java.util
Class Collections.UnmodifiableList

java.lang.Object
  java.util.Collections.UnmodifiableCollection
      java.util.Collections.UnmodifiableList

All Implemented Interfaces:

Collection, List, Serializable

Direct Known Subclasses:

Collections.UnmodifiableRandomAccessList

Enclosing class:

Collections

static class Collections.UnmodifiableList

extends Collections.UnmodifiableCollection

implements List

See Also:

Serialized Form

Field Summary

(package private) Collection	c
(package private) List	list
(package private) static long	serialVersionUID

Constructor Summary

(package private)

Collections.UnmodifiableList(List list)

Method Summary

void	add(int index, Object element) Inserts the specified element at the specified position in this list (optional operation).
boolean	add(Object o) Appends the specified element to the end of this list (optional operation).
boolean	addAll(Collection coll) 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).
boolean	addAll(int index, Collection c) Inserts all of the elements in the specified collection into this list at the specified position (optional operation).
void	clear() Removes all of the elements from this list (optional operation).
boolean	contains(Object o) Returns true if this list contains the specified element.
boolean	containsAll(Collection coll) Returns true if this list contains all of the elements of the specified collection.
boolean	equals(Object o) Compares the specified object with this list for equality.
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(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.
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(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.
ListIterator	listIterator() Returns a list iterator of the elements in this list (in proper sequence).
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.
private Object	readResolve() UnmodifiableRandomAccessList instances are serialized as UnmodifiableList instances to allow them to be deserialized in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList).
Object	remove(int index) Removes the element at the specified position in this list (optional operation).
boolean	remove(Object o) Removes the first occurrence in this list of the specified element (optional operation).
boolean	removeAll(Collection coll) Removes from this list all the elements that are contained in the specified collection (optional operation).
boolean	retainAll(Collection coll) Retains only the elements in this list that are contained in the specified collection (optional operation).
Object	set(int index, 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 the specified fromIndex, inclusive, and toIndex, exclusive.
Object[]	toArray() Returns an array containing all of the elements in this list in proper sequence.
Object[]	toArray(Object[] a) Returns an array containing all of the elements in this list in proper sequence; the runtime type of the returned array is that of the specified array.
String	toString() Returns a string representation of the object.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.List

add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray

Field Detail

serialVersionUID

static final long serialVersionUID

See Also:

Constant Field Values

list

List list

c

Collection c

Constructor Detail

Collections.UnmodifiableList

Collections.UnmodifiableList(List list)

Method Detail

equals

public boolean equals(Object o)

Description copied from interface: List

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 List

Overrides:

equals in class Object

Parameters:

o - the reference object with which to compare.

Returns:

true if this object is the same as the obj argument; false otherwise.

See Also:

Object.hashCode(), Hashtable

hashCode

public int hashCode()

Description copied from interface: List

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 List

Overrides:

hashCode in class Object

Returns:

a hash code value for this object.

See Also:

Object.equals(java.lang.Object), Hashtable

get

public Object get(int index)

Description copied from interface: List

Returns the element at the specified position in this list.

Specified by:

get in interface List

Parameters:

index - index of element to return.

Returns:

the element at the specified position in this list.

set

public Object set(int index,
                  Object element)

Description copied from interface: List

Replaces the element at the specified position in this list with the specified element (optional operation).

Specified by:

set in interface 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.

add

public void add(int index,
                Object element)

Description copied from interface: List

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).

Specified by:

add in interface List

Parameters:

index - index at which the specified element is to be inserted.

element - element to be inserted.

remove

public Object remove(int index)

Description copied from interface: List

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.

Specified by:

remove in interface List

Parameters:

index - the index of the element to removed.

Returns:

the element previously at the specified position.

indexOf

public int indexOf(Object o)

Description copied from interface: List

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.

Specified by:

indexOf in interface List

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.

lastIndexOf

public int lastIndexOf(Object o)

Description copied from interface: List

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.

Specified by:

lastIndexOf in interface List

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.

addAll

public boolean addAll(int index,
                      Collection c)

Description copied from interface: List

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.)

Specified by:

addAll in interface List

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.

listIterator

public ListIterator listIterator()

Description copied from interface: List

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

Specified by:

listIterator in interface List

Returns:

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

listIterator

public ListIterator listIterator(int index)

Description copied from interface: List

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.

Specified by:

listIterator in interface List

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.

subList

public List subList(int fromIndex,
                    int toIndex)

Description copied from interface: List

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.)

Specified by:

subList in interface List

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.

readResolve

private Object readResolve()

UnmodifiableRandomAccessList instances are serialized as UnmodifiableList instances to allow them to be deserialized in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList). This method inverts the transformation. As a beneficial side-effect, it also grafts the RandomAccess marker onto UnmodifiableList instances that were serialized in pre-1.4 JREs. Note: Unfortunately, UnmodifiableRandomAccessList instances serialized in 1.4.1 and deserialized in 1.4 will become UnmodifiableList instances, as this method was missing in 1.4.

size

public int size()

Description copied from interface: Collection

Returns the number of elements in this collection. If this collection contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Specified by:

size in interface Collection

Returns:

the number of elements in this collection

isEmpty

public boolean isEmpty()

Description copied from interface: Collection

Returns true if this collection contains no elements.

Specified by:

isEmpty in interface Collection

Returns:

true if this collection contains no elements

contains

public boolean contains(Object o)

Description copied from interface: Collection

Returns true if this collection contains the specified element. More formally, returns true if and only if this collection 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 collection is to be tested.

Returns:

true if this collection contains the specified element

toArray

public Object[] toArray()

Description copied from interface: Collection

Returns an array containing all of the elements in this collection. If the collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.

The returned array will be "safe" in that no references to it are maintained by this collection. (In other words, this method must allocate a new array even if this collection is backed by an array). The caller is thus free to modify the returned array.

This method acts as bridge between array-based and collection-based APIs.

Specified by:

toArray in interface Collection

Returns:

an array containing all of the elements in this collection

toArray

public Object[] toArray(Object[] a)

Description copied from interface: Collection

Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. If the collection fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this collection.

If this collection fits in the specified array with room to spare (i.e., the array has more elements than this collection), the element in the array immediately following the end of the collection is set to null. This is useful in determining the length of this collection only if the caller knows that this collection does not contain any null elements.)

If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.

Like the toArray method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs

Suppose l is a List known to contain only strings. The following code can be used to dump the list into a newly allocated array of String:

     String[] x = (String[]) v.toArray(new String[0]);
 

Note that toArray(new Object[0]) is identical in function to toArray().

Specified by:

toArray in interface Collection

Parameters:

a - the array into which the elements of this collection are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.

Returns:

an array containing the elements of this collection

toString

public String toString()

Description copied from class: Object

Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

 getClass().getName() + '@' + Integer.toHexString(hashCode())
 

Overrides:

toString in class Object

Returns:

a string representation of the object.

iterator

public Iterator iterator()

Description copied from interface: Collection

Returns an iterator over the elements in this collection. There are no guarantees concerning the order in which the elements are returned (unless this collection is an instance of some class that provides a guarantee).

Specified by:

iterator in interface Collection

Returns:

an Iterator over the elements in this collection

add

public boolean add(Object o)

Description copied from interface: Collection

Ensures that this collection contains the specified element (optional operation). Returns true if this collection changed as a result of the call. (Returns false if this collection does not permit duplicates and already contains the specified element.)

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

If a collection refuses to add a particular element for any reason other than that it already contains the element, it must throw an exception (rather than returning false). This preserves the invariant that a collection always contains the specified element after this call returns.

Specified by:

add in interface Collection

Parameters:

o - element whose presence in this collection is to be ensured.

Returns:

true if this collection changed as a result of the call

remove

public boolean remove(Object o)

Description copied from interface: Collection

Removes a single instance of the specified element from this collection, if it is present (optional operation). More formally, removes an element e such that (o==null ? e==null : o.equals(e)), if this collection contains one or more such elements. Returns true if this collection contained the specified element (or equivalently, if this collection changed as a result of the call).

Specified by:

remove in interface Collection

Parameters:

o - element to be removed from this collection, if present.

Returns:

true if this collection changed as a result of the call

containsAll

public boolean containsAll(Collection coll)

Description copied from interface: Collection

Returns true if this collection contains all of the elements in the specified collection.

Specified by:

containsAll in interface Collection

Parameters:

coll - collection to be checked for containment in this collection.

Returns:

true if this collection contains all of the elements in the specified collection

See Also:

Collection.contains(Object)

addAll

public boolean addAll(Collection coll)

Description copied from interface: Collection

Adds all of the elements in the specified collection to this collection (optional operation). 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 collection, and this collection is nonempty.)

Specified by:

addAll in interface Collection

Parameters:

coll - elements to be inserted into this collection.

Returns:

true if this collection changed as a result of the call

See Also:

Collection.add(Object)

removeAll

public boolean removeAll(Collection coll)

Description copied from interface: Collection

Removes all this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.

Specified by:

removeAll in interface Collection

Parameters:

coll - elements to be removed from this collection.

Returns:

true if this collection changed as a result of the call

See Also:

Collection.remove(Object), Collection.contains(Object)

retainAll

public boolean retainAll(Collection coll)

Description copied from interface: Collection

Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.

Specified by:

retainAll in interface Collection

Parameters:

coll - elements to be retained in this collection.

Returns:

true if this collection changed as a result of the call

See Also:

Collection.remove(Object), Collection.contains(Object)

clear

public void clear()

Description copied from interface: Collection

Removes all of the elements from this collection (optional operation). This collection will be empty after this method returns unless it throws an exception.

Specified by:

clear in interface Collection