Package com.google.common.collect

Class ConcurrentHashMultiset<E>

    • Nested Class Summary

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods Deprecated Methods 
      Modifier and Type Method Description
      boolean add​(@Nullable E element)
      Ensures that this collection contains the specified element (optional operation).
      int add​(E element, int occurrences)
      Adds a number of occurrences of the specified element to this multiset.
      boolean addAll​(Collection<? extends E> elementsToAdd)
      Adds all of the elements in the specified collection to this collection (optional operation).
      void clear()
      Removes all of the elements from this collection (optional operation).
      boolean contains​(@Nullable Object element)
      Returns true if this collection contains the specified element.
      int count​(@Nullable Object element)
      Returns the number of occurrences of element in this multiset.
      static <E> ConcurrentHashMultiset<E> create()
      Creates a new, empty ConcurrentHashMultiset using the default initial capacity, load factor, and concurrency settings.
      static <E> ConcurrentHashMultiset<E> create​(Iterable<? extends E> elements)
      Creates a new ConcurrentHashMultiset containing the specified elements, using the default initial capacity, load factor, and concurrency settings.
      static <E> ConcurrentHashMultiset<E> create​(ConcurrentMap<E,​AtomicInteger> countMap)
      Creates a new, empty ConcurrentHashMultiset using countMap as the internal backing map.
      Set<Multiset.Entry<E>> createEntrySet()
      Deprecated.
      Internal method, use Multiset.entrySet().
      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​(@Nullable Object object)
      Indicates whether some other object is "equal to" this one.
      int hashCode()
      Returns a hash code value for the object.
      boolean isEmpty()
      Returns true if this collection contains no elements.
      Iterator<E> iterator()
      Returns an iterator over the elements contained in this collection.
      boolean remove​(@Nullable Object element)
      Removes a single instance of the specified element from this collection, if it is present (optional operation).
      int remove​(@Nullable Object element, int occurrences)
      Removes a number of occurrences of the specified element from this multiset.
      boolean removeAll​(Collection<?> elementsToRemove)
      Removes all of this collection's elements that are also contained in the specified collection (optional operation).
      boolean removeExactly​(@Nullable Object element, int occurrences)
      Removes exactly the specified number of occurrences of element, or makes no change if this is not possible.
      boolean retainAll​(Collection<?> elementsToRetain)
      Retains only the elements in this collection that are contained in the specified collection (optional operation).
      int setCount​(E element, int count)
      Adds or removes occurrences of element such that the count(java.lang.Object) of the element becomes count.
      boolean setCount​(E element, int expectedOldCount, int newCount)
      Sets the number of occurrences of element to newCount, but only if the count is currently expectedOldCount.
      int size()
      Returns the number of elements in this collection.
      Object[] toArray()
      Returns an array containing all of the elements in this collection.
      <T> T[] toArray​(T[] array)
      Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.
      String toString()
      Returns a string representation of this collection.

    • Method Detail

      • create

        public static <E> ConcurrentHashMultiset<E> create()
        Creates a new, empty ConcurrentHashMultiset using the default initial capacity, load factor, and concurrency settings.

      • create

        public static <E> ConcurrentHashMultiset<E> create​(Iterable<? extends E> elements)
        Creates a new ConcurrentHashMultiset containing the specified elements, using the default initial capacity, load factor, and concurrency settings.

        This implementation is highly efficient when elements is itself a Multiset.

        Parameters:
        elements - the elements that the multiset should contain

      • create

        @Beta
public static <E> ConcurrentHashMultiset<E> create​(ConcurrentMap<E,​AtomicInteger> countMap)
        Creates a new, empty ConcurrentHashMultiset using countMap as the internal backing map.

        This instance will assume ownership of countMap, and other code should not maintain references to the map or modify it in any way.

        The returned multiset is serializable if the input map is.

        Parameters:
        countMap - backing map for storing the elements in the multiset and their counts. It must be empty.
        Throws:
        IllegalArgumentException - if countMap is not empty
        Since:
        20.0

      • count

        public int count​(@Nullable Object element)
        Returns the number of occurrences of element in this multiset.
        Specified by:
        count in interface Multiset<E>
        Parameters:
        element - the element to look for
        Returns:
        the nonnegative number of occurrences of the element

      • size

        public int size()
        Returns the number of elements in this collection. If this collection contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

        If the data in the multiset is modified by any other threads during this method, it is undefined which (if any) of these modifications will be reflected in the result.

        Specified by:
        size in interface Collection<E>
        Specified by:
        size in interface Multiset<E>
        Specified by:
        size in class AbstractCollection<E>
        Returns:
        the number of elements in this collection

      • toArray

        public Object[] toArray()
        Description copied from class: java.util.AbstractCollection
        Returns an array containing all of the elements in this collection. If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order. The returned array's runtime component type is Object.

        The returned array will be "safe" in that no references to it are maintained by this collection. (In other words, this method must allocate a new array even if this collection is backed by an array). The caller is thus free to modify the returned array.

        Specified by:
        toArray in interface Collection<E>
        Overrides:
        toArray in class AbstractCollection<E>
        Returns:
        an array, whose runtime component type is Object, containing all of the elements in this collection

      • toArray

        public <T> T[] toArray​(T[] array)
        Description copied from class: java.util.AbstractCollection
        Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. If the collection fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this collection.

        If this collection fits in the specified array with room to spare (i.e., the array has more elements than this collection), the element in the array immediately following the end of the collection is set to null. (This is useful in determining the length of this collection only if the caller knows that this collection does not contain any null elements.)

        If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.

        Specified by:
        toArray in interface Collection<E>
        Overrides:
        toArray in class AbstractCollection<E>
        Type Parameters:
        T - the component type of the array to contain the collection
        Parameters:
        array - the array into which the elements of this collection are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.
        Returns:
        an array containing all of the elements in this collection

      • add

        @CanIgnoreReturnValue
public int add​(E element,
               int occurrences)
        Adds a number of occurrences of the specified element to this multiset.
        Specified by:
        add in interface Multiset<E>
        Parameters:
        element - the element to add
        occurrences - the number of occurrences to add
        Returns:
        the previous count of the element before the operation; possibly zero
        Throws:
        IllegalArgumentException - if occurrences is negative, or if the resulting amount would exceed Integer.MAX_VALUE

      • remove

        @CanIgnoreReturnValue
public int remove​(@Nullable Object element,
                  int occurrences)
        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.
        Specified by:
        remove in interface Multiset<E>
        Parameters:
        element - the element whose occurrences should be removed
        occurrences - the number of occurrences of the element to remove
        Returns:
        the count of the element before the operation; possibly zero
        Throws:
        IllegalArgumentException - if occurrences is negative

      • removeExactly

        @CanIgnoreReturnValue
public boolean removeExactly​(@Nullable Object element,
                             int occurrences)
        Removes exactly the specified number of occurrences of element, or makes no change if this is not possible.

        This method, in contrast to remove(Object, int), has no effect when the element count is smaller than occurrences.

        Parameters:
        element - the element to remove
        occurrences - the number of occurrences of element to remove
        Returns:
        true if the removal was possible (including if occurrences is zero)
        Throws:
        IllegalArgumentException - if occurrences is negative

      • setCount

        @CanIgnoreReturnValue
public int setCount​(E element,
                    int count)
        Adds or removes occurrences of element such that the count(java.lang.Object) of the element becomes 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 element in the multiset before this call
        Throws:
        IllegalArgumentException - if count is negative

      • setCount

        @CanIgnoreReturnValue
public boolean setCount​(E element,
                        int expectedOldCount,
                        int newCount)
        Sets the number of occurrences of element to newCount, but only if the count is currently expectedOldCount. If element does not appear in the multiset exactly expectedOldCount times, no changes will be 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
        expectedOldCount - the expected present count of the element in this multiset
        newCount - the desired count of the element in this multiset
        Returns:
        true if the change was successful. This usually indicates that the multiset has been modified, but not always: in the case that expectedOldCount == newCount, the method will return true if the condition was met.
        Throws:
        IllegalArgumentException - if expectedOldCount or newCount is negative

      • clear

        public void clear()
        Description copied from class: java.util.AbstractCollection
        Removes all of the elements from this collection (optional operation). The collection will be empty after this method returns.
        Specified by:
        clear in interface Collection<E>

      • contains

        public boolean contains​(@Nullable Object element)
        Description copied from class: java.util.AbstractCollection
        Returns true if this collection contains the specified element. More formally, returns true if and only if this collection contains at least one element e such that Objects.equals(o, e).
        Specified by:
        contains in interface Collection<E>
        Specified by:
        contains in interface Multiset<E>
        Overrides:
        contains in class AbstractCollection<E>
        Parameters:
        element - element whose presence in this collection is to be tested
        Returns:
        true if this collection contains the specified element

      • add

        @CanIgnoreReturnValue
public final boolean add​(@Nullable E element)
        Description copied from class: java.util.AbstractCollection
        Ensures that this collection contains the specified element (optional operation). Returns true if this collection changed as a result of the call. (Returns false if this collection does not permit duplicates and already contains the specified element.)

        Collections that support this operation may place limitations on what elements may be added to this collection. In particular, some collections will refuse to add null elements, and others will impose restrictions on the type of elements that may be added. Collection classes should clearly specify in their documentation any restrictions on what elements may be added.

        If a collection refuses to add a particular element for any reason other than that it already contains the element, it must throw an exception (rather than returning false). This preserves the invariant that a collection always contains the specified element after this call returns.

        Specified by:
        add in interface Collection<E>
        Specified by:
        add in interface Multiset<E>
        Overrides:
        add in class AbstractCollection<E>
        Parameters:
        element - element whose presence in this collection is to be ensured
        Returns:
        true if this collection changed as a result of the call

      • remove

        @CanIgnoreReturnValue
public final boolean remove​(@Nullable Object element)
        Description copied from class: java.util.AbstractCollection
        Removes a single instance of the specified element from this collection, if it is present (optional operation). More formally, removes an element e such that Objects.equals(o, e), if this collection contains one or more such elements. Returns true if this collection contained the specified element (or equivalently, if this collection changed as a result of the call).
        Specified by:
        remove in interface Collection<E>
        Specified by:
        remove in interface Multiset<E>
        Overrides:
        remove in class AbstractCollection<E>
        Parameters:
        element - element to be removed from this collection, if present
        Returns:
        true if an element was removed as a result of this call

      • addAll

        @CanIgnoreReturnValue
public final boolean addAll​(Collection<? extends E> elementsToAdd)
        Adds all of the elements in the specified collection to this collection (optional operation). The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified collection is this collection, and this collection is nonempty.)

        This implementation is highly efficient when elementsToAdd is itself a Multiset.

        Specified by:
        addAll in interface Collection<E>
        Overrides:
        addAll in class AbstractCollection<E>
        Parameters:
        elementsToAdd - collection containing elements to be added to this collection
        Returns:
        true if this collection changed as a result of the call
        See Also:
        AbstractCollection.add(Object)

      • 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 final boolean equals​(@Nullable Object 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.

        This implementation returns true if object is a multiset of the same size and if, for each element, the two multisets have the same count.

        Specified by:
        equals in interface Collection<E>
        Specified by:
        equals in interface Multiset<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(), HashMap

      • hashCode

        public final int hashCode()
        Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by HashMap.

        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 hash tables.

        As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (The hashCode may or may not be implemented as some function of an object's memory address at some point in time.)

        This implementation returns the hash code of Multiset.entrySet().

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

      • toString

        public final String toString()
        Returns a string representation of this collection. The string representation consists of a list of the collection's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (comma and space). Elements are converted to strings as by String.valueOf(Object).

        This implementation returns the result of invoking toString on Multiset.entrySet().

        Specified by:
        toString in interface Multiset<E>
        Overrides:
        toString in class AbstractCollection<E>
        Returns:
        a string representation of this collection