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

java.lang.Object
  com.google.common.collect.ForwardingObject
      com.google.common.collect.ForwardingCollection<E>
          com.google.common.collect.ForwardingMultiset<E>

All Implemented Interfaces:

Multiset<E>, Iterable<E>, Collection<E>

@GwtCompatible
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.

Warning: The methods of ForwardingMultiset forward indiscriminately to the methods of the delegate. For example, overriding add(Object, int) alone will not change the behavior of ForwardingCollection.add(Object), which can lead to unexpected behavior. In this case, you should override add(Object) as well, either providing your own implementation, or delegating to the provided standardAdd method.

The standard methods and any collection views they return are not guaranteed to be thread-safe, even when all of the methods that they depend on are thread-safe.

Since:

2 (imported from Google Collections Library)

Author:

Kevin Bourrillion, Louis Wasserman

ForwardingMultiset

protected ForwardingMultiset()

Constructor for use by subclasses.

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:

• It is reflexive: for any non-null reference value x, x.equals(x) should return true.
• It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
• It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
• It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
• For any non-null reference value x, x.equals(null) should return false.

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:

• Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
• If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
• It is not required that if two objects are unequal according to the Object.equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hashtables.

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 Java^TM 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.

standardContains

@Beta
protected boolean standardContains(@Nullable
                                        Object object)

A sensible definition of ForwardingCollection.contains(java.lang.Object) in terms of count(java.lang.Object). If you override count(java.lang.Object), you may wish to override ForwardingCollection.contains(java.lang.Object) to forward to this implementation.

Overrides:

standardContains in class ForwardingCollection<E>

Since:

7

standardClear

@Beta
protected void standardClear()

A sensible definition of ForwardingCollection.clear() in terms of the iterator method of entrySet(). If you override entrySet(), you may wish to override ForwardingCollection.contains(java.lang.Object) to forward to this implementation.

Overrides:

standardClear in class ForwardingCollection<E>

Since:

7

standardCount

@Beta
protected int standardCount(@Nullable
                                 Object object)

A sensible, albeit inefficient, definition of count(java.lang.Object) in terms of entrySet(). If you override entrySet(), you may wish to override count(java.lang.Object) to forward to this implementation.

Since:

7

standardAdd

@Beta
protected boolean standardAdd(E element)

A sensible definition of ForwardingCollection.add(Object) in terms of add(Object, int). If you override add(Object, int), you may wish to override ForwardingCollection.add(Object) to forward to this implementation.

Since:

7

standardAddAll

@Beta
protected boolean standardAddAll(Collection<? extends E> elementsToAdd)

A sensible definition of ForwardingCollection.addAll(Collection) in terms of ForwardingCollection.add(Object) and add(Object, int). If you override either of these methods, you may wish to override ForwardingCollection.addAll(Collection) to forward to this implementation.

Overrides:

standardAddAll in class ForwardingCollection<E>

Since:

7

standardRemove

@Beta
protected boolean standardRemove(Object element)

A sensible definition of ForwardingCollection.remove(Object) in terms of remove(Object, int). If you override remove(Object, int), you may wish to override ForwardingCollection.remove(Object) to forward to this implementation.

Overrides:

standardRemove in class ForwardingCollection<E>

Since:

7

standardRemoveAll

@Beta
protected boolean standardRemoveAll(Collection<?> elementsToRemove)

A sensible definition of ForwardingCollection.removeAll(java.util.Collection) in terms of the removeAll method of elementSet(). If you override elementSet(), you may wish to override ForwardingCollection.removeAll(java.util.Collection) to forward to this implementation.

Overrides:

standardRemoveAll in class ForwardingCollection<E>

Since:

7

standardRetainAll

@Beta
protected boolean standardRetainAll(Collection<?> elementsToRetain)

A sensible definition of ForwardingCollection.retainAll(java.util.Collection) in terms of the retainAll method of elementSet(). If you override elementSet(), you may wish to override ForwardingCollection.retainAll(java.util.Collection) to forward to this implementation.

Overrides:

standardRetainAll in class ForwardingCollection<E>

Since:

7

standardSetCount

@Beta
protected int standardSetCount(E element,
                                    int count)

A sensible definition of setCount(Object, int) in terms of count(Object), add(Object, int), and remove(Object, int). entrySet(). If you override any of these methods, you may wish to override setCount(Object, int) to forward to this implementation.

Since:

7

standardSetCount

@Beta
protected boolean standardSetCount(E element,
                                        int oldCount,
                                        int newCount)

A sensible definition of setCount(Object, int, int) in terms of count(Object) and setCount(Object, int). If you override either of these methods, you may wish to override setCount(Object, int, int) to forward to this implementation.

Since:

7

standardElementSet

@Beta
protected Set<E> standardElementSet()

A sensible definition of elementSet() in terms of the following methods: ForwardingCollection.clear(), ForwardingCollection.contains(java.lang.Object), ForwardingCollection.containsAll(java.util.Collection), count(java.lang.Object), ForwardingCollection.isEmpty(), the size() and iterator() methods of entrySet(), and remove(Object, int). In many situations, you may wish to override elementSet() to forward to this implementation.

Since:

7

standardIterator

@Beta
protected Iterator<E> standardIterator()

A sensible definition of ForwardingCollection.iterator() in terms of entrySet() and ForwardingCollection.remove(Object). If you override either of these methods, you may wish to override ForwardingCollection.iterator() to forward to this implementation.

Since:

7

standardSize

@Beta
protected int standardSize()

A sensible, albeit inefficient, definition of ForwardingCollection.size() in terms of entrySet(). If you override entrySet(), you may wish to override ForwardingCollection.size() to forward to this implementation.

Since:

7

standardEquals

@Beta
protected boolean standardEquals(@Nullable
                                      Object object)

A sensible, albeit inefficient, definition of ForwardingCollection.size() in terms of entrySet().size() and count(java.lang.Object). If you override either of these methods, you may wish to override ForwardingCollection.size() to forward to this implementation.

Since:

7

standardHashCode

@Beta
protected int standardHashCode()

A sensible definition of hashCode() as entrySet().hashCode() . If you override entrySet(), you may wish to override hashCode() to forward to this implementation.

Since:

7

standardToString

@Beta
protected String standardToString()

A sensible definition of ForwardingObject.toString() as entrySet().toString() . If you override entrySet(), you may wish to override ForwardingObject.toString() to forward to this implementation.

Overrides:

standardToString in class ForwardingCollection<E>

Since:

7