'How to get the last value of an ArrayList
How can I get the last value of an ArrayList?
Solution 1:[1]
The following is part of the List interface (which ArrayList implements):
E e = list.get(list.size() - 1);
E is the element type. If the list is empty, get throws an IndexOutOfBoundsException. You can find the whole API documentation here.
Solution 2:[2]
There isn't an elegant way in vanilla Java.
Google Guava
The Google Guava library is great - check out their Iterables class. This method will throw a NoSuchElementException if the list is empty, as opposed to an IndexOutOfBoundsException, as with the typical size()-1 approach - I find a NoSuchElementException much nicer, or the ability to specify a default:
lastElement = Iterables.getLast(iterableList);
You can also provide a default value if the list is empty, instead of an exception:
lastElement = Iterables.getLast(iterableList, null);
or, if you're using Options:
lastElementRaw = Iterables.getLast(iterableList, null);
lastElement = (lastElementRaw == null) ? Option.none() : Option.some(lastElementRaw);
Solution 3:[3]
this should do it:
if (arrayList != null && !arrayList.isEmpty()) {
T item = arrayList.get(arrayList.size()-1);
}
Solution 4:[4]
I use micro-util class for getting last (and first) element of list:
public final class Lists {
private Lists() {
}
public static <T> T getFirst(List<T> list) {
return list != null && !list.isEmpty() ? list.get(0) : null;
}
public static <T> T getLast(List<T> list) {
return list != null && !list.isEmpty() ? list.get(list.size() - 1) : null;
}
}
Slightly more flexible:
import java.util.List;
/**
* Convenience class that provides a clearer API for obtaining list elements.
*/
public final class Lists {
private Lists() {
}
/**
* Returns the first item in the given list, or null if not found.
*
* @param <T> The generic list type.
* @param list The list that may have a first item.
*
* @return null if the list is null or there is no first item.
*/
public static <T> T getFirst( final List<T> list ) {
return getFirst( list, null );
}
/**
* Returns the last item in the given list, or null if not found.
*
* @param <T> The generic list type.
* @param list The list that may have a last item.
*
* @return null if the list is null or there is no last item.
*/
public static <T> T getLast( final List<T> list ) {
return getLast( list, null );
}
/**
* Returns the first item in the given list, or t if not found.
*
* @param <T> The generic list type.
* @param list The list that may have a first item.
* @param t The default return value.
*
* @return null if the list is null or there is no first item.
*/
public static <T> T getFirst( final List<T> list, final T t ) {
return isEmpty( list ) ? t : list.get( 0 );
}
/**
* Returns the last item in the given list, or t if not found.
*
* @param <T> The generic list type.
* @param list The list that may have a last item.
* @param t The default return value.
*
* @return null if the list is null or there is no last item.
*/
public static <T> T getLast( final List<T> list, final T t ) {
return isEmpty( list ) ? t : list.get( list.size() - 1 );
}
/**
* Returns true if the given list is null or empty.
*
* @param <T> The generic list type.
* @param list The list that has a last item.
*
* @return true The list is empty.
*/
public static <T> boolean isEmpty( final List<T> list ) {
return list == null || list.isEmpty();
}
}
Solution 5:[5]
The size() method returns the number of elements in the ArrayList. The index values of the elements are 0 through (size()-1), so you would use myArrayList.get(myArrayList.size()-1) to retrieve the last element.
Solution 6:[6]
Using lambdas:
Function<ArrayList<T>, T> getLast = a -> a.get(a.size() - 1);
Solution 7:[7]
There is no elegant way of getting the last element of a list in Java (compared to e.g. items[-1] in Python).
You have to use list.get(list.size()-1).
When working with lists obtained by complicated method calls, the workaround lies in temporary variable:
List<E> list = someObject.someMethod(someArgument, anotherObject.anotherMethod());
return list.get(list.size()-1);
This is the only option to avoid ugly and often expensive or even not working version:
return someObject.someMethod(someArgument, anotherObject.anotherMethod()).get(
someObject.someMethod(someArgument, anotherObject.anotherMethod()).size() - 1
);
It would be nice if fix for this design flaw was introduced to Java API.
Solution 8:[8]
If you can, swap out the ArrayList for an ArrayDeque, which has convenient methods like removeLast.
Solution 9:[9]
As stated in the solution, if the List is empty then an IndexOutOfBoundsException is thrown. A better solution is to use the Optional type:
public class ListUtils {
public static <T> Optional<T> last(List<T> list) {
return list.isEmpty() ? Optional.empty() : Optional.of(list.get(list.size() - 1));
}
}
As you'd expect, the last element of the list is returned as an Optional:
var list = List.of(10, 20, 30);
assert ListUtils.last(list).orElse(-1) == 30;
It also deals gracefully with empty lists as well:
var emptyList = List.<Integer>of();
assert ListUtils.last(emptyList).orElse(-1) == -1;
Solution 10:[10]
If you use a LinkedList instead , you can access the first element and the last one with just getFirst() and getLast() (if you want a cleaner way than size() -1 and get(0))
Implementation
Declare a LinkedList
LinkedList<Object> mLinkedList = new LinkedList<>();
Then this are the methods you can use to get what you want, in this case we are talking about FIRST and LAST element of a list
/**
* Returns the first element in this list.
*
* @return the first element in this list
* @throws NoSuchElementException if this list is empty
*/
public E getFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return f.item;
}
/**
* Returns the last element in this list.
*
* @return the last element in this list
* @throws NoSuchElementException if this list is empty
*/
public E getLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return l.item;
}
/**
* Removes and returns the first element from this list.
*
* @return the first element from this list
* @throws NoSuchElementException if this list is empty
*/
public E removeFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return unlinkFirst(f);
}
/**
* Removes and returns the last element from this list.
*
* @return the last element from this list
* @throws NoSuchElementException if this list is empty
*/
public E removeLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return unlinkLast(l);
}
/**
* Inserts the specified element at the beginning of this list.
*
* @param e the element to add
*/
public void addFirst(E e) {
linkFirst(e);
}
/**
* Appends the specified element to the end of this list.
*
* <p>This method is equivalent to {@link #add}.
*
* @param e the element to add
*/
public void addLast(E e) {
linkLast(e);
}
So , then you can use
mLinkedList.getLast();
to get the last element of the list.
Solution 11:[11]
A one liner that takes into account empty lists would be:
T lastItem = list.size() == 0 ? null : list.get(list.size() - 1);
Or if you don't like null values (and performance isn't an issue):
Optional<T> lastItem = list.stream().reduce((first, second) -> second);
Solution 12:[12]
In case you have a Spring project, you can also use the CollectionUtils.lastElement from Spring (javadoc), so you don't need to add an extra dependency like Google Guava.
It is null-safe so if you pass null, you will simply receive null in return. Be careful when handling the response though.
Here are somes unit test to demonstrate them:
@Test
void lastElementOfList() {
var names = List.of("John", "Jane");
var lastName = CollectionUtils.lastElement(names);
then(lastName)
.as("Expected Jane to be the last name in the list")
.isEqualTo("Jane");
}
@Test
void lastElementOfSet() {
var names = new TreeSet<>(Set.of("Jane", "John", "James"));
var lastName = CollectionUtils.lastElement(names);
then(lastName)
.as("Expected John to be the last name in the list")
.isEqualTo("John");
}
Note: org.assertj.core.api.BDDAssertions#then(java.lang.String) is used for assertions.
Solution 13:[13]
Since the indexing in ArrayList starts from 0 and ends one place before the actual size hence the correct statement to return the last arraylist element would be:
int last = mylist.get(mylist.size()-1);
For example:
if size of array list is 5, then size-1 = 4 would return the last array element.
Solution 14:[14]
guava provides another way to obtain the last element from a List:
last = Lists.reverse(list).get(0)
if the provided list is empty it throws an IndexOutOfBoundsException
Solution 15:[15]
This worked for me.
private ArrayList<String> meals;
public String take(){
return meals.remove(meals.size()-1);
}
Solution 16:[16]
The last item in the list is list.size() - 1. The collection is backed by an array and arrays start at index 0.
So element 1 in the list is at index 0 in the array
Element 2 in the list is at index 1 in the array
Element 3 in the list is at index 2 in the array
and so on..
Sources
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Source: Stack Overflow