That these operations may execute in time proportional to the index valueįor some implementations (the LinkedList class, forĮxample). The List interface provides four methods for positional (indexed)Īccess to list elements. Declarations for other inherited methods are Specified in the Collection interface, on the contracts of the The List interface places additional stipulations, beyond those Throwing runtime exceptions when the user attempts to insert them, but we That someone might wish to implement a list that prohibits duplicates, by Null elements if they allow null elements at all. Such that e1.equals(e2), and they typically allow multiple Lists typically allow pairs of elements e1 and e2 Unlike sets, lists typically allow duplicate elements. The list), and search for elements in the list. The user can access elements by their integer index (position in Interface has precise control over where in the list each element is And if the complexity of the System.arraycopy was O(N), overall complexity would still be O(M+N).An ordered collection (also known as a sequence). Imagine System.arraycopy is O(1), the complexity of the whole function would still be O(M+N). But even if the implementation of this had better time complexity, the overall time complexity of the addAll function would not change. I didn't see the source code of the System.arraycopy function, but the easiest and most intuitive way of implementing an array copy is iterating over all elements, which makes it O(N) again. Finally, it uses System.arraycopy to copy the array of new elements (of the Collection) into the grown array (of the ArrayList).In the worst case scenario, the array (of the ArrayList) doesn't have enough capacity to "accommodate" the new elements to be added, so it needs to create a copy of the current elements into a new bigger array (O(M)).If the collections is for example a LinkedList, this means it needs to iterate over all the elements and insert it into a new array, so this is already O(N). In the very first line of code, it converts collection to array.System.arraycopy(a, 0, elementData, s, numNew) If (numNew > (elementData = this.elementData).length - (s = size)) * NullPointerException if the specified collection is null * true} if this list changed as a result of the call * c collection containing elements to be added to this list * undefined if the specified collection is this list, and this (This implies that the behavior of this call is * undefined if the specified collection is modified while the operation * this list, in the order that they are returned by the * Appends all of the elements in the specified collection to the end of Just curious how about the complexity of ArrayList.addAll(Collection)? is it Constant nope, it's O(M+N) where M = array size (the ArrayList) and N = collection size (the function argument Collection).įYI, the source code of ArrayList.addAll in JDK 11: /** TreeMap | O( log n) | O( log n) | O( log n) | Red- black treeĬoncurrentHashMap | O( 1) | O( 1) | O( h / n) | Hash TablesĬoncurrentSkipListMap | O( log n) | O( log n) | O( 1) | Skip List WeakHashMap | O( 1) | O( 1) | O( h / n) | Hash Table IdentityHashMap | O( 1) | O( 1) | O( h / n) | Array LinkedHashMap | O( 1) | O( 1) | O( 1) | Hash Table + Linked List HashMap | O( 1) | O( 1) | O( h / n) | Hash Table Map | Get | ContainsKey | Next | Data Structure LinkedBlockingQueue | O( 1) | O( 1) | O( 1) | O( n) | O( 1) | Linked List SynchronousQueue | O( 1) | O( 1) | O( 1) | O( n) | O( 1) | None!ĭelayQueue | O( log n) | O( 1) | O( log n) | O( n) | O( 1) | Priority Heap PriorirityBlockingQueue | O( log n) | O( 1) | O( log n) | O( n) | O( 1) | Priority Heap PriorityQueue | O( log n) | O( 1) | O( log n) | O( n) | O( 1) | Priority Heap Queue | Offer | Peak | Poll | Remove | Size | Data Structure TreeSet | O( log n) | O( log n) | O( log n) | O( log n) | O( 1) | Red- black treeĬopyOnWriteArraySet | O( n) | O( n) | O( n) | O( 1) | O( 1) | ArrayĬoncurrentSkipListSet | O( log n) | O( log n) | O( log n) | O( 1) | O( n) | Skip List Set | Add | Remove | Contains | Next | Size | Data Structure LinkedList | O( 1) | O( 1) | O( n) | O( n) | O( 1) | Linked ListĬopyOnWriteArrayList | O( n) | O( n) | O( 1) | O( n) | O( 1) | Array List | Add | Remove | Get | Contains | Next | Data Structure Below are the Big O performance of common functions of different Java Collections.
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