ArrayList<>(phoneBook.get(name));
        Iterator<String> i = listToUpdate.iterator();
        while(i.hasNext()){
            String aNumberInList = i.next();
            for (String aNumberToDelete : phoneNumbers){
                if (aNumberInList.equals(aNumberToDelete)){
                    i.remove();
                }
            }
        }
        String[] updatedNumbers = listToUpdate.toArray(new String[listToUpdate.size()]);
        addEntry(name, updatedNumbers);
    }

    public String lookup(String name){
        if(phoneBook.get(name)==null){
            return null;
        }
        StringBuilder numbers = new StringBuilder();
        int counter = 0;
        for (String aNumber : phoneBook.get(name)){
            numbers.append(aNumber);
            counter++;
            if(counter != phoneBook.get(name).size()){
                numbers.append(", ");
            }
        }
        return numbers.toString();
    }

    public String reverseLookup(String... phoneNumbers){
        for(Map.Entry<String, List<String>> e : phoneBook.entrySet()){
            String name = e.getKey();
            for(String aNumberInList : phoneBook.get(name)){
                for (String aNumberToLookup : phoneNumbers){
                    if(aNumberInList.equals(aNumberToLookup)){
                        return e.getKey();
                    }
                }
            }
        }
        return null;
    }

    public void display(){
        System.out.printf("%-20s%-12s\n", "Name", "Phone Number(s)");
        for(Map.Entry<String, List<String>> e : phoneBook.entrySet()){
            String printName = e.getKey();
            List<String> printNumber = e.getValue();
            System.out.printf(" %-20s %-12s\n", printName, printNumber);
        }
        System.out.printf("-----End of the phone book-----\n");
    }
}