List

All Superinterfaces:

Collection

All Known Implementing Classes:

AbstractList, ArrayList
```
public interface List
extends Collection
```
An ordered collection (also known as a list). This collection allows access to elements by position, as well as control on where elements are inserted. Unlike sets, duplicate elements are permitted by this general contract (if a subclass forbids duplicates, this should be documented).
List places additional requirements on iterator, add, remove, equals, and hashCode, in addition to requiring more methods. List indexing is 0-based (like arrays), although some implementations may require time proportional to the index to obtain an arbitrary element. The List interface is incompatible with Set; you cannot implement both simultaneously.
Lists also provide a ListIterator which allows bidirectional traversal and other features atop regular iterators. Lists can be searched for arbitrary elements, and allow easy insertion and removal of multiple elements in one method call.
Note: While lists may contain themselves as elements, this leads to undefined (usually infinite recursive) behavior for some methods like hashCode or equals.

Author:

Original author unknown, Eric Blake

See Also:

Collection, Set, ArrayList, LinkedList, Vector

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method and Description
`void`	`add(int index, Object o)` Insert an element into the list at a given position (optional operation).
`boolean`	`add(Object o)` Add an element to the end of the list (optional operation).
`boolean`	`addAll(Collection c)` Add the contents of a collection to the end of the list (optional operation).
`boolean`	`addAll(int index, Collection c)` Insert the contents of a collection into the list at a given position (optional operation).
`void`	`clear()` Clear the list, such that a subsequent call to isEmpty() would return true (optional operation).
`boolean`	`contains(Object o)` Test whether this list contains a given object as one of its elements.
`boolean`	`containsAll(Collection c)` Test whether this list contains every element in a given collection.
`boolean`	`equals(Object o)` Test whether this list is equal to another object.
`Object`	`get(int index)` Get the element at a given index in this list.
`int`	`hashCode()` Obtains a hash code for this list.
`int`	`indexOf(Object o)` Obtain the first index at which a given object is to be found in this list.
`boolean`	`isEmpty()` Test whether this list is empty, that is, if size() == 0.
`Iterator`	`iterator()` Obtain an Iterator over this list, whose sequence is the list order.
`int`	`lastIndexOf(Object o)` Obtain the last index at which a given object is to be found in this list.
`ListIterator`	`listIterator()` Obtain a ListIterator over this list, starting at the beginning.
`ListIterator`	`listIterator(int index)` Obtain a ListIterator over this list, starting at a given position.
`Object`	`remove(int index)` Remove the element at a given position in this list (optional operation).
`boolean`	`remove(Object o)` Remove the first occurence of an object from this list (optional operation).
`boolean`	`removeAll(Collection c)` Remove all elements of a given collection from this list (optional operation).
`boolean`	`retainAll(Collection c)` Remove all elements of this list that are not contained in a given collection (optional operation).
`Object`	`set(int index, Object o)` Replace an element of this list with another object (optional operation).
`int`	`size()` Get the number of elements in this list.
`List`	`subList(int fromIndex, int toIndex)` Obtain a List view of a subsection of this list, from fromIndex (inclusive) to toIndex (exclusive).
`Object[]`	`toArray()` Copy the current contents of this list into an array.
`Object[]`	`toArray(Object[] a)` Copy the current contents of this list into an array.

- Method Detail
  - add
```
void add(int index,
         Object o)
```
    Insert an element into the list at a given position (optional operation). This shifts all existing elements from that position to the end one index to the right. This version of add has no return, since it is assumed to always succeed if there is no exception.
    
    Parameters:
    
    index - the location to insert the item
    
    o - the object to insert
    
    Throws:
    
    UnsupportedOperationException - if this list does not support the add operation
    
    IndexOutOfBoundsException - if index < 0 || index > size()
    
    ClassCastException - if o cannot be added to this list due to its type
    
    IllegalArgumentException - if o cannot be added to this list for some other reason
  - add
```
boolean add(Object o)
```
    Add an element to the end of the list (optional operation). If the list imposes restraints on what can be inserted, such as no null elements, this should be documented.
    
    Specified by:
    
    add in interface Collection
    
    Parameters:
    
    o - the object to add
    
    Returns:
    
    true, as defined by Collection for a modified list
    
    Throws:
    
    UnsupportedOperationException - if this list does not support the add operation
    
    ClassCastException - if o cannot be added to this list due to its type
    
    IllegalArgumentException - if o cannot be added to this list for some other reason
  - addAll
```
boolean addAll(int index,
               Collection c)
```
    Insert the contents of a collection into the list at a given position (optional operation). Shift all elements at that position to the right by the number of elements inserted. This operation is undefined if this list is modified during the operation (for example, if you try to insert a list into itself).
    
    Parameters:
    
    index - the location to insert the collection
    
    c - the collection to insert
    
    Returns:
    
    true if the list was modified by this action, that is, if c is non-empty
    
    Throws:
    
    UnsupportedOperationException - if this list does not support the addAll operation
    
    IndexOutOfBoundsException - if index < 0 || index > size()
    
    ClassCastException - if some element of c cannot be added to this list due to its type
    
    IllegalArgumentException - if some element of c cannot be added to this list for some other reason
    
    NullPointerException - if the specified collection is null
    
    See Also:
    
    add(int, Object)
  - addAll
```
boolean addAll(Collection c)
```
    Add the contents of a collection to the end of the list (optional operation). This operation is undefined if this list is modified during the operation (for example, if you try to insert a list into itself).
    
    Specified by:
    
    addAll in interface Collection
    
    Parameters:
    
    c - the collection to add
    
    Returns:
    
    true if the list was modified by this action, that is, if c is non-empty
    
    Throws:
    
    UnsupportedOperationException - if this list does not support the addAll operation
    
    ClassCastException - if some element of c cannot be added to this list due to its type
    
    IllegalArgumentException - if some element of c cannot be added to this list for some other reason
    
    NullPointerException - if the specified collection is null
    
    See Also:
    
    add(Object)
  - clear
```
void clear()
```
    Clear the list, such that a subsequent call to isEmpty() would return true (optional operation).
    
    Specified by:
    
    clear in interface Collection
    
    Throws:
    
    UnsupportedOperationException - if this list does not support the clear operation
  - contains
```
boolean contains(Object o)
```
    Test whether this list contains a given object as one of its elements. This is defined as the existence of an element e such that o == null ? e == null : o.equals(e).
    
    Specified by:
    
    contains in interface Collection
    
    Parameters:
    
    o - the element to look for
    
    Returns:
    
    true if this list contains the element
  - containsAll
```
boolean containsAll(Collection c)
```
    Test whether this list contains every element in a given collection.
    
    Specified by:
    
    containsAll in interface Collection
    
    Parameters:
    
    c - the collection to test for
    
    Returns:
    
    true if for every element o in c, contains(o) would return true
    
    Throws:
    
    NullPointerException - if the collection is null
    
    See Also:
    
    contains(Object)
  - equals
```
boolean equals(Object o)
```
    Test whether this list is equal to another object. A List is defined to be equal to an object if and only if that object is also a List, and the two lists have the same sequence. Two lists l1 and l2 are equal if and only if l1.size() == l2.size(), and for every integer n between 0 and l1.size() - 1 inclusive, l1.get(n) == null ? l2.get(n) == null : l1.get(n).equals(l2.get(n)).
    
    Specified by:
    
    equals in interface Collection
    
    Overrides:
    
    equals in class Object
    
    Parameters:
    
    o - the object to test for equality with this list
    
    Returns:
    
    true if o is equal to this list
    
    See Also:
    
    Object.equals(Object), hashCode()
  - get
```
Object get(int index)
```
    Get the element at a given index in this list.
    
    Parameters:
    
    index - the index of the element to be returned
    
    Returns:
    
    the element at index index in this list
    
    Throws:
    
    IndexOutOfBoundsException - if index < 0 || index >= size()
  - hashCode
```
int hashCode()
```
    Obtains a hash code for this list. In order to obey the general contract of the hashCode method of class Object, this value is calculated as follows:
```
hashCode = 1;
Iterator i = list.iterator();
while (i.hasNext())
{
  Object obj = i.next();
  hashCode = 31 * hashCode + (obj == null ? 0 : obj.hashCode());
}
```
    This ensures that the general contract of Object.hashCode() is adhered to.
    Specified by:
    
    hashCode in interface Collection
    
    Overrides:
    
    hashCode in class Object
    
    Returns:
    
    the hash code of this list
    
    See Also:
    
    Object.hashCode(), equals(Object)
  - indexOf
```
int indexOf(Object o)
```
    Obtain the first index at which a given object is to be found in this list.
    
    Parameters:
    
    o - the object to search for
    
    Returns:
    
    the least integer n such that o == null ? get(n) == null : o.equals(get(n)), or -1 if there is no such index
  - isEmpty
```
boolean isEmpty()
```
    Test whether this list is empty, that is, if size() == 0.
    
    Specified by:
    
    isEmpty in interface Collection
    
    Returns:
    
    true if this list contains no elements
  - iterator
```
Iterator iterator()
```
    Obtain an Iterator over this list, whose sequence is the list order.
    
    Specified by:
    
    iterator in interface Collection
    
    Returns:
    
    an Iterator over the elements of this list, in order
  - lastIndexOf
```
int lastIndexOf(Object o)
```
    Obtain the last index at which a given object is to be found in this list.
    
    Returns:
    
    the greatest integer n such that o == null ? get(n) == null : o.equals(get(n)), or -1 if there is no such index
  - listIterator
```
ListIterator listIterator()
```
    Obtain a ListIterator over this list, starting at the beginning.
    
    Returns:
    
    a ListIterator over the elements of this list, in order, starting at the beginning
  - listIterator
```
ListIterator listIterator(int index)
```
    Obtain a ListIterator over this list, starting at a given position. A first call to next() would return the same as get(index), and a first call to previous() would return the same as get(index - 1).
    
    Parameters:
    
    index - the position, between 0 and size() inclusive, to begin the iteration from
    
    Returns:
    
    a ListIterator over the elements of this list, in order, starting at index
    
    Throws:
    
    IndexOutOfBoundsException - if index < 0 || index > size()
  - remove
```
Object remove(int index)
```
    Remove the element at a given position in this list (optional operation). Shifts all remaining elements to the left to fill the gap.
    
    Parameters:
    
    index - the position within the list of the object to remove
    
    Returns:
    
    the object that was removed
    
    Throws:
    
    UnsupportedOperationException - if this list does not support the remove operation
    
    IndexOutOfBoundsException - if index < 0 || index >= size()
  - remove
```
boolean remove(Object o)
```
    Remove the first occurence of an object from this list (optional operation). That is, remove the first element e such that o == null ? e == null : o.equals(e).
    
    Specified by:
    
    remove in interface Collection
    
    Parameters:
    
    o - the object to remove
    
    Returns:
    
    true if the list changed as a result of this call, that is, if the list contained at least one occurrence of o
    
    Throws:
    
    UnsupportedOperationException - if this list does not support the remove operation
  - removeAll
```
boolean removeAll(Collection c)
```
    Remove all elements of a given collection from this list (optional operation). That is, remove every element e such that c.contains(e).
    
    Specified by:
    
    removeAll in interface Collection
    
    Parameters:
    
    c - the collection to filter out
    
    Returns:
    
    true if this list was modified as a result of this call
    
    Throws:
    
    UnsupportedOperationException - if this list does not support the removeAll operation
    
    NullPointerException - if the collection is null
    
    See Also:
    
    remove(Object), contains(Object)
  - retainAll
```
boolean retainAll(Collection c)
```
    Remove all elements of this list that are not contained in a given collection (optional operation). That is, remove every element e such that !c.contains(e).
    
    Specified by:
    
    retainAll in interface Collection
    
    Parameters:
    
    c - the collection to retain
    
    Returns:
    
    true if this list was modified as a result of this call
    
    Throws:
    
    UnsupportedOperationException - if this list does not support the retainAll operation
    
    NullPointerException - if the collection is null
    
    See Also:
    
    remove(Object), contains(Object)
  - set
```
Object set(int index,
           Object o)
```
    Replace an element of this list with another object (optional operation).
    
    Parameters:
    
    index - the position within this list of the element to be replaced
    
    o - the object to replace it with
    
    Returns:
    
    the object that was replaced
    
    Throws:
    
    UnsupportedOperationException - if this list does not support the set operation
    
    IndexOutOfBoundsException - if index < 0 || index >= size()
    
    ClassCastException - if o cannot be added to this list due to its type
    
    IllegalArgumentException - if o cannot be added to this list for some other reason
  - size
```
int size()
```
    Get the number of elements in this list. If the list contains more than Integer.MAX_VALUE elements, return Integer.MAX_VALUE.
    
    Specified by:
    
    size in interface Collection
    
    Returns:
    
    the number of elements in the list
  - subList
```
List subList(int fromIndex,
             int toIndex)
```
    Obtain a List view of a subsection of this list, from fromIndex (inclusive) to toIndex (exclusive). If the two indices are equal, the sublist is empty. The returned list should be modifiable if and only if this list is modifiable. Changes to the returned list should be reflected in this list. If this list is structurally modified in any way other than through the returned list, the result of any subsequent operations on the returned list is undefined.
    
    Parameters:
    
    fromIndex - the index that the returned list should start from (inclusive)
    
    toIndex - the index that the returned list should go to (exclusive)
    
    Returns:
    
    a List backed by a subsection of this list
    
    Throws:
    
    IndexOutOfBoundsException - if fromIndex < 0 || toIndex > size() || fromIndex > toIndex
    
    IllegalArgumentException - if fromIndex > toIndex (according to AbstractList). Don't you love Sun's inconsistent specifications?
  - toArray
```
Object[] toArray()
```
    Copy the current contents of this list into an array.
    
    Specified by:
    
    toArray in interface Collection
    
    Returns:
    
    an array of type Object[] and length equal to the length of this list, containing the elements currently in this list, in order
  - toArray
```
Object[] toArray(Object[] a)
```
    Copy the current contents of this list into an array. If the array passed as an argument has length less than that of this list, an array of the same run-time type as a, and length equal to the length of this list, is allocated using Reflection. Otherwise, a itself is used. The elements of this list are copied into it, and if there is space in the array, the following element is set to null. The resultant array is returned. Note: The fact that the following element is set to null is only useful if it is known that this list does not contain any null elements.
    
    Specified by:
    
    toArray in interface Collection
    
    Parameters:
    
    a - the array to copy this list into
    
    Returns:
    
    an array containing the elements currently in this list, in order
    
    Throws:
    
    ArrayStoreException - if the type of any element of the collection is not a subtype of the element type of a
    
    NullPointerException - if the specified array is null

Interface List

Method Summary

Method Detail

add

add

addAll

addAll

clear

contains

containsAll

equals

get

hashCode

indexOf

isEmpty

iterator

lastIndexOf

listIterator

listIterator

remove

remove

removeAll

retainAll

set

size

subList

toArray

toArray