public class ListUtils extends Object
List instances.| Modifier and Type | Field and Description |
|---|---|
static List |
EMPTY_LIST
An empty unmodifiable list.
|
| Constructor and Description |
|---|
ListUtils()
ListUtils should not normally be instantiated. |
| Modifier and Type | Method and Description |
|---|---|
static List |
fixedSizeList(List list)
Returns a fixed-sized list backed by the given list.
|
static int |
hashCodeForList(Collection list)
Generates a hash code using the algorithm specified in
List.hashCode(). |
static List |
intersection(List list1,
List list2)
Returns a new list containing all elements that are contained in
both given lists.
|
static boolean |
isEqualList(Collection list1,
Collection list2)
Tests two lists for value-equality as per the equality contract in
List.equals(java.lang.Object). |
static List |
lazyList(List list,
Factory factory)
Returns a "lazy" list whose elements will be created on demand.
|
static List |
predicatedList(List list,
Predicate predicate)
Returns a predicated (validating) list backed by the given list.
|
static List |
removeAll(Collection collection,
Collection remove)
Removes the elements in
remove from collection. |
static List |
retainAll(Collection collection,
Collection retain)
Returns a List containing all the elements in
collection
that are also in retain. |
static List |
subtract(List list1,
List list2)
Subtracts all elements in the second list from the first list,
placing the results in a new list.
|
static List |
sum(List list1,
List list2)
Returns the sum of the given lists.
|
static List |
synchronizedList(List list)
Returns a synchronized list backed by the given list.
|
static List |
transformedList(List list,
Transformer transformer)
Returns a transformed list backed by the given list.
|
static List |
typedList(List list,
Class type)
Returns a typed list backed by the given list.
|
static List |
union(List list1,
List list2)
Returns a new list containing the second list appended to the
first list.
|
static List |
unmodifiableList(List list)
Returns an unmodifiable list backed by the given list.
|
public static final List EMPTY_LIST
Collections implementation
and is provided for completeness.public static List intersection(List list1, List list2)
list1 - the first listlist2 - the second listNullPointerException - if either list is nullpublic static List subtract(List list1, List list2)
This differs from List.removeAll(Collection) in that
cardinality is respected; if list1 contains two
occurrences of null and list2 only
contains one occurrence, then the returned list will still contain
one occurrence.
list1 - the list to subtract fromlist2 - the list to subtractNullPointerException - if either list is nullpublic static List sum(List list1, List list2)
list1 - the first listlist2 - the second listNullPointerException - if either list is nullpublic static List union(List list1, List list2)
List.addAll(Collection) operation is
used to append the two given lists into a new list.list1 - the first listlist2 - the second listNullPointerException - if either list is nullpublic static boolean isEqualList(Collection list1, Collection list2)
List.equals(java.lang.Object).
This method is useful for implementing List when you cannot
extend AbstractList. The method takes Collection instances to enable other
collection types to use the List implementation algorithm.
The relevant text (slightly paraphrased as this is a static method) is:
Compares the two list objects for equality. Returns true if and only if 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.Note: The behaviour of this method is undefined if the lists are modified during the equals comparison.
list1 - the first list, may be nulllist2 - the second list, may be nullListpublic static int hashCodeForList(Collection list)
List.hashCode().
This method is useful for implementing List when you cannot
extend AbstractList. The method takes Collection instances to enable other
collection types to use the List implementation algorithm.
list - the list to generate the hashCode for, may be nullList.hashCode()public static List retainAll(Collection collection, Collection retain)
collection
that are also in retain. The cardinality of an element e
in the returned list is the same as the cardinality of e
in collection unless retain does not contain e, in which
case the cardinality is zero. This method is useful if you do not wish to modify
the collection c and thus cannot call collection.retainAll(retain);.collection - the collection whose contents are the target of the #retailAll operationretain - the collection containing the elements to be retained in the returned collectionList containing all the elements of c
that occur at least once in retain.NullPointerException - if either parameter is nullpublic static List removeAll(Collection collection, Collection remove)
remove from collection. That is, this
method returns a list containing all the elements in c
that are not in remove. The cardinality of an element e
in the returned collection is the same as the cardinality of e
in collection unless remove contains e, in which
case the cardinality is zero. This method is useful if you do not wish to modify
collection and thus cannot call collection.removeAll(remove);.collection - the collection from which items are removed (in the returned collection)remove - the items to be removed from the returned collectionList containing all the elements of c except
any elements that also occur in remove.NullPointerException - if either parameter is nullpublic static List synchronizedList(List list)
You must manually synchronize on the returned buffer's iterator to avoid non-deterministic behavior:
List list = ListUtils.synchronizedList(myList);
synchronized (list) {
Iterator i = list.iterator();
while (i.hasNext()) {
process (i.next());
}
}
This method uses the implementation in the decorators subpackage.list - the list to synchronize, must not be nullIllegalArgumentException - if the list is nullpublic static List unmodifiableList(List list)
This method uses the implementation in the decorators subpackage.
list - the list to make unmodifiable, must not be nullIllegalArgumentException - if the list is nullpublic static List predicatedList(List list, Predicate predicate)
Only objects that pass the test in the given predicate can be added to the list. Trying to add an invalid object results in an IllegalArgumentException. It is important not to use the original list after invoking this method, as it is a backdoor for adding invalid objects.
list - the list to predicate, must not be nullpredicate - the predicate for the list, must not be nullIllegalArgumentException - if the List or Predicate is nullpublic static List typedList(List list, Class type)
Only objects of the specified type can be added to the list.
list - the list to limit to a specific type, must not be nulltype - the type of objects which may be added to the listpublic static List transformedList(List list, Transformer transformer)
Each object is passed through the transformer as it is added to the List. It is important not to use the original list after invoking this method, as it is a backdoor for adding untransformed objects.
list - the list to predicate, must not be nulltransformer - the transformer for the list, must not be nullIllegalArgumentException - if the List or Transformer is nullpublic static List lazyList(List list, Factory factory)
When the index passed to the returned list's get
method is greater than the list's size, then the factory will be used
to create a new object and that object will be inserted at that index.
For instance:
Factory factory = new Factory() {
public Object create() {
return new Date();
}
}
List lazy = ListUtils.lazyList(new ArrayList(), factory);
Object obj = lazy.get(3);
After the above code is executed, obj will contain
a new Date instance. Furthermore, that Date
instance is the fourth element in the list. The first, second,
and third element are all set to null.list - the list to make lazy, must not be nullfactory - the factory for creating new objects, must not be nullIllegalArgumentException - if the List or Factory is nullpublic static List fixedSizeList(List list)
List.set(int,Object) method).list - the list whose size to fix, must not be nullIllegalArgumentException - if the List is nullCopyright © 2001–2015 The Apache Software Foundation. All rights reserved.