ZCW-PhoneBook/PhoneBook.java

import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.TreeMap;

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

    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) {
        String phoneNumber = phoneBook.get(name);
        return phoneNumber;
    }

    public String reverseLookup(String value){
        String key = "";

        for(Map.Entry entry : phoneBook.entrySet())
            if (value.equals(entry.getValue())) {
                key = entry.getKey().toString();
            }
        return key;
    }

    public String display() {
        Set set = phoneBook.entrySet();
        Iterator iter = set.iterator();

        StringBuilder answer = new StringBuilder();

        while(iter.hasNext()) {
            Map.Entry i = (Map.Entry)iter.next();
            answer.append(i.getKey() + " : " + i.getValue());
        }

        String result = answer.toString();
        return result;
    }

    public int getSize() {
        return phoneBook.size();
    }
}