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>, 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

Nested Class Summary
 
Nested classes/interfaces inherited from interface com.google.common.collect.Multiset
Multiset.Entry<E>
 
Constructor Summary
ForwardingMultiset()
           
 
Method Summary
 int 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 abstract  Multiset<E> delegate()
          Returns the backing delegate instance that methods are forwarded to.
 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 object)
          Indicates whether some other object is "equal to" this one.
 int hashCode()
          Returns a hash code value for the object.
 int remove(Object element, int occurrences)
          Removes a number of occurrences of the specified element from this multiset.
 int setCount(E element, int count)
          Adds or removes the necessary occurrences of an element such that the element attains the desired count.
 boolean setCount(E element, int oldCount, int newCount)
          Conditionally sets the count of an element to a new value, as described in Multiset.setCount(Object, int), provided that the element has the expected current count.
 
Methods inherited from class com.google.common.collect.ForwardingCollection
add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray
 
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, iterator, remove, removeAll, retainAll, toString
 
Methods inherited from interface java.util.Collection
addAll, clear, isEmpty, size, toArray, toArray
 

Constructor Detail

ForwardingMultiset

public ForwardingMultiset()
Method Detail

delegate

protected abstract Multiset<E> delegate()
Description copied from class: ForwardingObject
Returns the backing delegate instance that methods are forwarded to. Abstract subclasses generally override this method with an abstract method that has a more specific return type, such as ForwardingSet.delegate(). Concrete subclasses override this method to supply the instance being decorated.

Specified by:
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 int 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 the element to add. May be zero, in which case no change will be made.
Returns:
the count of the element before the operation; possibly zero

remove

public int remove(Object element,
                  int occurrences)
Description copied from interface: Multiset
Removes a number of occurrences of the specified element from this multiset. If the multiset contains fewer than this number of occurrences to begin with, all occurrences will be removed. 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 the element to remove. May be zero, in which case no change will be made.
Returns:
the count of the element before the operation; 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(@Nullable
                      Object object)
Description copied from class: java.lang.Object
Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation on non-null object references:

The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).

Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.

Specified by:
equals in interface Multiset<E>
Specified by:
equals in interface Collection<E>
Overrides:
equals in class Object
Parameters:
object - the reference object with which to compare.
Returns:
true if this object is the same as the obj argument; false otherwise.
See Also:
Object.hashCode(), Hashtable

hashCode

public int hashCode()
Description copied from class: java.lang.Object
Returns a hash code value for the object. This method is supported for the benefit of hashtables such as those provided by java.util.Hashtable.

The general contract of hashCode is:

As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)

Specified by:
hashCode in interface Multiset<E>
Specified by:
hashCode in interface Collection<E>
Overrides:
hashCode in class Object
Returns:
a hash code value for this object.
See Also:
Object.equals(java.lang.Object), Hashtable

setCount

public int setCount(E element,
                    int count)
Description copied from interface: Multiset
Adds or removes the necessary occurrences of an element such that the element attains the desired count.

Specified by:
setCount in interface Multiset<E>
Parameters:
element - the element to add or remove occurrences of; may be null only if explicitly allowed by the implementation
count - the desired count of the element in this multiset
Returns:
the count of the element before the operation; possibly zero

setCount

public boolean setCount(E element,
                        int oldCount,
                        int newCount)
Description copied from interface: Multiset
Conditionally sets the count of an element to a new value, as described in Multiset.setCount(Object, int), provided that the element has the expected current count. If the current count is not oldCount, no change is made.

Specified by:
setCount in interface Multiset<E>
Parameters:
element - the element to conditionally set the count of; may be null only if explicitly allowed by the implementation
oldCount - the expected present count of the element in this multiset
newCount - the desired count of the element in this multiset
Returns:
true if the condition for modification was met. This implies that the multiset was indeed modified, unless oldCount == newCount.