com.google.common.collect
Class ForwardingMultiset<E>

java.lang.Object
  extended by com.google.common.collect.ForwardingObject
      extended by com.google.common.collect.ForwardingCollection<E>
          extended by com.google.common.collect.ForwardingMultiset<E>
All Implemented Interfaces:
Multiset<E>, Serializable, Iterable<E>, Collection<E>

public abstract class ForwardingMultiset<E>
extends ForwardingCollection<E>
implements Multiset<E>

A multiset which forwards all its method calls to another multiset. Subclasses should override one or more methods to modify the behavior of the backing multiset as desired per the decorator pattern.

Author:
Kevin Bourrillion
See Also:
ForwardingObject, Serialized Form

Nested Class Summary
 
Nested classes/interfaces inherited from interface com.google.common.collect.Multiset
Multiset.Entry<E>
 
Constructor Summary
protected ForwardingMultiset(Multiset<E> delegate)
          Constructs a forwarding multiset that forwards to the provided delegate.
 
Method Summary
 boolean add(E element, int occurrences)
          Adds a number of occurrences of an element to this multiset.
 int count(Object element)
          Returns the number of occurrences of an element in this multiset (the count of the element).
protected  Multiset<E> delegate()
          Returns the backing delegate object.
 Set<E> elementSet()
          Returns the set of distinct elements contained in this multiset.
 Set<Multiset.Entry<E>> entrySet()
          Returns a view of the contents of this multiset, grouped into Multiset.Entry instances, each providing an element of the multiset and the count of that element.
 boolean equals(Object obj)
          Compares the specified object with this multiset for equality.
 int hashCode()
          Returns the hash code for this multiset.
 int remove(Object element, int occurrences)
          Conditionally removes a number of occurrences of an element from this multiset, provided that at least this many occurrences are present.
 int removeAllOccurrences(Object element)
          Removes all occurrences of the specified element from this multiset.
 
Methods inherited from class com.google.common.collect.ForwardingCollection
add, addAll, clear, contains, containsAll, containsAllImpl, containsImpl, isEmpty, iterator, remove, removeAll, removeAllImpl, removeImpl, retainAll, retainAllImpl, size, toArray, toArray, toArrayImpl, toArrayImpl, toStringImpl
 
Methods inherited from class com.google.common.collect.ForwardingObject
toString
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface com.google.common.collect.Multiset
add, contains, containsAll, remove, removeAll, retainAll, toString
 
Methods inherited from interface java.util.Collection
addAll, clear, isEmpty, iterator, size, toArray, toArray
 

Constructor Detail

ForwardingMultiset

protected ForwardingMultiset(Multiset<E> delegate)
Constructs a forwarding multiset that forwards to the provided delegate.

Method Detail

delegate

protected Multiset<E> delegate()
Description copied from class: ForwardingObject
Returns the backing delegate object. This method should be overridden to specify the correct return type. For example:
  @SuppressWarnings("unchecked")
  @Override protected Foo delegate() {
    return (Foo) super.delegate();
  }
This method should always return the same delegate instance that was passed to the constructor.

Overrides:
delegate in class ForwardingCollection<E>

count

public int count(Object element)
Description copied from interface: Multiset
Returns the number of occurrences of an element in this multiset (the count of the element). Note that for an Object.equals(java.lang.Object)-based multiset, this gives the same result as Collections.frequency(java.util.Collection, java.lang.Object) (which would presumably perform more poorly).

Note: the utility method Iterables.frequency(java.lang.Iterable, java.lang.Object) generalizes this operation; it correctly delegates to this method when dealing with a multiset, but it can also accept any other iterable type.

Specified by:
count in interface Multiset<E>
Parameters:
element - the element to count occurrences of
Returns:
the number of occurrences of the element in this multiset; possibly zero but never negative

add

public boolean add(E element,
                   int occurrences)
Description copied from interface: Multiset
Adds a number of occurrences of an element to this multiset. Note that if occurrences == 1, this method has the identical effect to Multiset.add(Object). This method is functionally equivalent (except in the case of overflow) to the call addAll(Collections.nCopies(element, occurrences)), which would presumably perform much more poorly.

Specified by:
add in interface Multiset<E>
Parameters:
element - the element to add occurrences of; may be null only if explicitly allowed by the implementation
occurrences - the number of occurrences of this element to add. May be zero, in which case no change will be made.
Returns:
the previous count of this element before the operation; possibly zero - TODO: make this the actual behavior!

remove

public int remove(Object element,
                  int occurrences)
Description copied from interface: Multiset
Conditionally removes a number of occurrences of an element from this multiset, provided that at least this many occurrences are present. If the count of the element is less than occurrences, no change is made. Note that if occurrences == 1, this is functionally equivalent to the call remove(element).

Specified by:
remove in interface Multiset<E>
Parameters:
element - the element to conditionally remove occurrences of
occurrences - the number of occurrences of this element to remove. May be zero, in which case no change will be made.
Returns:
true if the condition for modification was met. Unless occurrences is zero, this implies that the multiset was indeed modified.

removeAllOccurrences

public int removeAllOccurrences(Object element)
Description copied from interface: Multiset
Removes all occurrences of the specified element from this multiset. This method complements Multiset.remove(Object), which removes only one occurrence at a time. TODO: Nuke this. Use setCount(e, 0).

Specified by:
removeAllOccurrences in interface Multiset<E>
Parameters:
element - the element whose occurrences should all be removed
Returns:
the number of occurrences successfully removed, possibly zero

elementSet

public Set<E> elementSet()
Description copied from interface: Multiset
Returns the set of distinct elements contained in this multiset. The element set is backed by the same data as the multiset, so any change to either is immediately reflected in the other. The order of the elements in the element set is unspecified.

If the element set supports any removal operations, these necessarily cause all occurrences of the removed element(s) to be removed from the multiset. Implementations are not expected to support the add operations, although this is possible.

A common use for the element set is to find the number of distinct elements in the multiset: elementSet().size().

Specified by:
elementSet in interface Multiset<E>
Returns:
a view of the set of distinct elements in this multiset

entrySet

public Set<Multiset.Entry<E>> entrySet()
Description copied from interface: Multiset
Returns a view of the contents of this multiset, grouped into Multiset.Entry instances, each providing an element of the multiset and the count of that element. This set contains exactly one entry for each distinct element in the multiset (thus it always has the same size as the Multiset.elementSet()). The order of the elements in the element set is unspecified.

The entry set is backed by the same data as the multiset, so any change to either is immediately reflected in the other. However, multiset changes may or may not be reflected in any Entry instances already retrieved from the entry set (this is implementation-dependent). Furthermore, implementations are not required to support modifications to the entry set at all, and the Entry instances themselves don't even have methods for modification. See the specific implementation class for more details on how its entry set handles modifications.

Specified by:
entrySet in interface Multiset<E>
Returns:
a set of entries representing the data of this multiset

equals

public boolean equals(Object obj)
Description copied from interface: Multiset
Compares the specified object with this multiset for equality. Returns true if the given object is also a multiset and contains equal elements with equal counts, regardless of order. TODO: caveats about equivalence-relation.

Specified by:
equals in interface Multiset<E>
Specified by:
equals in interface Collection<E>
Overrides:
equals in class Object

hashCode

public int hashCode()
Description copied from interface: Multiset
Returns the hash code for this multiset. This is defined as the sum of
  (element == null ? 0 : element.hashCode()) ^ count(element)
over all distinct elements in the multiset. It follows that a multiset and its entry set always have the same hash code.

Specified by:
hashCode in interface Multiset<E>
Specified by:
hashCode in interface Collection<E>
Overrides:
hashCode in class Object