Problem In finding a collection

Question

Hi Friend,
I am having two different ways to get a data value. The data value is mapped with respect to a number or a name. By that I mean a data value can be found out on the basis of name or number. Can anyone suggest a collection or method to implement this. A code snippet will be very helpful.
Thanks,
Regards,
Ravi.

Answer 1

If you have name and number both indicating the value, then you need to be able to ensure that both are unique to the data, and to navigate name-> number and number-> name to remove values.
You need to create you own aggregate collection, something like:import java.util.*;
public class NameAndNumberMap {
  private static class NameNumberDatum {
    final String name_;
    final int number_;
    Object datum_;
    NameNumberDatum (String name, int number, Object datum) {
      name_ = name;
      number_ = number;
      datum_ = datum;
    public String toString () {
      return "<" + name_ + ", " + number_ + ", " + datum_ + ">";
  private final Map nameToDatum_ = new HashMap();
  private final Map numberToDatum_ = new TreeMap();
  public void add (String name, int number, Object datum) {
    if (nameToDatum_.containsKey(name)) {
      throw new RuntimeException("The name is not unique");
    Integer boxedNumber = new Integer(number);
    if (numberToDatum_.containsKey(boxedNumber)) {
      throw new RuntimeException("The number is not unique");
    NameNumberDatum nameNumberDatum = new NameNumberDatum(name, number, datum);
    nameToDatum_.put(name, nameNumberDatum);
    numberToDatum_.put(boxedNumber, nameNumberDatum);
  public Object get (String name) {
    NameNumberDatum nameNumberDatum = (NameNumberDatum)nameToDatum_.get(name);
    return (nameNumberDatum == null) ? null : nameNumberDatum.datum_;
  public Object get (int number) {
    NameNumberDatum nameNumberDatum = (NameNumberDatum)numberToDatum_.get(new Integer(number));
    return (nameNumberDatum == null) ? null : nameNumberDatum.datum_;
  public int number (String name) {
    NameNumberDatum nameNumberDatum = (NameNumberDatum)nameToDatum_.get(name);
    return (nameNumberDatum == null) ? Integer.MAX_VALUE : nameNumberDatum.number_;
  public String name (int number) {
    NameNumberDatum nameNumberDatum = (NameNumberDatum)numberToDatum_.get(new Integer(number));
    return (nameNumberDatum == null) ? null : nameNumberDatum.name_;
  public Object remove (String name) {
    return remove((NameNumberDatum)nameToDatum_.get(name));
  public Object remove (int number) {
    return remove((NameNumberDatum)numberToDatum_.get(new Integer(number)));
  private Object remove (NameNumberDatum nameNumberDatum) {
    if (nameNumberDatum != null) {
      nameToDatum_.remove(nameNumberDatum.name_);
      numberToDatum_.remove(new Integer(nameNumberDatum.number_));
      return nameNumberDatum.datum_;
    } else {
      return null;
  public Collection allData () {
    ArrayList allData = new ArrayList(numberToDatum_.size());
    for (Iterator valueIt = numberToDatum_.values().iterator(); valueIt.hasNext(); ) {
      allData.add(((NameNumberDatum)valueIt.next()).datum_);
    return Collections.unmodifiableList(allData);
  public Collection allNames () {
    return Collections.unmodifiableList(new ArrayList(nameToDatum_.keySet()));
  public Collection allNumbers () {
    return Collections.unmodifiableList(new ArrayList(numberToDatum_.keySet()));
  public String toString () {
    return numberToDatum_.values().toString();
  public static void main (String[] args) {
    NameAndNumberMap map = new NameAndNumberMap();
    for (int number = 0; number < 12; number ++) {
      map.add("fred " + number, number, "ginger " + (number * number));
    System.out.println(map.get(3));
    System.out.println(map.get("fred 7"));
    System.out.println(map.name(11));
    System.out.println(map.number("fred 10"));
    System.out.println(map.remove(2));
    System.out.println(map.remove("fred 4"));
    System.out.println(map.remove(12));
    System.out.println(map.remove("lemons"));
    System.out.println();
    System.out.println(map.allNames());
    System.out.println();
    System.out.println(map.allNumbers());
    System.out.println();
    System.out.println(map.allData());
    System.out.println();
    System.out.println(map);
}Pete