Interface java.util.List
- Implementing Classes:
- AbstractList, Collections.SynchronizedList, Collections.UnmodifiableList, LinkedList, Vector, ArrayList
- public abstract interface List
- extends Collection
An ordered Collection (also known as a sequence). The user of this
interface has precise control over where in the List each element is
inserted. The user can access elements by their integer index (position) in
the List, and search for elements in the List.
Unlike Sets, Lists typically allow duplicate elements. More formally,
Lists typically allow pairs of elements e1
and e2
such that e1.equals(e2)
, and they typically allow multiple
null elements if they allow null elements at all. It is not inconceivable
that someone might wish to implement a List that prohibits duplicates,
by throwing runtime exceptions when the user attempts to insert them,
but we expect this usage to be rare.
The List interface places additional stipulations, beyond those specified
in the Collection Interface, on the contracts of the iterator, add,
remove, equals, and hashCode methods. Declarations for other inherited
methods are also included here for convenience.
Lists provide four methods for positional (indexed) access to List
elements. Lists (like Java arrays) are zero based. Note that these
operations may execute in time proportional to the index value for some
implementations (LinkedList, for example). Thus, iterating over the
elements in a List is typically preferable to indexing through it if the
caller does not know the implementation.
List provides a special Iterator, called a ListIterator, that allows
element insertion and replacement, and bidirectional access in addition to
the normal Iterator operations. A method is provided to obtain a List
iterator that starts at a specified position in the List.
List provides four methods to search for a specified object. From a
performance standpoint, these methods should be used with caution.
In many implementations, they will perform costly linear searches.
List provides two methods to efficiently insert and remove multiple
elements at an arbitrary point in the List.
Implemented by ArrayList, LinkedList, Vector, and returned by
Arrays.asList, Collection.subList and Collections.ncopies.
- Since:
- JDK1.2
- Version:
- 1.15 10/13/97
- See Also:
- Collection, Set, ArrayList, LinkedList, Vector, asList(Object[]), Collections#subList(List, int, int), nCopies(int, Object), AbstractList, AbstractSequentialList
Method Summary
|
boolean
|
addAll(Collection c)
Appends all of the elements in the specified Collection to the end of
this this List, in the order that they are returned by the specified
Collection's Iterator (optional operation). |
boolean
|
addAll(int index,
Collection c)
Inserts all of the elements in the specified Collection into this
List at the specified position (optional operation). |
boolean
|
add(java.lang.Object o)
Appends the specified element to the end of this List (optional
operation). |
void
|
add(int index,
java.lang.Object element)
Inserts the specified element at the specified position in this List
(optional operation). |
void
|
clear()
Removes all of the elements from this List (optional operation). |
boolean
|
containsAll(Collection c)
Returns true if this List contains all of the elements of the specified
Collection. |
boolean
|
contains(java.lang.Object o)
Returns true if this List contains the specified element. |
boolean
|
equals(java.lang.Object o)
Compares the specified Object with this List for equality. |
java.lang.Object
|
get(int index)
Returns the element at the specified position in this List. |
int
|
hashCode()
Returns the hash code value for this List. |
int
|
indexOf(java.lang.Object o)
Returns the index in this List of the first occurrence of the specified
element, or -1 if the List does not contain this element.
|
boolean
|
isEmpty()
Returns true if this List contains no elements. |
Iterator
|
iterator()
Returns an Iterator over the elements in this List in proper sequence. |
int
|
lastIndexOf(java.lang.Object o)
Returns the index in this List of the last occurrence of the specified
element, or -1 if the List does not contain this element.
|
ListIterator
|
listIterator()
Returns a ListIterator of the elements in this List (in proper
sequence). |
ListIterator
|
listIterator(int index)
Returns a ListIterator of the elements in this List (in proper
sequence), starting at the specified position in the List. |
boolean
|
removeAll(Collection c)
Removes from this List all of its elements that are contained in the
specified Collection (optional operation). |
boolean
|
remove(java.lang.Object o)
Removes the first occurrence of the specified element in this List
(optional operation). |
java.lang.Object
|
remove(int index)
Removes the element at the specified position in this List (optional
operation). |
boolean
|
retainAll(Collection c)
Retains only the elements in this List that are contained in the
specified Collection (optional operation). |
java.lang.Object
|
set(int index,
java.lang.Object element)
Replaces the element at the specified position in this List with the
specified element (optional operation). |
int
|
size()
Returns the number of elements in this List. |
List
|
subList(int fromIndex,
int toIndex)
Returns a view of the portion of this List between fromIndex,
inclusive, and toIndex, exclusive. |
java.lang.Object[]
|
toArray()
Returns an array containing all of the elements in this List.
|
size
public int size()
- Returns the number of elements in this List.
- Specified by:
- size in interface Collection
isEmpty
public boolean isEmpty()
- Returns true if this List contains no elements.
- Specified by:
- isEmpty in interface Collection
contains
public boolean contains(java.lang.Object o)
- 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
- Parameters:
o
- element whose presence in this List is to be tested.
iterator
public Iterator iterator()
- Returns an Iterator over the elements in this List in proper sequence.
- Specified by:
- iterator in interface Collection
toArray
public java.lang.Object[] toArray()
- Returns an array containing all of the elements in this List.
Obeys the general contract of Collection.toArray.
- Specified by:
- toArray in interface Collection
- See Also:
- asList(Object[])
add
public boolean add(java.lang.Object o)
- Appends the specified element to the end of this List (optional
operation).
- Specified by:
- add in interface Collection
- Parameters:
o
- element to be appended to this List.- Returns:
- true (as per the general contract of Collection.add).
- Throws:
- UnsupportedOperationException - add is not supported
by this Set.
- ClassCastException - class of the specified element
prevents it from being added to this Set.
- java.lang.IllegalArgumentException - some aspect of this element prevents
it from being added to this Collection.
remove
public boolean remove(java.lang.Object o)
- Removes the first occurrence of the specified element in this List
(optional operation). If the List does not contain the element, it is
unchanged. More formally, removes the element with the lowest index i
such that
(o==null ? get(i)==null : o.equals(get(i)))
(if
such an element exists).
- Specified by:
- remove in interface Collection
- Parameters:
o
- element to be removed from this List, if present.- Returns:
- true if the List contained the specified element.
- Throws:
- UnsupportedOperationException - remove is not supported
by this List.
containsAll
public boolean containsAll(Collection c)
- Returns true if this List contains all of the elements of the specified
Collection.
- Specified by:
- containsAll in interface Collection
- See Also:
- contains(Object)
addAll
public boolean addAll(Collection c)
- Appends all of the elements in the specified Collection to the end of
this this List, in the order that they are returned by the specified
Collection's Iterator (optional operation). The behavior of this
operation is unspecified if the specified Collection is modified while
the operation is in progress. (Note that this will occur if the
specified Collection is this List, and it's nonempty.)
- Specified by:
- addAll in interface Collection
- Returns:
- true if this List changed as a result of the call.
- Throws:
- UnsupportedOperationException - addAll is not supported
by this List.
- ClassCastException - class of an element in the specified
Collection prevents it from being added to this List.
- java.lang.IllegalArgumentException - some aspect of an element in the
specified Collection prevents it from being added to this
List.
- See Also:
- add(Object)
addAll
public boolean addAll(int index,
Collection c)
- Inserts all of the elements in the specified Collection into this
List at the specified position (optional operation). 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. The behavior of this operation is
unspecified if the specified Collection is modified while the
operation is in progress. (Note that this will occur if the specified
Collection is this List, and it's nonempty.)
- Parameters:
index
- index at which to insert first element from the specified
Collection.
c
- elements to be inserted into this List.- Returns:
- true if this List changed as a result of the call.
- Throws:
- UnsupportedOperationException - addAll is not supported
by this List.
- ClassCastException - class of one of elements of the specified
Collection prevents it from being added to this List.
- java.lang.IllegalArgumentException - some aspect of one of elements of
the specified Collection prevents it from being added to
this List.
- IndexOutOfBoundsException - index out of range (index
< 0 || index > size()).
removeAll
public boolean removeAll(Collection c)
- Removes from this List all of its elements that are contained in the
specified Collection (optional operation).
- Specified by:
- removeAll in interface Collection
- Returns:
- true if this List changed as a result of the call.
- Throws:
- UnsupportedOperationException - removeAll is not supported
by this List.
- See Also:
- remove(Object), contains(Object)
retainAll
public boolean retainAll(Collection c)
- Retains only the elements in this List that are contained in the
specified Collection (optional operation). In other words, removes from
this List all of its elements that are not contained in the specified
Collection.
- Specified by:
- retainAll in interface Collection
- Returns:
- true if this List changed as a result of the call.
- Throws:
- UnsupportedOperationException - retainAll is not supported
by this List.
- See Also:
- remove(Object), contains(Object)
clear
public void clear()
- Removes all of the elements from this List (optional operation). The
List will be empty after this call returns (unless it throws an
exception).
- Specified by:
- clear in interface Collection
- Throws:
- UnsupportedOperationException - clear is not supported
by this List.
equals
public boolean equals(java.lang.Object o)
- 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.
- Specified by:
- equals in interface Collection
- Parameters:
o
- the Object to be compared for equality with this List.- Returns:
- true if the specified Object is equal to this List.
- Overrides:
- equals in class java.lang.Object
hashCode
public int hashCode()
- Returns the hash code value for this List. The hash code of a List
is defined to be the result of the following calculation:
hashCode = 1;
Iterator i = list.iterator();
while (i.hasNext()) {
Object obj = i.next();
hashCode = 31*hashCode + (obj==null ? 0 : obj.hashCode());
}
This ensures that list1.equals(list2)
implies that
list1.hashCode()==list2.hashCode()
for any two Lists,
list1
and list2
, as required by the general
contract of Object.hashCode.
- Specified by:
- hashCode in interface Collection
- Overrides:
- hashCode in class java.lang.Object
- See Also:
- hashCode(), equals(Object), equals(Object)
get
public java.lang.Object get(int index)
- Returns the element at the specified position in this List.
- Parameters:
index
- index of element to return.- Throws:
- IndexOutOfBoundsException - index is out of range (index
< 0 || index >= size()).
set
public java.lang.Object set(int index,
java.lang.Object element)
- Replaces the element at the specified position in this List with the
specified element (optional operation).
- Parameters:
index
- index of element to replace.
element
- element to be stored at the specified position.- Returns:
- the element previously at the specified position.
- Throws:
- UnsupportedOperationException - set is not supported
by this List.
- ClassCastException - class of the specified element
prevents it from being added to this List.
- java.lang.IllegalArgumentException - some aspect of the specified
element prevents it from being added to this List.
- IndexOutOfBoundsException - index out of range
(index < 0 || index >= size()).
add
public void add(int index,
java.lang.Object element)
- Inserts the specified element at the specified position in this List
(optional operation). Shifts the element currently at that position
(if any) and any subsequent elements to the right (adds one to their
indices).
- Parameters:
index
- index at which the specified element is to be inserted.
element
- element to be inserted.- Throws:
- UnsupportedOperationException - add is not supported
by this List.
- ClassCastException - class of the specified element
prevents it from being added to this List.
- java.lang.IllegalArgumentException - some aspect of the specified
element prevents it from being added to this List.
- IndexOutOfBoundsException - index is out of range
(index < 0 || index > size()).
remove
public java.lang.Object remove(int index)
- Removes the element at the specified position in this List (optional
operation). Shifts any subsequent elements to the left (subtracts one
from their indices). Returns the element that was removed from the
List.
- Parameters:
index
- the index of the element to removed.- Returns:
- the element previously at the specified position.
- Throws:
- UnsupportedOperationException - remove is not supported
by this List.
- IndexOutOfBoundsException - index out of range (index
< 0 || index >= size()).
indexOf
public int indexOf(java.lang.Object o)
- Returns the index in this List of the first occurrence of the specified
element, or -1 if the List does not contain this element.
More formally, returns the lowest index i such that
(o==null ? get(i)==null : o.equals(get(i)))
,
or -1 if there is no such index.
- Parameters:
o
- element to search for.
lastIndexOf
public int lastIndexOf(java.lang.Object o)
- Returns the index in this List of the last occurrence of the specified
element, or -1 if the List does not contain this 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.
- Parameters:
o
- element to search for.
listIterator
public ListIterator listIterator()
- Returns a ListIterator of the elements in this List (in proper
sequence).
listIterator
public ListIterator listIterator(int index)
- Returns a ListIterator of 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 nextElement. An initial call to previousElement
would return the element with the specified index minus one.
- Parameters:
index
- index of first element to be returned from the
ListIterator (by a call to getNext).- Throws:
- IndexOutOfBoundsException - index is out of range
(index < 0 || index > size()).
subList
public List subList(int fromIndex,
int toIndex)
- Returns a view of the portion of this List between fromIndex,
inclusive, and toIndex, exclusive. The returned List is backed by this
List, so changes in the returned List are reflected in this List, and
vice-versa. The returned List supports all of the optional List
operations supported by this List.
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 and lastIndexOf.
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 the List, or otherwise perturb it in such
a fashion that iterations in progress may yield incorrect results.)
- Parameters:
fromIndex
- low endpoint (inclusive) of the subList.
toKey
- high endpoint (exclusive) of the subList.- Returns:
- a view of the specified range within this List.
- Throws:
- IndexOutOfBoundsException - Illegal endpoint index value
(fromIndex < 0 || toIndex > size || fromIndex > toIndex).