Jan 20, 2013 · With your declaration JVM will create a ArrayList of integer arrays i.e each entry in arraylist correspond to an integer array hence your add function should pass a integer array as a parameter. For Ex:

Jan 10, 2013 · Thus, your ArrayList<Number> doesn't contain java.lang.Number, but another type entirely. Therefore, you can't add an int to it; the compiler cannot convert an int into an instance of the custom Number class. Instead, you need to explicitly create an instance of your Number class, or get rid of it and use java.lang.Number.

If you want the number of unique items and your items implement equals and hashCode correctly you can put them all in a set and call size on that, like this: new HashSet<>(list).size() If you want the number of items with a distinct itemId you can do this: list.stream().map(i -> i.itemId).distinct().count()

Feb 3, 2009 · import java.util.*; public class CountItemsList<E> extends ArrayList<E> { // This is private. It is not visible from outside. private Map<E,Integer> count = new HashMap<E,Integer>(); // There are several entry points to this class // this is just to show one of them.

Jul 13, 2022 · Better to use a HashSet than an ArrayList when you are checking for existence of a value. Java docs for HashSet says. This class offers constant time performance for the basic operations (add, remove, contains and size) ArrayList.contains() might have to iterate the whole list to find the instance you are looking for.

Mar 24, 2016 · You can find the smallest value of an ArrayList using the following ways in JAVA ARRAY List: way 1. Find the smallest value of an ArrayList using the Collection class. Find the smallest value of an ArrayList using the Collection class.

I need to separate and count how many values in arraylist are the same and print them according to the number of occurrences. I've got an arraylist called digits : [1, 1, 2, 3, 5, 8, 13, 21, 34,...

Aug 13, 2017 · Returns the number of elements in this list. If this list contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE. So, no limit, but after you reach Integer.MAX_VALUE, the behaviour of the list changes a bit. ArrayList (which is tagged) is backed by an array, and is limited to the size of the array - i.e. Integer.MAX_VALUE

Aug 14, 2009 · List<String> subItems = new ArrayList<String>(items.subList(0, 2)); If the list is shorter than the specified size, expect an out of bounds exception. Choose the minimum value of the desired size and the current size of the list as the ending index. Lastly, note that the second argument should be one more than the last desired index.

they're actually about as fast in properly done test. interestingly enough the "enhanced for loop" and the traditional for loop ends up being executed just as fast as a while(i-->0) one, despite having an extra evaluation/call per loop. this just running on se1.7, with the arraylist filled with objects having a random int as member variable and ...