java.util
Class ArrayList<E>

java.lang.Object
  java.util.AbstractCollection<E>
      java.util.AbstractList<E>
          java.util.ArrayList<E>

All Implemented Interfaces:

Serializable , Cloneable , Iterable <E>, Collection <E>, List <E>, RandomAccess

Direct Known Subclasses:

AttributeList , RoleList , RoleUnresolvedList

public class ArrayList<E>
extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, Serializable

Resizable-array implementation of the List interface. Implements all optional list operations, and permits all elements, including null . In addition to implementing the List interface, this class provides methods to manipulate the size of the array that is used internally to store the list. (This class is roughly equivalent to Vector , except that it is unsynchronized.)

The size , isEmpty , get , set , iterator , and listIterator operations run in constant time. The add operation runs in amortized constant time , that is, adding n elements requires O(n) time. All of the other operations run in linear time (roughly speaking). The constant factor is low compared to that for the LinkedList implementation.

Each ArrayList instance has a capacity . The capacity is the size of the array used to store the elements in the list. It is always at least as large as the list size. As elements are added to an ArrayList, its capacity grows automatically. The details of the growth policy are not specified beyond the fact that adding an element has constant amortized time cost.

An application can increase the capacity of an ArrayList instance before adding a large number of elements using the ensureCapacity operation. This may reduce the amount of incremental reallocation.

Note that this implementation is not synchronized. If multiple threads access an ArrayList instance concurrently, and at least one of the threads modifies the list structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more elements, or explicitly resizes the backing array; merely setting the value of an element is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the list. If no such object exists, the list should be "wrapped" using the Collections.synchronizedList Collections.synchronizedList method. This is best done at creation time, to prevent accidental unsynchronized access to the list:

        List list = Collections.synchronizedList(new ArrayList(...));
 

The iterators returned by this class's iterator and listIterator methods are fail-fast : if the list is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove or add methods, the iterator will throw a ConcurrentModificationException . ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.

This class is a member of the Java Collections Framework .

Since:

1.2

See Also:

Collection , List , LinkedList , Vector , Collections.synchronizedList(List) , Serialized Form

Field Summary

 

Fields inherited from class java.util. AbstractList
modCount

 

Constructor Summary
ArrayList ()           Constructs an empty list with an initial capacity of ten.
ArrayList ( Collection <? extends E > c)           Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.
ArrayList (int initialCapacity)           Constructs an empty list with the specified initial capacity.

 

Method Summary
boolean	add ( E           Appends the specified element to the end of this list.
void	add (int index, E  element)           Inserts the specified element at the specified position in this list.
boolean	addAll ( Collection <? extends E           Appends all of the elements in the specified collection Collection to the end of this list, in the order that they are returned by the specified collection's Collection's Iterator.
boolean	addAll (int index, Collection <? extends E           Inserts all of the elements in the specified collection Collection into this list, starting at the specified position.
void	clear ()           Removes all of the elements from this list.
Object	clone ()           Returns a shallow copy of this ArrayList instance.
boolean	contains ( Object           Returns true if this list contains the specified element.
void	ensureCapacity (int minCapacity)           Increases 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.
E	get (int index)           Returns the element at the specified position in this list.
int	indexOf ( Object           Returns           Searches for the index of the first occurrence occurence of the specified element in this list, or -1 if this list does not contain given argument, testing for equality using the element. equals method.
boolean	isEmpty ()           Returns true           Tests if this list contains has no elements.
int	lastIndexOf ( Object           Returns the index of the last occurrence of the specified element object in this list, or -1 if this list does not contain the element. list.
E	remove (int index)           Removes the element at the specified position in this list.
boolean	remove ( Object           Removes the first occurrence a single instance of the specified element from this list, if it is present. present (optional operation).
protected  void	removeRange (int fromIndex, int toIndex)           Removes from this list List all of the elements whose index is between fromIndex , inclusive, fromIndex, inclusive and toIndex , toIndex, exclusive.
E	set (int index, E  element)           Replaces the element at the specified position in this list with the specified element.
int	size ()           Returns the number of elements in this list.
Object	toArray ()           Returns an array containing all of the elements in this list in proper sequence (from first to last element). the correct order.
<T> T[]	toArray (T[] a)           Returns an array containing all of the elements in this list in proper sequence (from first to last element); the correct order; the runtime type of the returned array is that of the specified array.
void	trimToSize ()           Trims the capacity of this ArrayList instance to be the list's current size.

 

Methods inherited from class java.util. AbstractList
equals , hashCode , iterator , listIterator , listIterator , subList

 

Methods inherited from class java.util. AbstractCollection
containsAll , removeAll , retainAll , toString

 

Methods inherited from class java.lang. Object
finalize , getClass , notify , notifyAll , wait , wait , wait

 

Methods inherited from interface java.util. List
containsAll , equals , hashCode , iterator , listIterator , listIterator , removeAll , retainAll , subList

 

Constructor Detail

ArrayList

public ArrayList(int initialCapacity)

Constructs an empty list with the specified initial capacity.

Parameters:

initialCapacity - the initial capacity of the list list.

Throws:

IllegalArgumentException - if the specified initial capacity is negative

ArrayList

public ArrayList()

Constructs an empty list with an initial capacity of ten.

ArrayList

public ArrayList(Collection<? extends E> c)

Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator. The ArrayList instance has an initial capacity of 110% the size of the specified collection.

Parameters:

c - the collection whose elements are to be placed into this list list.

Throws:

NullPointerException - if the specified collection is null null.

trimToSize

public void trimToSize()

Trims 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.

ensureCapacity

public void ensureCapacity(int minCapacity)

Increases 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.

Parameters:

minCapacity - the desired minimum capacity capacity.

size

public int size()

Returns the number of elements in this list.

Specified by:

size in interface Collection < E >

Specified by:

size in interface List < E >

Specified by:

size in class AbstractCollection < E >

Returns:

the number of elements in this list list.

isEmpty

public boolean isEmpty()

Returns true Tests if this list contains has no elements.

Specified by:

isEmpty in interface Collection < E >

Specified by:

isEmpty in interface List < E >

Overrides:

isEmpty in class AbstractCollection < E >

Returns:

true if this list contains has no elements elements; false otherwise.

contains

public boolean contains(Object o)  elem) 

Returns true if this list contains the specified element. More formally, returns true if and only if this list contains at least one element e such that (o==null ? e==null : o.equals(e)) .

Specified by:

contains in interface Collection < E >

Specified by:

contains in interface List < E >

Overrides:

contains in class AbstractCollection < E >

Parameters:

o elem - element whose presence in this list List is to be tested tested.

Returns:

true if this list contains the specified element is present; false otherwise.

indexOf

public int indexOf(Object o)  elem) 

Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the lowest index Searches for the first occurence of the given argument, testing for equality using the i equals such that (o==null ? get(i)==null : o.equals(get(i))) , or -1 if there is no such index. method.

Specified by:

indexOf in interface List < E >

Overrides:

indexOf in class AbstractList < E >

Parameters:

o - element to search for elem - an object.

Returns:

the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element the index of the first occurrence of the argument in this list; returns -1 if the object is not found.

See Also:

Object.equals(Object)

lastIndexOf

public int lastIndexOf(Object o)  elem) 

Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the highest index i such that (o==null ? get(i)==null : o.equals(get(i))) , or -1 if there is no such index. Returns the index of the last occurrence of the specified object in this list.

Specified by:

lastIndexOf in interface List < E >

Overrides:

lastIndexOf in class AbstractList < E >

Parameters:

o - element to search for elem - the desired element.

Returns:

the index of the last occurrence of the specified element object in this list, or list; returns -1 if this list does the object is not contain the element found.

clone

public Object clone()

Returns a shallow copy of this ArrayList instance. (The elements themselves are not copied.)

Overrides:

clone in class Object

Returns:

a clone of this ArrayList instance instance.

See Also:

Cloneable

toArray

public Object[] toArray()

Returns an array containing all of the elements in this list in proper sequence (from first to last element). the correct order.

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

This method acts as bridge between array-based and collection-based APIs.

Specified by:

toArray in interface Collection < E >

Specified by:

toArray in interface List < E >

Overrides:

toArray in class AbstractCollection < E >

Returns:

an array containing all of the elements in this list in proper sequence the correct order.

See Also:

Arrays.asList(Object[])

toArray

public <T> T[] toArray(T[] a)

Returns an array containing all of the elements in this list in proper sequence (from first to last element); 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.

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

Specified by:

toArray in interface Collection < E >

Specified by:

toArray in interface List < E >

Overrides:

toArray in class AbstractCollection < E >

Parameters:

a - the array into which the elements of the list 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 the elements of the list list.

Throws:

ArrayStoreException - if the runtime type of the specified array a is not a supertype of the runtime type of every element in this list

NullPointerException - if the specified array is null list.

get

public E get(int index)

Returns the element at the specified position in this list.

Specified by:

get in interface List < E >

Specified by:

get in class AbstractList < E >

Parameters:

index - index of the element to return return.

Returns:

the element at the specified position in this list list.

Throws:

IndexOutOfBoundsException - if the index is out of range ( index (index < 0 || index >= size() size()) ) .

set

public E set(int index,
             E element)

Replaces the element at the specified position in this list with the specified element.

Specified by:

set in interface List < E >

Overrides:

set in class AbstractList < E >

Parameters:

index - index of the element to replace replace.

element - element to be stored at the specified position position.

Returns:

the element previously at the specified position position.

Throws:

IndexOutOfBoundsException - if the index is out of range ( index (index < 0 || index >= size() size()) ) .

add

public boolean add(E e)  o) 

Appends the specified element to the end of this list.

Specified by:

add in interface Collection < E >

Specified by:

add in interface List < E >

Overrides:

add in class AbstractList < E >

Parameters:

e o - element to be appended to this list list.

Returns:

true (as specified by Collection.add(E) ) (as per the general contract of Collection.add).

add

public void add(int index,
                E element)

Inserts the specified element at the specified position in this list. Shifts the element currently at that position (if any) and any subsequent elements to the right (adds one to their indices).

Specified by:

add in interface List < E >

Overrides:

add in class AbstractList < E >

Parameters:

index - index at which the specified element is to be inserted inserted.

element - element to be inserted inserted.

Throws:

IndexOutOfBoundsException - if the index is out of range ( index (index < 0 || index > size() size()) ) .

remove

public E remove(int index)

Removes the element at the specified position in this list. Shifts any subsequent elements to the left (subtracts one from their indices).

Specified by:

remove in interface List < E >

Overrides:

remove in class AbstractList < E >

Parameters:

index - the index of the element to be removed removed.

Returns:

the element that was removed from the list list.

Throws:

IndexOutOfBoundsException - if the index is out of range ( index (index < 0 || index >= size() size()) ) .

remove

public boolean remove(Object o)

Removes the first occurrence a single instance of the specified element from this list, if it is present. If the list does not contain the element, it is unchanged. present (optional operation). More formally, removes the an element with the lowest index i e such that (o==null ? get(i)==null : o.equals(get(i))) (o==null ? e==null : o.equals(e)) (if such an element exists). , if the list contains one or more such elements. Returns true if this the list contained the specified element (or equivalently, if this the list changed as a result of the call).

Specified by:

remove in interface Collection < E >

Specified by:

remove in interface List < E >

Overrides:

remove in class AbstractCollection < E >

Parameters:

o - element to be removed from this list, if present present.

Returns:

true if this the list contained the specified element element.

clear

public void clear()

Removes all of the elements from this list. The list will be empty after this call returns.

Specified by:

clear in interface Collection < E >

Specified by:

clear in interface List < E >

Overrides:

clear in class AbstractList < E >

addAll

public boolean addAll(Collection<? extends E> c)

Appends all of the elements in the specified collection Collection to the end of this list, in the order that they are returned by the specified collection's Collection's Iterator. The behavior of this operation is undefined if the specified collection Collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified collection Collection is this list, and this list is nonempty.)

Specified by:

addAll in interface Collection < E >

Specified by:

addAll in interface List < E >

Overrides:

addAll in class AbstractCollection < E >

Parameters:

c - collection containing the elements to be added to inserted into this list list.

Returns:

true if this list changed as a result of the call call.

Throws:

NullPointerException - if the specified collection is null null.

See Also:

AbstractCollection.add(Object)

addAll

public boolean addAll(int index,
                      Collection<? extends E> c)

Inserts all of the elements in the specified collection Collection into this list, starting at the specified position. Shifts the element currently at that position (if any) and any subsequent elements to the right (increases their indices). The new elements will appear in the list in the order that they are returned by the specified collection's Collection's iterator.

Specified by:

addAll in interface List < E >

Overrides:

addAll in class AbstractList < E >

Parameters:

index - index at which to insert the first element from the specified collection collection.

c - collection containing elements to be added to inserted into this list list.

Returns:

true if this list changed as a result of the call call.

Throws:

IndexOutOfBoundsException - if the index is out of range ( index (index < 0 || index > size() size()) ) .

NullPointerException - if the specified collection Collection is null null.

removeRange

protected void removeRange(int fromIndex,
                           int toIndex)

Removes from this list List all of the elements whose index is between fromIndex , inclusive, fromIndex, inclusive and toIndex , toIndex, exclusive. Shifts any succeeding elements to the left (reduces their index). This call shortens the list by (toIndex - fromIndex) elements. (If toIndex==fromIndex , this operation has no effect.)

Overrides:

removeRange in class AbstractList < E >

Parameters:

fromIndex - index of first element to be removed removed.

toIndex - index after last element to be removed

Throws:

IndexOutOfBoundsException - if fromIndex or toIndex out of range (fromIndex < 0 || fromIndex >= size() || toIndex > size() || toIndex < fromIndex) toIndex - index after last element to be removed.