ZCW-PhoneBook/PhoneBook.java

import java.util.Map;
import java.util.TreeMap;

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

    public String add(String name, String phonenumber){
        phoneBook.put(name, phonenumber);
        return (name + " " + phoneBook.get(name));

    }

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

    public String reverseLookup(String number){
        String str = "";
        for(Map.Entry<String, String>entry : phoneBook.entrySet()){
            if(entry.getValue().equals(number)){
                str = (entry.getKey());
            }
        }
        return str;
    }

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

    public String display(){
        String result = "";
        
        for(Map.Entry<String, String> entry : phoneBook.entrySet()){
        result += (entry.getKey()) + " " + (entry.getValue() + "\n");
        }
        
        return result;
        

    }

   
}