public class InstrumentedHashSet<E> extends HashSet<E> { 
  // The number of attempted element insertions 
  private int addCount = 0; 
 
  public InstrumentedHashSet() { 
  } 
 
  public InstrumentedHashSet(int initCap, float loadFactor) { 
    super(initCap, loadFactor); 
  } 
 
  @Override public boolean add(E e) { 
    addCount++; 
    return super.add(e); 
  } 
 
  @Override public boolean addAll(Collection<? extends E> c) { 
    addCount += c.size(); 
    return super.addAll(c); 
  } 
 
  public int getAddCount() { 
    return addCount; 
  } 
 
} 

public static void main(String[] args) { 
  InstrumentedHashSet<String> s = 
    new InstrumentedHashSet<String>(); 
  s.addAll(Arrays.asList("Snap", "Crackle", "Pop"));   
  System.out.println(s.getAddCount()); // expect 3 but 6 
} 

public class TestProperty { 
  public static void main(String[] args) { 
    Properties properties = new Properties(); 
    properties.setProperty("aaa", "aaa"); 
    properties.put("aaa", new TestPropertyObj()); 
    System.out.println(properties.getProperty("aaa")); // null 
    System.out.println(properties.get("aaa")); // com.hzy.effjava.chp3.item16.TestProperty$TestPropertyObj@5f4fcc96 
  } 
  static class TestPropertyObj { 
     
  } 
} 

public class ForwardingSet<E> implements Set<E> { 
  private final Set<E> s; 
  public ForwardingSet(Set<E> s) { this.s = s; } 
 
  public void clear()        { s.clear();      } 
  public boolean contains(Object o) { return s.contains(o); } 
  public boolean isEmpty()     { return s.isEmpty();  } 
  public int size()         { return s.size();   } 
  public Iterator<E> iterator()   { return s.iterator(); } 
  public boolean add(E e)      { return s.add(e);   } 
  public boolean remove(Object o)  { return s.remove(o);  } 
  public boolean containsAll(Collection<?> c) 
                  { return s.containsAll(c); } 
  public boolean addAll(Collection<? extends E> c) 
                  { return s.addAll(c);   } 
  public boolean removeAll(Collection<?> c) 
                  { return s.removeAll(c);  } 
  public boolean retainAll(Collection<?> c) 
                  { return s.retainAll(c);  } 
  public Object[] toArray()     { return s.toArray(); } 
  public <T> T[] toArray(T[] a)   { return s.toArray(a); } 
  @Override public boolean equals(Object o) 
                    { return s.equals(o); } 
  @Override public int hashCode()  { return s.hashCode(); } 
  @Override public String toString() { return s.toString(); } 
} 

public class InstrumentedSet<E> extends ForwardingSet<E> { 
  private int addCount = 0; 
 
  public InstrumentedSet(Set<E> s) { 
    super(s); 
  } 
 
  @Override public boolean add(E e) { 
    addCount++; 
    return super.add(e); 
  } 
  @Override public boolean addAll(Collection<? extends E> c) { 
    addCount += c.size(); 
    return super.addAll(c); 
  } 
  public int getAddCount() { 
    return addCount; 
  } 
 
  public static void main(String[] args) { 
    InstrumentedSet<String> s = 
      new InstrumentedSet<String>(new HashSet<String>()); 
    s.addAll(Arrays.asList("Snap", "Crackle", "Pop"));   
    System.out.println(s.getAddCount()); 
  } 
}