Re: Binary Search

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On Sat, 2 Apr 2011, Mike Schilling wrote:


Yes, and i tried not to think about it, because it's smelly. How do you
obtain these objects? Do you make them purely to use as key-holders? Does
that mean you're going to have half-filled-out instances of your value
class floating about the place? Does that mean you have to provide a
constructor that allows such instances to be created, so abandoning the
invariants that you could otherwise enforce through your constructors?

Or do you need to do something like:

public interface KeyHolder {
  public String getKey();
}

public class Value implements KeyHolder {
  private final String key;
  // other fields
  public String getKey() {
  return key;
  }
  // other methods
}

public class Example implements KeyHolder { // so called for "query by example"
  private final String key;
  public Example(String key) {
  this.key = key;
  }
  public String getKey() {
  return key;
  }
}

Map<KeyHolder, Value> objects = new TreeMap<KeyHolder, Value>(new Comparator<KeyHolder, KeyHolder>(){
  public int compare(KeyHolder a, KeyHolder b) {
  return a.getKey().compareTo(b.getKey());
  }
});
Value v = ...;
String k = v.getKey();
objects.put(v, v);
Value u = objects.get(new Example(k));
assert u == v;

?

It can certainly be done, but all things considered, i lean towards
extracting the key before hitting the map. The map could perhaps be
wrapped in a simple wrapper:

public class ValueStore {
  private Map<String, Value> map = new HashMap<String, Value>();
  public void put(Value v) {
  map.put(v.getKey(), v);
  }
  public Value get(String key) {
  return map.get(key);
  }
}

So that calling code is not troubled with the details.

tom

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