DB4o HashMap toString()

Question

As a learning tool for DB4o and Java I have started to create a Telephone Directory. To do this I create an instance of a TelephoneDirectory which contains a year and a HashMap of entries.

public class TelephoneDirectory {
  private int year;
  private HashMap<String, String> hashmap;

  public TelephoneDirectory(int year) {
    this.year = year;
    this.hashmap = new HashMap<String, String>();
  }

  public int getYear() {
    return year;
  }

  public HashMap getHashmap() {
    return hashmap;
  }

  public void addEntry(String name, String number) {
    hashmap.put(number, name);
  }
}

So I add a few entries with addEntry. What I would like to do is search through the telephone directory for a specific name. For this I use QueryByExample (QBE), like so:

public static void lookupName(String name, int year, ObjectContainer db) {

  TelephoneDirectory proto = new TelephoneDirectory(year);
  proto.addEntry(name, null);

  ObjectSet result=db.queryByExample(proto);

  System.out.println("Size:" + result.size());
  while(result.hasNext()) {
    System.out.println(result.next());
  }
}

The issue that I am having with this is that if a result is found in the hashmap, then I need the key/value pair to be printed. So far the output is:

Size:1 telephonedirectory.TelephoneDirectory@da4b71

This is obviously because there is no toString() method. But what do I put in the toString() method as only a subset of hashmap values will be present in the result.

Example

TelephoneDirectory dir = new TelephoneDirectory(2011);
dir.addEntry("12345", "Adam");
dir.addEntry("67890", "Bob");
dir.addEntry("24680", "Carl");

And I then query:

lookupName("Bob", 2011, db);

Expected Result:

2011 - 67890: Bob

I am sure that it is something simple that I am overlooking.

Thanks in advance.

EDIT: I just realized that I am using an ObjectSet as the result of QBE. It doesn't seem to give me any more light on the problem, but maybe it provides a different implementation method?

UPDATE: Based on the efforts of PeterMmm I have now adjusted his reply to the following:

  @Override
  public String toString() {
    StringBuilder sb = new StringBuilder();

    sb.append(year + "\n");
    for (Object k : hashmap.keySet()) {
       sb.append(k + ": " + this.lookupName((String)k) + "\n");
    }

    return sb.toString();
  }

The problem here of course is that the toString method still uses the whole instance hashmap i.e. hashmap.keySet(); instead of ObjectSet result and so, on a search of "bob" all results are returned i.e. "Adam, Bob and Carl"

The FULL answer: The problem has now been resolved but only partly due to the answer given so I will mark it as the best answer but give full details below.

Not only should I include the toString I also needed to manipulate the ObjectSet, and because the query was based over a TelephoneDirectory I was able to cast the ObjectSet back to a TelephoneDirectory. In doing this I was then able to manipulate the TelephoneDirectory using it's own instance methods.

Thank you very much for your time and effort.

Answer 1

Anothe way to implement the directory would be:

public class TelephoneEntry {
  private int year;
  private String name;
  private String tel;

  ....
}

The collection that you manage thru hashmap will be managed by db4o for you.

Update After short discussion, you may override TelephoneDirectory.toString() :

class TelephoneDirectory {

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        for (Object k : hashmap.keySet()) {
            // details for you 
        }
        return sb.toString();
    }
}