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 number = ""; 
    Map<String, String> yellowPages = new TreeMap<String, String>();

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

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

    public String lookUp(String name) {
        String number = yellowPages.get(name);
        return number;
    }

    public int getSize(){

        return yellowPages.size();
    }

    public String reverseLookUp(String value) {
        String key = "";
        
        for(Map.Entry entry : yellowPages.entrySet())
        if(value.equals(entry.getValue())){
        key = entry.getKey().toString();
        
        }
        
        return key;
    }
    
    public String display() {
        Set set = yellowPages.entrySet();
        Iterator it = set.iterator();
        
        StringBuilder answerBuild = new StringBuilder();
        
        while(it.hasNext()) {
        Map.Entry x = (Map.Entry)it.next();
        answerBuild.append(x.getKey() + " : " + x.getValue());
        
        }
        
        String answer = answerBuild.toString();
        return answer;
    }
}