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Java Platform 1.2 |
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java.lang.Object
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+--java.util.AbstractCollection
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+--java.util.AbstractList
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+--java.util.ArrayList
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 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 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 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. 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.
Collection,
List,
LinkedList,
Vector,
Collections.synchronizedList(List), Serialized Form| Fields inherited from class java.util.AbstractList |
modCount |
| Constructor Summary | |
ArrayList()
Constructs an empty list. |
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ArrayList(Collection c)
Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator. |
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ArrayList(int initialCapacity)
Constructs an empty list with the specified initial capacity. |
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| Method Summary | |
void |
add(int index,
Object element)
Inserts the specified element at the specified position in this list. |
boolean |
add(Object o)
Appends the specified element to the end of this list. |
boolean |
addAll(Collection c)
Appends 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 c)
Inserts all of the elements in the specified 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 elem)
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. |
Object |
get(int index)
Returns the element at the specified position in this list. |
int |
indexOf(Object elem)
Searches for the first occurence of the given argument, testing for equality using the equals method. |
boolean |
isEmpty()
Tests if this list has no elements. |
int |
lastIndexOf(Object elem)
Returns the index of the last occurrence of the specified object in this list. |
Object |
remove(int index)
Removes the element at the specified position in this list. |
protected void |
removeRange(int fromIndex,
int toIndex)
Removes from this List all of the elements whose index is between fromIndex, inclusive and toIndex, exclusive. |
Object |
set(int index,
Object 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 the correct order. |
Object[] |
toArray(Object[] a)
Returns an array containing all of the elements in this list in the correct order. |
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,
remove,
removeAll,
retainAll,
toString |
| Methods inherited from class java.lang.Object |
finalize,
getClass,
notify,
notifyAll,
wait,
wait,
wait |
| Constructor Detail |
public ArrayList(int initialCapacity)
initialCapacity - the initial capacity of the list.public ArrayList()
public ArrayList(Collection c)
| Method Detail |
public void trimToSize()
public void ensureCapacity(int minCapacity)
minCapacity - the desired minimum capacity.public int size()
public boolean isEmpty()
public boolean contains(Object elem)
o - element whose presence in this List is to be tested.public int indexOf(Object elem)
elem - an object.Object.equals(Object)public int lastIndexOf(Object elem)
elem - the desired element.public Object clone()
public Object[] toArray()
public Object[] toArray(Object[] a)
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 is useful in determining the length of the list only if the caller knows that the list does not contain any null elements.
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.public Object get(int index)
index - index of element to return.
public Object set(int index,
Object element)
index - index of element to replace.element - element to be stored at the specified position.public boolean add(Object o)
o - element to be appended to this list.
public void add(int index,
Object element)
index - index at which the specified element is to be inserted.element - element to be inserted.public Object remove(int index)
index - the index of the element to removed.public void clear()
public boolean addAll(Collection c)
index - index at which to insert first element
from the specified collection.c - elements to be inserted into this list.
public boolean addAll(int index,
Collection c)
index - index at which to insert first element
from the specified collection.c - elements to be inserted into this list.
protected void removeRange(int fromIndex,
int toIndex)
fromIndex - index of first element to be removed.fromIndex - index after last element to be removed.
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Java Platform 1.2 |
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