org.apache.commons.collections

## Class FastArrayList

- java.lang.Object
- - java.util.AbstractCollection
  - - java.util.AbstractList
    - - java.util.ArrayList
      - - org.apache.commons.collections.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 and Description
    --- | ---
    `protected boolean` | `fast` Are we operating in "fast" mode?
    `protected ArrayList` | `list` The underlying list we are managing.

    - ### Fields inherited from class java.util.AbstractList

      `modCount`

  - ### Constructor Summary

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

  - ### Method Summary

    Methods
    Modifier and Type | Method and 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(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.
    `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.
    `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.

    - ### Methods inherited from class java.util.ArrayList

      `removeRange`

    - ### Methods inherited from class java.lang.Object

      `finalize, getClass, notify, notifyAll, wait, wait, wait`

- - ### 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

    - #### clear

          public void clear()

      Remove all of the elements from this list. The list will be empty after this call returns.
      Specified by:
        `clear` in interface `Collection`
      Specified by:
        `clear` in interface `List`
      Overrides:
        `clear` in class `ArrayList`
      Throws:
        `UnsupportedOperationException` - if `clear()` is not supported by this list

    - #### 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

    - #### containsAll

          public boolean containsAll(Collection collection)

      Return `true` if this list contains all of the elements in the specified Collection.
      Specified by:
        `containsAll` in interface `Collection`
      Specified by:
        `containsAll` in interface `List`
      Overrides:
        `containsAll` in class `AbstractCollection`
      Parameters:
        `collection` - Collection whose elements are to be checked

    - #### 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 `AbstractList`
      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 `AbstractList`

    - #### 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

    - #### isEmpty

          public boolean isEmpty()

      Test if this list has no elements.
      Specified by:
        `isEmpty` in interface `Collection`
      Specified by:
        `isEmpty` in interface `List`
      Overrides:
        `isEmpty` in class `ArrayList`

    - #### 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 `Iterable`
      Specified by:
        `iterator` in interface `Collection`
      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()

      Return an array containing all of the elements in this list in the correct order.
      Specified by:
        `toArray` in interface `Collection`
      Specified by:
        `toArray` in interface `List`
      Overrides:
        `toArray` in class `ArrayList`

    - #### 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

    - #### toString

          public String toString()

      Return a String representation of this object.
      Overrides:
        `toString` in class `AbstractCollection`

    - #### 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`

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