Simple implementation of a generic Bag : Collection « Collections Data Structure « Java

Simple implementation of a generic Bag


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

 * Simple implementation of a Bag
 * @author pugh
public class Bag<E> {
  final Map<E,Integer> map;
  public Bag() {
    map = new HashMap<E, Integer>();
  public Bag(Map<E, Integer> map) { = map;
  public boolean add(E e) {
    Integer v = map.get(e);
    if (v == null) 
      map.put(e, 1);
    else map.put(e, v+1);
    return true;
  public boolean add(E e, int count) {
    Integer v = map.get(e);
    if (v == null) 
      map.put(e, count);
    else map.put(e, v+count);
    return true;
  public Set<E> keySet() {
    return map.keySet();

  public Collection<Map.Entry<E, Integer>> entrySet() {
    return map.entrySet();
  public int getCount(E e) {
      Integer v = map.get(e);
      if (v == null) 
        return 0;
      else return v;



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