Package org.apache.commons.collections

Class FastArrayList

  • All Implemented Interfaces:
    Serializable, Cloneable, Iterable, Collection, List, RandomAccess
    public class FastArrayList
extends ArrayList

    A customized implementation of java.util.ArrayList designed to operate in a multithreaded environment where the large majority of method calls are read-only, instead of structural changes. When operating in "fast" mode, read calls are non-synchronized and write calls perform the following steps:

    • Clone the existing collection
    • Perform the modification on the clone
    • Replace the existing collection with the (modified) clone

    When first created, objects of this class default to "slow" mode, where all accesses of any type are synchronized but no cloning takes place. This is appropriate for initially populating the collection, followed by a switch to "fast" mode (by calling setFast(true)) after initialization is complete.

    NOTE: If you are creating and accessing an ArrayList only within a single thread, you should use java.util.ArrayList directly (with no synchronization), for maximum performance.

    NOTE: This class is not cross-platform. Using it may cause unexpected failures on some architectures. It suffers from the same problems as the double-checked locking idiom. In particular, the instruction that clones the internal collection and the instruction that sets the internal reference to the clone can be executed or perceived out-of-order. This means that any read operation might fail unexpectedly, as it may be reading the state of the internal collection before the internal collection is fully formed. For more information on the double-checked locking idiom, see the Double-Checked Locking Idiom Is Broken Declaration.

    Since:
    Commons Collections 1.0
    Version:
    $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
    Author:
    Craig R. McClanahan, Stephen Colebourne
    See Also:
    Serialized Form

    • Field Summary

      Fields 
      Modifier and Type Field Description
      protected boolean fast
      Are we operating in "fast" mode?
      protected ArrayList list
      The underlying list we are managing.

    • Constructor Summary

      Constructors 
      Constructor Description
      FastArrayList()
      Construct a an empty list.
      FastArrayList​(int capacity)
      Construct an empty list with the specified capacity.
      FastArrayList​(Collection collection)
      Construct a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void add​(int index, Object element)
      Insert the specified element at the specified position in this list, and shift all remaining elements up one position.
      boolean add​(Object element)
      Appends the specified element to the end of this list.
      boolean addAll​(int index, Collection collection)
      Insert all of the elements in the specified Collection at the specified position in this list, and shift any previous elements upwards as needed.
      boolean addAll​(Collection collection)
      Append all of the elements in the specified Collection to the end of this list, in the order that they are returned by the specified Collection's Iterator.
      void clear()
      Remove all of the elements from this list.
      Object clone()
      Return a shallow copy of this FastArrayList instance.
      boolean contains​(Object element)
      Return true if this list contains the specified element.
      boolean containsAll​(Collection collection)
      Return true if this list contains all of the elements in the specified Collection.
      void ensureCapacity​(int capacity)
      Increase the capacity of this ArrayList instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.
      boolean equals​(Object o)
      Compare the specified object with this list for equality.
      Object get​(int index)
      Return the element at the specified position in the list.
      boolean getFast()
      Returns true if this list is operating in fast mode.
      int hashCode()
      Return the hash code value for this list.
      int indexOf​(Object element)
      Search for the first occurrence of the given argument, testing for equality using the equals() method, and return the corresponding index, or -1 if the object is not found.
      boolean isEmpty()
      Test if this list has no elements.
      Iterator iterator()
      Return an iterator over the elements in this list in proper sequence.
      int lastIndexOf​(Object element)
      Search for the last occurrence of the given argument, testing for equality using the equals() method, and return the corresponding index, or -1 if the object is not found.
      ListIterator listIterator()
      Return an iterator of the elements of this list, in proper sequence.
      ListIterator listIterator​(int index)
      Return an iterator of the elements of this list, in proper sequence, starting at the specified position.
      Object remove​(int index)
      Remove the element at the specified position in the list, and shift any subsequent elements down one position.
      boolean remove​(Object element)
      Remove the first occurrence of the specified element from the list, and shift any subsequent elements down one position.
      boolean removeAll​(Collection collection)
      Remove from this collection all of its elements that are contained in the specified collection.
      boolean retainAll​(Collection collection)
      Remove from this collection all of its elements except those that are contained in the specified collection.
      Object set​(int index, Object element)
      Replace the element at the specified position in this list with the specified element.
      void setFast​(boolean fast)
      Sets whether this list will operate in fast mode.
      int size()
      Return the number of elements in this list.
      List subList​(int fromIndex, int toIndex)
      Return a view of the portion of this list between fromIndex (inclusive) and toIndex (exclusive).
      Object[] toArray()
      Return an array containing all of the elements in this list in the correct order.
      Object[] toArray​(Object[] array)
      Return an array containing all of the elements in this list in the correct order.
      String toString()
      Return a String representation of this object.
      void trimToSize()
      Trim the capacity of this ArrayList instance to be the list's current size.

    • Field Detail

      • list

        protected ArrayList list
        The underlying list we are managing.

      • fast

        protected boolean fast
        Are we operating in "fast" mode?

    • Constructor Detail

      • FastArrayList

        public FastArrayList()
        Construct a an empty list.

      • FastArrayList

        public FastArrayList​(int capacity)
        Construct an empty list with the specified capacity.
        Parameters:
        capacity - The initial capacity of the empty list

      • FastArrayList

        public FastArrayList​(Collection collection)
        Construct a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.
        Parameters:
        collection - The collection whose elements initialize the contents of this list

    • Method Detail

      • getFast

        public boolean getFast()
        Returns true if this list is operating in fast mode.
        Returns:
        true if this list is operating in fast mode

      • setFast

        public void setFast​(boolean fast)
        Sets whether this list will operate in fast mode.
        Parameters:
        fast - true if the list should operate in fast mode

      • add

        public boolean add​(Object element)
        Appends the specified element to the end of this list.
        Specified by:
        add in interface Collection
        Specified by:
        add in interface List
        Overrides:
        add in class ArrayList
        Parameters:
        element - The element to be appended

      • add

        public void add​(int index,
                Object element)
        Insert the specified element at the specified position in this list, and shift all remaining elements up one position.
        Specified by:
        add in interface List
        Overrides:
        add in class ArrayList
        Parameters:
        index - Index at which to insert this element
        element - The element to be inserted
        Throws:
        IndexOutOfBoundsException - if the index is out of range

      • addAll

        public boolean addAll​(Collection collection)
        Append all of the elements in the specified Collection to the end of this list, in the order that they are returned by the specified Collection's Iterator.
        Specified by:
        addAll in interface Collection
        Specified by:
        addAll in interface List
        Overrides:
        addAll in class ArrayList
        Parameters:
        collection - The collection to be appended

      • addAll

        public boolean addAll​(int index,
                      Collection collection)
        Insert all of the elements in the specified Collection at the specified position in this list, and shift any previous elements upwards as needed.
        Specified by:
        addAll in interface List
        Overrides:
        addAll in class ArrayList
        Parameters:
        index - Index at which insertion takes place
        collection - The collection to be added
        Throws:
        IndexOutOfBoundsException - if the index is out of range

      • clone

        public Object clone()
        Return a shallow copy of this FastArrayList instance. The elements themselves are not copied.
        Overrides:
        clone in class ArrayList

      • contains

        public boolean contains​(Object element)
        Return true if this list contains the specified element.
        Specified by:
        contains in interface Collection
        Specified by:
        contains in interface List
        Overrides:
        contains in class ArrayList
        Parameters:
        element - The element to test for

      • ensureCapacity

        public void ensureCapacity​(int capacity)
        Increase the capacity of this ArrayList instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.
        Overrides:
        ensureCapacity in class ArrayList
        Parameters:
        capacity - The new minimum capacity

      • equals

        public boolean equals​(Object o)
        Compare the specified object with this list for equality. This implementation uses exactly the code that is used to define the list equals function in the documentation for the List.equals method.
        Specified by:
        equals in interface Collection
        Specified by:
        equals in interface List
        Overrides:
        equals in class ArrayList
        Parameters:
        o - Object to be compared to this list

      • get

        public Object get​(int index)
        Return the element at the specified position in the list.
        Specified by:
        get in interface List
        Overrides:
        get in class ArrayList
        Parameters:
        index - The index of the element to return
        Throws:
        IndexOutOfBoundsException - if the index is out of range

      • hashCode

        public int hashCode()
        Return the hash code value for this list. This implementation uses exactly the code that is used to define the list hash function in the documentation for the List.hashCode method.
        Specified by:
        hashCode in interface Collection
        Specified by:
        hashCode in interface List
        Overrides:
        hashCode in class ArrayList

      • indexOf

        public int indexOf​(Object element)
        Search for the first occurrence of the given argument, testing for equality using the equals() method, and return the corresponding index, or -1 if the object is not found.
        Specified by:
        indexOf in interface List
        Overrides:
        indexOf in class ArrayList
        Parameters:
        element - The element to search for

      • iterator

        public Iterator iterator()
        Return an iterator over the elements in this list in proper sequence.

        Thread safety
        The iterator returned is thread-safe ONLY in FAST mode. In slow mode there is no way to synchronize, or make the iterator thread-safe.

        In fast mode iteration and modification may occur in parallel on different threads, however there is a restriction. Modification must be EITHER via the Iterator interface methods OR the List interface. If a mixture of modification methods is used a ConcurrentModificationException is thrown from the iterator modification method. If the List modification methods are used the changes are NOT visible in the iterator (it shows the list contents at the time the iterator was created).

        Specified by:
        iterator in interface Collection
        Specified by:
        iterator in interface Iterable
        Specified by:
        iterator in interface List
        Overrides:
        iterator in class ArrayList
        Returns:
        the iterator

      • lastIndexOf

        public int lastIndexOf​(Object element)
        Search for the last occurrence of the given argument, testing for equality using the equals() method, and return the corresponding index, or -1 if the object is not found.
        Specified by:
        lastIndexOf in interface List
        Overrides:
        lastIndexOf in class ArrayList
        Parameters:
        element - The element to search for

      • listIterator

        public ListIterator listIterator()
        Return an iterator of the elements of this list, in proper sequence.

        Thread safety
        The iterator returned is thread-safe ONLY in FAST mode. In slow mode there is no way to synchronize, or make the iterator thread-safe.

        In fast mode iteration and modification may occur in parallel on different threads, however there is a restriction. Modification must be EITHER via the Iterator interface methods OR the List interface. If a mixture of modification methods is used a ConcurrentModificationException is thrown from the iterator modification method. If the List modification methods are used the changes are NOT visible in the iterator (it shows the list contents at the time the iterator was created).

        Specified by:
        listIterator in interface List
        Overrides:
        listIterator in class ArrayList
        Returns:
        the list iterator

      • listIterator

        public ListIterator listIterator​(int index)
        Return an iterator of the elements of this list, in proper sequence, starting at the specified position.

        Thread safety
        The iterator returned is thread-safe ONLY in FAST mode. In slow mode there is no way to synchronize, or make the iterator thread-safe.

        In fast mode iteration and modification may occur in parallel on different threads, however there is a restriction. Modification must be EITHER via the Iterator interface methods OR the List interface. If a mixture of modification methods is used a ConcurrentModificationException is thrown from the iterator modification method. If the List modification methods are used the changes are NOT visible in the iterator (it shows the list contents at the time the iterator was created).

        Specified by:
        listIterator in interface List
        Overrides:
        listIterator in class ArrayList
        Parameters:
        index - The starting position of the iterator to return
        Returns:
        the list iterator
        Throws:
        IndexOutOfBoundsException - if the index is out of range

      • remove

        public Object remove​(int index)
        Remove the element at the specified position in the list, and shift any subsequent elements down one position.
        Specified by:
        remove in interface List
        Overrides:
        remove in class ArrayList
        Parameters:
        index - Index of the element to be removed
        Throws:
        IndexOutOfBoundsException - if the index is out of range

      • remove

        public boolean remove​(Object element)
        Remove the first occurrence of the specified element from the list, and shift any subsequent elements down one position.
        Specified by:
        remove in interface Collection
        Specified by:
        remove in interface List
        Overrides:
        remove in class ArrayList
        Parameters:
        element - Element to be removed

      • removeAll

        public boolean removeAll​(Collection collection)
        Remove from this collection all of its elements that are contained in the specified collection.
        Specified by:
        removeAll in interface Collection
        Specified by:
        removeAll in interface List
        Overrides:
        removeAll in class ArrayList
        Parameters:
        collection - Collection containing elements to be removed
        Throws:
        UnsupportedOperationException - if this optional operation is not supported by this list

      • retainAll

        public boolean retainAll​(Collection collection)
        Remove from this collection all of its elements except those that are contained in the specified collection.
        Specified by:
        retainAll in interface Collection
        Specified by:
        retainAll in interface List
        Overrides:
        retainAll in class ArrayList
        Parameters:
        collection - Collection containing elements to be retained
        Throws:
        UnsupportedOperationException - if this optional operation is not supported by this list

      • set

        public Object set​(int index,
                  Object element)
        Replace the element at the specified position in this list with the specified element. Returns the previous object at that position.

        IMPLEMENTATION NOTE - This operation is specifically documented to not be a structural change, so it is safe to be performed without cloning.
        Specified by:
        set in interface List
        Overrides:
        set in class ArrayList
        Parameters:
        index - Index of the element to replace
        element - The new element to be stored
        Throws:
        IndexOutOfBoundsException - if the index is out of range

      • size

        public int size()
        Return the number of elements in this list.
        Specified by:
        size in interface Collection
        Specified by:
        size in interface List
        Overrides:
        size in class ArrayList

      • subList

        public List subList​(int fromIndex,
                    int toIndex)
        Return a view of the portion of this list between fromIndex (inclusive) and toIndex (exclusive). The returned list is backed by this list, so non-structural changes in the returned list are reflected in this list. The returned list supports all of the optional list operations supported by this list.
        Specified by:
        subList in interface List
        Overrides:
        subList in class ArrayList
        Parameters:
        fromIndex - The starting index of the sublist view
        toIndex - The index after the end of the sublist view
        Throws:
        IndexOutOfBoundsException - if an index is out of range

      • toArray

        public Object[] toArray​(Object[] array)
        Return an array containing all of the elements in this list in the correct order. The runtime type of the returned array is that of the specified array. If the list 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 list.
        Specified by:
        toArray in interface Collection
        Specified by:
        toArray in interface List
        Overrides:
        toArray in class ArrayList
        Parameters:
        array - Array defining the element type of the returned list
        Throws:
        ArrayStoreException - if the runtime type of array is not a supertype of the runtime type of every element in this list

      • trimToSize

        public void trimToSize()
        Trim the capacity of this ArrayList instance to be the list's current size. An application can use this operation to minimize the storage of an ArrayList instance.
        Overrides:
        trimToSize in class ArrayList