E - the type of elements in this list
Serializable, Cloneable, Iterable<E>, Collection<E>, List<E>, RandomAccess
AttributeList, RoleList, RoleUnresolvedList
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 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. 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.
Constructors
Constructs an empty list with an initial capacity of ten.
Constructs an empty list with the specified initial capacity.
Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.
void
add(int index, E element)
Inserts the specified element at the specified position in this list.
boolean
Appends the specified element to the end of this list.
boolean
Inserts all of the elements in the specified collection into this list, starting at the specified position.
boolean
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.
void
Removes all of the elements from this list.
Returns a shallow copy of this ArrayList instance.
boolean
Returns true if this list contains the specified element.
void
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.
boolean
Compares the specified object with this list for equality.
void
Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception.
Returns the element at the specified position in this list.
int
Returns the hash code value for this list.
int
Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.
boolean
Returns true if this list contains no elements.
Returns an iterator over the elements in this list in proper sequence.
int
Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element.
Returns a list iterator over the elements in this list (in proper sequence).
Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list.
Removes the element at the specified position in this list.
boolean
Removes the first occurrence of the specified element from this list, if it is present.
boolean
Removes from this list all of its elements that are contained in the specified collection.
boolean
Removes all of the elements of this collection that satisfy the given predicate.
protected void
Removes from this list all of the elements whose index is between fromIndex, inclusive, and toIndex, exclusive.
boolean
Retains only the elements in this list that are contained in the specified collection.
set(int index, E element)
Replaces the element at the specified position in this list with the specified element.
int
Returns the number of elements in this list.
subList(int fromIndex, int toIndex)
Returns a view of the portion of this list between the specified fromIndex, inclusive, and toIndex, exclusive.
Returns an array containing all of the elements in this list in proper sequence (from first to last element).
<T> T[]
Returns an array containing all of the elements in this list in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array.
void
Trims the capacity of this ArrayList instance to be the list's current size.
public ArrayList(int initialCapacity)
Constructs an empty list with the specified initial capacity.
initialCapacity - the initial capacity of the list
IllegalArgumentException - if the specified initial capacity is negative
public ArrayList()
Constructs an empty list with an initial capacity of ten.
Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.
c - the collection whose elements are to be placed into this list
NullPointerException - if the specified collection is null
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.
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.
minCapacity - the desired minimum capacity
public int size()
Returns the number of elements in this list.
public boolean isEmpty()
Returns true if this list contains no elements.
isEmpty in interface Collection<E>
isEmpty in interface List<E>
isEmpty in class AbstractCollection<E>
true if this list contains no elements
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 Objects.equals(o, e).
contains in interface Collection<E>
contains in interface List<E>
contains in class AbstractCollection<E>
o - element whose presence in this list is to be tested
true if this list contains the specified element
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 i such that Objects.equals(o, get(i)), or -1 if there is no such index.
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 Objects.equals(o, get(i)), or -1 if there is no such index.
lastIndexOf in interface List<E>
lastIndexOf in class AbstractList<E>
o - element to search for
Returns a shallow copy of this ArrayList instance. (The elements themselves are not copied.)
Returns an array containing all of the elements in this list in proper sequence (from first to last element).
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.
toArray in interface Collection<E>
toArray in interface List<E>
toArray in class AbstractCollection<E>
public <T> T[] toArray(T[] 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.)
toArray in interface Collection<E>
toArray in interface List<E>
toArray in class AbstractCollection<E>
T - the component type of the array to contain the collection
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.
ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this list
NullPointerException - if the specified array is null
Returns the element at the specified position in this list.
get in interface List<E>
get in class AbstractList<E>
index - index of the element to return
IndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())
Replaces the element at the specified position in this list with the specified element.
set in interface List<E>
set in class AbstractList<E>
index - index of the element to replace
element - element to be stored at the specified position
IndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())
Appends the specified element to the end of this list.
add in interface Collection<E>
add in interface List<E>
add in class AbstractList<E>
e - element to be appended to this list
true (as specified by Collection.add(E))
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).
add in interface List<E>
add in class AbstractList<E>
index - index at which the specified element is to be inserted
element - element to be inserted
IndexOutOfBoundsException - if the index is out of range (index < 0 || index > size())
Removes the element at the specified position in this list. Shifts any subsequent elements to the left (subtracts one from their indices).
remove in interface List<E>
remove in class AbstractList<E>
index - the index of the element to be removed
IndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())
Compares the specified object with this list for equality. Returns true if and only if the specified object is also a list, both lists have the same size, and all corresponding pairs of elements in the two lists are equal. (Two elements e1 and e2 are equal if (e1==null ? e2==null : e1.equals(e2)).) In other words, two lists are defined to be equal if they contain the same elements in the same order.
equals in interface Collection<E>
equals in interface List<E>
equals in class AbstractList<E>
o - the object to be compared for equality with this list
true if the specified object is equal to this list
public int hashCode()
Returns the hash code value for this list.
hashCode in interface Collection<E>
hashCode in interface List<E>
hashCode in class AbstractList<E>
Removes the first occurrence of the specified element from this list, if it is present. If the list does not contain the element, it is unchanged. More formally, removes the element with the lowest index i such that Objects.equals(o, get(i)) (if such an element exists). Returns true if this list contained the specified element (or equivalently, if this list changed as a result of the call).
remove in interface Collection<E>
remove in interface List<E>
remove in class AbstractCollection<E>
o - element to be removed from this list, if present
true if this list contained the specified element
public void clear()
Removes all of the elements from this list. The list will be empty after this call returns.
clear in interface Collection<E>
clear in interface List<E>
clear in class AbstractList<E>
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. 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 list, and this list is nonempty.)
addAll in interface Collection<E>
addAll in interface List<E>
addAll in class AbstractCollection<E>
c - collection containing elements to be added to this list
true if this list changed as a result of the call
NullPointerException - if the specified collection is null
Inserts all of the elements in the specified 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 iterator.
addAll in interface List<E>
addAll in class AbstractList<E>
index - index at which to insert the first element from the specified collection
c - collection containing elements to be added to this list
true if this list changed as a result of the call
IndexOutOfBoundsException - if the index is out of range (index < 0 || index > size())
NullPointerException - if the specified collection is null
protected void removeRange(int fromIndex, int toIndex)
Removes from this list all of the elements whose index is between fromIndex, inclusive, and 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.)
removeRange in class AbstractList<E>
fromIndex - index of first element to be removed
toIndex - index after last element to be removed
IndexOutOfBoundsException - if fromIndex or toIndex is out of range (fromIndex < 0 || toIndex > size() || toIndex < fromIndex)
Removes from this list all of its elements that are contained in the specified collection.
removeAll in interface Collection<E>
removeAll in interface List<E>
removeAll in class AbstractCollection<E>
c - collection containing elements to be removed from this list
true if this list changed as a result of the call
ClassCastException - if the class of an element of this list is incompatible with the specified collection (optional)
NullPointerException - if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null
Retains only the elements in this list that are contained in the specified collection. In other words, removes from this list all of its elements that are not contained in the specified collection.
retainAll in interface Collection<E>
retainAll in interface List<E>
retainAll in class AbstractCollection<E>
c - collection containing elements to be retained in this list
true if this list changed as a result of the call
ClassCastException - if the class of an element of this list is incompatible with the specified collection (optional)
NullPointerException - if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null
Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list. The specified index indicates the first element that would be returned by an initial call to
next
. An initial call to
previous
would return the element with the specified index minus one.
The returned list iterator is fail-fast.
listIterator in interface List<E>
listIterator in class AbstractList<E>
index - index of the first element to be returned from the list iterator (by a call to next)
IndexOutOfBoundsException - if the index is out of range (index < 0 || index > size())
The returned list iterator is fail-fast.
listIterator in interface List<E>
listIterator in class AbstractList<E>
The returned iterator is fail-fast.
Returns a view of the portion of this list between the specified
fromIndex
, inclusive, and
toIndex
, exclusive. (If
fromIndex
and
toIndex
are equal, the returned list is empty.) The returned list is backed by this list, so non-structural changes in the returned list are reflected in this list, and vice-versa. The returned list supports all of the optional list operations.
This method eliminates the need for explicit range operations (of the sort that commonly exist for arrays). Any operation that expects a list can be used as a range operation by passing a subList view instead of a whole list. For example, the following idiom removes a range of elements from a list:
list.subList(from, to).clear();
Similar idioms may be constructed for
indexOf(Object)
and
lastIndexOf(Object)
, and all of the algorithms in the
Collections
class can be applied to a subList.
The semantics of the list returned by this method become undefined if the backing list (i.e., this list) is structurally modified in any way other than via the returned list. (Structural modifications are those that change the size of this list, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results.)
subList in interface List<E>
subList in class AbstractList<E>
fromIndex - low endpoint (inclusive) of the subList
toIndex - high endpoint (exclusive) of the subList
IndexOutOfBoundsException - if an endpoint index value is out of range (fromIndex < 0 || toIndex > size)
IllegalArgumentException - if the endpoint indices are out of order (fromIndex > toIndex)
Iterable
Performs the given action for each element of the
Iterable
until all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller.
The behavior of this method is unspecified if the action performs side-effects that modify the underlying source of elements, unless an overriding class has specified a concurrent modification policy.
forEach in interface Iterable<E>
action - The action to be performed for each element
NullPointerException - if the specified action is null
spliterator in interface Collection<E>
spliterator in interface Iterable<E>
spliterator in interface List<E>
Spliterator over the elements in this list
Removes all of the elements of this collection that satisfy the given predicate. Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.
removeIf in interface Collection<E>
filter - a predicate which returns true for elements to be removed
true if any elements were removed
NullPointerException - if the specified filter is null
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