List Interface in Java

The List interface is a member of the Java Collections Framework.It extends Collection interface.

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.
The List interface provides 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 (the LinkedList class, 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.

The List interface provides a special iterator, called a ListIterator, that allows element insertion and replacement, and bidirectional access in addition to the normal operations that the Iterator interface provides. A method is provided to obtain a list iterator that starts at a specified position in the list.
The List interface provides two 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.
The List interface provides two methods to efficiently insert and remove multiple elements at an arbitrary point in the list.
Note: While it is permissible for lists to contain themselves as elements, extreme caution is advised: the equals and hashCode methods are no longer well defined on a such a list.
Some list implementations have restrictions on the elements that they may contain. For example, some implementations prohibit null elements, and some have restrictions on the types of their elements. Attempting to add an ineligible element throws an unchecked exception, typically NullPointerException or ClassCastException. Attempting to query the presence of an ineligible element may throw an exception, or it may simply return false; some implementations will exhibit the former behavior and some will exhibit the latter. More generally, attempting an operation on an ineligible element whose completion would not result in the insertion of an ineligible element into the list may throw an exception or it may succeed, at the option of the implementation. Such exceptions are marked as "optional" in the specification for this interface.

In addition to the methods inherited from Collection the List interface contains some new methods.Let us discuss about some of them.

Adding and Removing an element

1) public boolean add(Object o)

Appends the specified element to the end of this list (optional operation).

Lists that support this operation may place limitations on what elements may be added to this list. In particular, some lists will refuse to add null elements, and others will impose restrictions on the type of elements that may be added. List classes should clearly specify in their documentation any restrictions on what elements may be added.

Specified by:

add in interface Collection

Parameters:

o - element to be appended to this list.

Returns:

true (as per the general contract of the Collection.add method).

Throws:

UnsupportedOperationException - if the add method is not supported by this list.

ClassCastException - if the class of the specified element prevents it from being added to this list.

NullPointerException - if the specified element is null and this list does not support null elements.

IllegalArgumentException - if some aspect of this element prevents it from being added to this list.

 
2) public void add(int index,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 - if the add method is not supported by this list.

ClassCastException - if the class of the specified element prevents it from being added to this list.

NullPointerException - if the specified element is null and this list does not support null elements.

IllegalArgumentException - if some aspect of the specified element prevents it from being added to this list.

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

3) public boolean remove(Object o)

Removes the first occurrence in this list of the specified element (optional operation). If this 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 this list contained the specified element.

Throws:

ClassCastException - if the type of the specified element is incompatible with this list (optional).

NullPointerException - if the specified element is null and this list does not support null elements (optional).

UnsupportedOperationException - if the remove method is not supported by this list.

4) public 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 - index of element to replace.

element - element to be stored at the specified position.

Returns:

the element previously at the specified position.

Throws:

UnsupportedOperationException - if the set method is not supported by this list.

ClassCastException - if the class of the specified element prevents it from being added to this list.

NullPointerException - if the specified element is null and this list does not support null elements.

IllegalArgumentException - if some aspect of the specified element prevents it from being added to this list.

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

Get and Set an element

1) public Object get(int index)

Returns the element at the specified position in this list.

Parameters:

index - index of element to return.

Returns:

the element at the specified position in this list.

Throws:

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

2) public Object set(int index,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 - if the set method is not supported by this list.

ClassCastException - if the class of the specified element prevents it from being added to this list.

NullPointerException - if the specified element is null and this list does not support null elements.

IllegalArgumentException - if some aspect of the specified element prevents it from being added to this list.

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

Group Operations

1)public 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 (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

Parameters:

c - collection whose elements are to be added to this list.

Returns:

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

Throws:

UnsupportedOperationException - if the addAll method is not supported by this list.

ClassCastException - if the class of an element in the specified collection prevents it from being added to this list.

NullPointerException - if the specified collection contains one or more null elements and this list does not support null elements, or if the specified collection is null.

IllegalArgumentException - if some aspect of an element in the specified collection prevents it from being added to this list.

2) 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 this 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 - if the addAll method is not supported by this list.

ClassCastException - if the class of one of elements of the specified collection prevents it from being added to this list.

NullPointerException - if the specified collection contains one or more null elements and this list does not support null elements, or if the specified collection is null.

IllegalArgumentException - if some aspect of one of elements of the specified collection prevents it from being added to this list.

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

Query Operations

1) public boolean equals(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. This definition ensures that the equals method works properly across different implementations of the List interface.

Specified by:

equals in interface Collection

Overrides:

equals in class Object

Parameters:

o - the object to be compared for equality with this list.

Returns:

true if the specified object is equal to this list.

2) 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 Object

Returns:

the hash code value for this list.

3) public int indexOf(Object o)

Returns the index in this list of the first occurrence of the specified element, or -1 if this 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.

Returns:

the index in this list of the first occurrence of the specified element, or -1 if this list does not contain this element.

Throws:

ClassCastException - if the type of the specified element is incompatible with this list (optional).

NullPointerException - if the specified element is null and this list does not support null elements (optional).

4) public int lastIndexOf(Object o)

Returns the index in this list of the last occurrence of the specified element, or -1 if this 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.

Returns:

the index in this list of the last occurrence of the specified element, or -1 if this list does not contain this element.

Throws:

ClassCastException - if the type of the specified element is incompatible with this list (optional).

NullPointerException - if the specified element is null and this list does not support null elements (optional).

5) public Iterator iterator()

Returns an iterator over the elements in this list in proper sequence.

       Specified by:iterator in interface Collection
      Returns:an iterator over the elements in this list in proper sequence.


6) public ListIterator listIterator()

Returns a list iterator of the elements in this list (in proper sequence).

Returns:

a list iterator of the elements in this list (in proper sequence).

 7) public ListIterator listIterator(int index)

Returns a list iterator of the elements in this list (in proper sequence), starting at the specified position in this list. The specified index indicates the first element that would be returned by an initial call to the next method. An initial call to the previous method would return the element with the specified index minus one.

Parameters:

index - index of first element to be returned from the list iterator (by a call to the next method).

Returns:

a list iterator of the elements in this list (in proper sequence), starting at the specified position in this list.

Throws:

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

8) public List subList(int fromIndex,int toIndex)

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 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, 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.)

Parameters:

fromIndex - low endpoint (inclusive) of the subList.

toIndex - high endpoint (exclusive) of the subList.

Returns:

a view of the specified range within this list.

Throws:

IndexOutOfBoundsException - for an illegal endpoint index value (fromIndex < 0 || toIndex > size || fromIndex > toIndex).



The links you may like:

Collection Interface in Java

ArrayList in Java Collection Framework