ZCW-PhoneBook/PhoneBook.java

import java.util.*;

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

  public PhoneBook(TreeMap<String, String> phoneBook) {
    this.phoneBook = phoneBook;
  }

  public PhoneBook(){}

  public void add(String name, String phoneNumber){
    phoneBook.put(name, phoneNumber);
  }

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

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

  public String reverseLookup(String phoneNumber) {
    for (Map.Entry<String, String> e : phoneBook.entrySet()) {
      String name = e.getKey();
      String thisNumber = e.getValue();

      if (thisNumber == phoneNumber) {
        return name;
      }
    }
    return "Name not found";
  }

  public String display() {
    StringBuilder sb = new StringBuilder();

    for (Map.Entry<String, String> e : phoneBook.entrySet()){
      String name = e.getKey();
      String thisNumber = e.getValue();

      sb.append(name).append(" ").append(thisNumber).append("\n");
    }
    return sb.toString();
  }
}