Re: Retrieve the key from a map (2)

Chris Uppal wrote:


and inability to reuse existing code, developed for unrelated
applications, that does one, but not both, of the jobs.

The following would need a remove method added, but it should be obvious
how to do that.

/*
  * Created on Aug 14, 2004
  */
package utilities;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

/**
  * Utility class for counting instances of equal objects.
  */
public class Counter {

   private Map<Object,Count> data = new HashMap<Object,Count>();

   /**
    * Increment by one the count associated with a specified
    * key.
    * @param key
    */
   public void increment(Object key) {
     Count count = data.get(key);
     if (count == null) {
       count = new Count();
       data.put(key, count);
     }
     count.increment();
   }

   /**
    * Get the count associated with a specified key.
    * @param key The key whose count is required.
    * @return The number of times increment has been called with
    * a key equal to this one.
    */
   public int get(Object key) {
     Count count = data.get(key);
     if (count == null) {
       return 0;
     } else {
       return count.get();
     }
   }

   /**
    * Get number of unique counted objects
    *
    * @return Number of key objects for which increment
    * has been called. Equal objects are only counted once.
    */
   public int size() {
     return data.size();
   }

   /**
    * Get all the unique counted objects
    * @return A set containing a refence to the counted objects.
    */
   public Set getKeys() {
     return Collections.unmodifiableSet(data.keySet());
   }

   private static class Count {
     private int val = 0;

     private void increment() {
       val++;
     }

     private int get() {
       return val;
     }
   }

}