Main.java

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        // Start your program here
        // ATTENTION: In your program, you can create only one instance of class Scanner!
        Scanner reader = new Scanner(System.in);
        Phonebook phoneBook = new Phonebook(reader);

        System.out.println("phone search");
        System.out.println("available operations: ");
        System.out.println(" 1 add a number");
        System.out.println(" 2 search for a number");
        System.out.println(" 3 search for a person by phone number");
        System.out.println(" 4 add an address");
        System.out.println(" 5 search for personal information");
        System.out.println(" 6 delete personal information");
        System.out.println(" 7 filtered listing");
        System.out.println(" x quit");

        while (true) {
            System.out.println(""); // helps formatting for testing
            System.out.print("command: ");

            String userCommand = reader.nextLine();

            if (userCommand.equalsIgnoreCase("1")) {
                phoneBook.addNumber();
            } else if (userCommand.equalsIgnoreCase("2")) {
                phoneBook.searchNumberByName();
            } else if (userCommand.equalsIgnoreCase("3")) {
                phoneBook.searchByPhoneNumber();
            } else if (userCommand.equalsIgnoreCase("4")) {
                phoneBook.addAddress();
            } else if (userCommand.equalsIgnoreCase("5")) {
                phoneBook.searchPersonalInfoByName();
            } else if (userCommand.equalsIgnoreCase("6")) {
                phoneBook.deletePersonInformation();
            } else if (userCommand.equalsIgnoreCase("7")) {
                phoneBook.searchByKeyword();
            } else if (userCommand.equalsIgnoreCase("x")) {
                break;
            }
        }
    }
}

Phonebook.java

import java.util.Set;
import java.util.HashSet;
import java.util.Map;
import java.util.HashMap;
import java.util.Scanner;
import java.util.Collection;
import java.util.Collections;
import java.util.ArrayList;
import java.util.Comparator;

public class Phonebook {

    private Map<String, Person> phoneBook = new HashMap<String, Person>();
    private Scanner reader;

    public Phonebook(Scanner reader) {
        this.reader = reader;
    }

    public void addNumber() {

        System.out.print("whose number: ");
        String name = reader.nextLine();

        if (phoneBook.containsKey(name)) { // Checks if 'phoneBook' already contains 'name'...
            Person toHaveAnotherNumberAdded = phoneBook.get(name); // if so, it retrieves the 'Person' object from 'phoneBook', and assigns it to a temporary variable.
            System.out.print("number: "); // Asks user for the new additional number...
            String number = reader.nextLine();

            toHaveAnotherNumberAdded.addPhoneNumber(number); // It then adds the number to 'Set<String> phoneNumbers' inside of 'toHaveAnotherNumberAdded'
            phoneBook.replace(name, toHaveAnotherNumberAdded);

        } else {

            System.out.print("number: "); // If phoneBook does not already contain variable 'name', asks the user for a number and then greates a new 'Person' object with 'name'
            String number = reader.nextLine();

            Person newPerson = new Person(name);
            newPerson.addPhoneNumber(number);
            phoneBook.put(name, newPerson);
        }
    }

    public void addAddress() {

        System.out.print("whose address: "); // Asks for 'name';
        String name = reader.nextLine();

        System.out.print("street: ");
        String address = reader.nextLine(); // Combines street and city into one 'address' string.
        System.out.print("city: ");
        address += " " + reader.nextLine();

        if (phoneBook.containsKey(name)) { // If 'Person' object already exists, it updates the existing address.

            Person toHaveAddressAdded = phoneBook.get(name);
            toHaveAddressAdded.setAddress(address);
            phoneBook.replace(name, toHaveAddressAdded);
            System.out.println("");

        } else {
            Person toHaveAddressAdded = new Person(name); // If 'Person' object does not already exist, it creates a new 'Person' object, and then maps it to 'phoneBook'.
            toHaveAddressAdded.setAddress(address);
            phoneBook.put(name, toHaveAddressAdded);
            System.out.println("");
        }
    }

    public void deletePersonInformation() {

        System.out.print("whose information: ");
        String name = reader.nextLine();

        if (!phoneBook.containsKey(name)) {
            System.out.println("  no information found");
        } else {
            phoneBook.remove(name);
        }

    }

    public void searchPersonalInfoByName() {
        System.out.print("whose information: ");
        String name = reader.nextLine();

        if (!phoneBook.containsKey(name)) { // returns "no information found" if empty, otherwise retrieves the information using the toString method
            System.out.println("  not found");

        } else {
            System.out.print(phoneBook.get(name).toString());
        }

    }

    public void searchNumberByName() {

        System.out.print("whose number: ");
        String name = reader.nextLine();

        if (phoneBook.containsKey(name)) {
            Set<String> numbers = phoneBook.get(name).getPhoneNumbersSet();

            for (String number : numbers) {
                System.out.println(" " + number);
            }
        } else {
            System.out.println("  not found");
        }
    }

    public void searchByPhoneNumber() {

        System.out.print("number: ");
        String number = reader.nextLine();
        int returnOrNot = 0;

        for (Person person : phoneBook.values()) {
            Set<String> phoneNumbers = person.getPhoneNumbersSet();

            if (phoneNumbers.contains(number)) {
                System.out.println(" " + person.getName());
                returnOrNot = 1;
            }
        }

        if (returnOrNot == 1) {
            return;
        } else {
            System.out.println(" not found");
        }
    }

    public void searchByKeyword() {
        System.out.print("keyword (if empty, all listed): ");
        String keyword = reader.nextLine();

        ArrayList<Person> people = new ArrayList<Person>(phoneBook.values());
        ArrayList<Person> matchedPeople = new ArrayList<Person>();

        if (keyword.isEmpty()) {
            for (Person person : people) {
                System.out.println(" " + person.getName() + "/n" + person.toString());
            }
            return;
        }

        for (Person person : people) {
            if (person.getName().contains(keyword) || person.getAddress().contains(keyword)) {
                matchedPeople.add(person);
            }
        }

        Collections.sort(matchedPeople, new Comparator<Person>() {
            public int compare(Person p1, Person p2) {
                return p1.getName().compareTo(p2.getName());
            }
        });

        if (matchedPeople.isEmpty()) {
            System.out.println(" not found");
            return;
        }

        for (Person person : matchedPeople) {
            System.out.println(" " + person.getName() + "/n" + person.toString());
        }
    }
}

Person.java

import java.util.Set;
import java.util.HashSet;

public class Person {

    private String address;
    private String name;
    private Set<String> phoneNumbers = new HashSet<String>();

    public Person(String name) {
        this.name = name;
    }

    public String getAddress() {
        if (address == null) {
            return "  address unknown";
        }
        return "  address: " + address;
    }

    public Set<String> getPhoneNumbersSet() {
        return phoneNumbers;
    }

    public String getName() {
        return name;
    }

    public String getPhoneNumbers() {
        String phoneNumbersString = "";

        if (phoneNumbers.isEmpty() || phoneNumbers == null) {
            phoneNumbers = new HashSet<String>();
            phoneNumbersString += "  phone number not found";
        } else {
            phoneNumbersString += "  phone numbers:\n";
            for (String phoneNumber : phoneNumbers) {
                phoneNumbersString += "   " + phoneNumber + "\n";
            }
        }
        return phoneNumbersString;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void addPhoneNumber(String phoneNumber) {
        phoneNumbers.add(phoneNumber);
    }

    public String toString() {

        String toString = getAddress() + "\n" + getPhoneNumbers();

        return toString;
    }
}