ZCW-PhoneBook/PhoneBook.java

 
import java.util.List;
import java.util.ArrayList;
import java.util.TreeMap;
import java.util.Set;
import java.util.Iterator;
import java.util.Map;
import java.util.Collections;

/**
 * Created by leon on 1/23/18.
 */
public class PhoneBook {
    TreeMap<String,String> phoneMap = new TreeMap<String, String>();
    String name; 
    String phoneNumber;
    public PhoneBook(String name, String phoneNumber){
    //Constructor
    this.name = name;
    this.phoneNumber = phoneNumber;
    }
    
    public void add(String name, String phoneNumber){
        phoneMap.put(name, phoneNumber);
    }
    
    public void remove(String name){
     phoneMap.remove(name); 
    }
    
    public String lookup(String name){
     return phoneMap.get(name); 
    }
    
    public String reverseLookup(String phoneNumber){
      return phoneMap.get(phoneNumber);
    }
    
    public String display(){
        String resultString = "";
        for(String e : phoneMap.keySet()){
            String v = phoneMap.get(e);
            resultString = resultString + e + " -> " + v + "\n";
    }
    return resultString;
}
}