ZCW-PhoneBook/PhoneBook.java

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

/**
 * Created by Mexi Liang on 06/11/18.
 */
public class PhoneBook {
    String name = "";
    String phoneNumber= "";
    Map<String,String> phoneBook = new TreeMap<>();    
    public void addEntry(String name,String phoneNumber){
        phoneBook.put(name, phoneNumber); //add a new number
    }    
    
    public void removeEntry(String name){
        phoneBook.remove(name);//delete a number
    }
    
    public int size(){
    return phoneBook.size(); //return size of the phonebook
    }
    
    public String lookUp(String name){
    return phoneBook.get(name);
    } 
}