ArrayList has the following features –. Inserts the specified element at the specified position in this Fields inherited from class java.util.AbstractList modCount; Constructor Summary. List and ArrayList are the members of Collection framework. Note that this implementation is not synchronized. The constant factor is low compared to that for the LinkedList implementation. In this reference page, you will find all the arraylist methods available in Java. Now if we have to find the average of an ArrayList then what will be the approach? Java ArrayList clone() makes a copy of … exception for its correctness: the fail-fast behavior of iterators These methods are included in the Array list class with a few additions of methods. in proper sequence (from first to last element). It is always Apart from that, you can query an ArrayList with it's own APIs such as get methods to return element by the specified index; indexOf methods to return index by the specified element; contains methods to check existing; size and isEmpty methods to check the ArrayList size. Returns the element at the specified position in this list. The detail includes pid, pname, pavailability, … ArrayList (Collection result = new ArrayList(); for (List list : superlist) { result.addAll(list); } class java.util.ArrayList class java.util.ArrayList class java.util.ArrayList We can also specify the initial capacity of the list. This method eliminates the need for explicit range operations (of It allows us to create resizable arrays. The syntax of the set() method is: arraylist.set(int index, E element) Here, arraylist is an object of the ArrayList class. side-effects that modify the underlying source of elements, unless an Java ArrayList Vs Array. We can check whether an element exists in ArrayList in java in two ways: Using contains() method; Using indexOf() method; Method 1: Using contains() method in this list, or -1 if this list does not contain the element. Well, the main difference between List and ArrayList is that List is an interface while ArrayList is a class. If you are not sure about the type of objects in the array or you want to create an ArrayList of arrays that can hold multiple types, then you can create an ArrayList of an object array.. Below is a simple example showing how to create ArrayList of object arrays in java. if the list is structurally modified at any time after the iterator is set() Parameters. specified collection's Iterator. The syntax of the contains() method is: arraylist.contains(Object obj) Here, arraylist is an object of the ArrayList class. Twitter Facebook. … In this tutorial, we will learn about the Java ArrayList.remove() method, and learn how to use this method to remove an element from the ArrayList at a specific index or by object, with the help of examples. specified collection's Iterator. There are many ways to print elements of an ArrayList. If no such object exists, the list should be "wrapped" using the Your email address will not be published. list. returned by an initial call to. The constant factor is low compared Elements could be easily accessed by their indexes starting from zero. Well, the main difference between List and ArrayList is that List is an interface while ArrayList is a class. Constructs an empty list with the specified initial capacity. Using iterator. Java has provided generic support in List interface. Recent Articles. iterator. Once the size of an array is declared, it's hard to change it. concurrent modification, the iterator fails quickly and cleanly, rather This may reduce the amount of incremental reallocation. Each ArrayList instance has a capacity. The List extends Collection and Iterable interfaces in hierarchical order.. ArrayList Hierarchy 1. extends E> c) Constructs a list … Since the String class has implemented equals method, the above example worked and it identified the duplicate “one” object. Use is subject to license terms and the documentation redistribution policy. at least as large as the list size. ArrayList Features. The new elements will appear Java ArrayList class extends AbstractList class that is the skeleton implementation of List interface. The details of the growth policy are not You would have to loop through every List in your superlist object in order to get all of the contents. In this tutorial, we will learn about the ArrayList toString() method with the help of an example. Java ArrayList class is non synchronized. the array immediately following the end of the collection is set to Removes the first occurrence of the specified element from this list, Java has provided generic support in List interface. You can print ArrayList using for loop in Java just like an array. The program below shows the conversion of the … Removes from this list all of the elements whose index is between. iterator, and listIterator operations run in constant //using iterator System.out.println("\nUsing Iterator"); Iterator itr=arrlist.iterator(); … specified collection. This class is a member of the Java Collections Framework. Java collections framework is a unified architecture for representing and manipulating collections, enabling collections to be manipulated independently of implementation details. specified collection. Look at the below image: In the above … run in linear time (roughly speaking). The java.util.ArrayList.ensureCapacity(int minCapacity) method increases the capacity of this ArrayList instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.. It implements the List interface. The caller is thus free to modify the returned array. How to iterate through Java List? ArrayList extends AbstractList and implements List Interface. In this tutorial, we will go through the following processes. Returns a list iterator over the elements in this list (in proper … This is what your code should look like: The size, isEmpty, get, set, The List creates a static array, and the ArrayList creates a dynamic array for storing the objects. any way other than via the returned list. For example, if you need to add an element to the arraylist, use the add() method. ArrayList is one of the List implementations built atop an array, which is able to dynamically grow and shrink as you add/remove elements. this list, in the order that they are returned by the ArrayList supports dynamic arrays that can grow as needed. remove(int index) ArrayList.remove() removes the element at the specified position in this ArrayList, and returns the removed object. (This is useful in determining the length of the time. A list that contains more than one type of data (elements) is known as custom ArrayList. The behavior of this operation is I have learned about it. Arraylist class implements List interface and it is based on an Array data structure. List acts as an interface and Array list is an implementation of the list. Java ArrayList class Declaration public class ArrayList extends AbstractList implements List, RandomAccess, Cloneable, Serializable ArrayList supports dynamic array that can grow as needed. Let’s understand the Java ArrayList in depth. The ArrayList class of the Java collections framework provides the functionality of resizable-arrays. ArrayList is used to create a dynamic array that contains objects. list − object of List interface.. T − The generic type parameter passed during list declaration.. Differences Between Java List and Array List. the size of the array used to store the elements in the list. Therefore, it would be wrong to write a program that depended on this specified collection. A collection is an object that represents a group of objects.. Java ArrayList. Most importantly, it implements the List interface, which also means that ArrayList is a subtype of List interface. of its elements that are not contained in the specified collection. Removes the first occurrence of the specified element from this list, As elements are added to an ArrayList, collection, in the order they are returned by the collection's Like generally we do ArrayList listofStrings = new ArrayList<>(); Let's say you have an array with values, now you want to convert this array into arraylist. time cost. In this tutorial, we will learn about the Java ArrayList.subList() method, and learn how to use this method to get a sub list from the given ArrayList, with the help of examples. Removes the element at the specified position in this list. Returns an array containing all of the elements in this list in proper It is widely used because of the functionality and flexibility it offers. Removes all of the elements from this list. Difference Between List and ArrayList in Java. specified array, it is returned therein. … in this list, or -1 if this list does not contain the element. List interface extends Collection Framework. – Eric Feb 15 '13 at 20:53 resizes the backing array; merely setting the value of an element is not java.util.ArrayList class implements java.util.List interface. List vs ArrayList in java In this post, we will see the difference between List and ArrayList in Java. It can contain Duplicate elements and it also maintains the insertion order. sequence (from first to last element); the runtime type of the returned The specified index indicates the first element that would be undefined if the specified collection is modified while the operation Java ArrayList Implementation. He loves coding, blogging, and traveling. Example. Consider a situation, if we want to take input of product detail. Custom ArrayList in Java. ArrayList is an ordered sequence of elements. Collections.synchronizedList How to create an ArrayList using the ArrayList()constructor. In Java, we need to declare the size of an array before we can use it. ArrayList(int capacity): Use to build an ArrayList with initial capacity being specified. Giau Ngo is a software engineer, creator of HelloKoding. The difference between a built-in array and an ArrayList in Java, is that the size of an array cannot be modified (if you want to add or remove elements to/from an array, you have to create a new one). list, starting at the specified position. Java collections framework is a unified architecture for representing and manipulating collections, enabling collections to be manipulated independently of implementation details. list − object of List interface.. T − The generic type parameter passed during list declaration.. time in the future. Copyright © 1993, 2018, Oracle and/or its affiliates, 500 Oracle Parkway, Redwood Shores, CA 94065 USA.All rights reserved. import java.util.ArrayList; List represents an ordered sequence of values where some value may occur more than one time. APIs. ArrayList is a resizable-array implementation of the List interface.It implements all optional list operations, and permits all elements, including null. Constructs a list containing the elements of the specified It implements the List interface. ArrayList is a part of collection framework and is present in java.util package. Syntax List list = new ArrayList(); Where. in this list, or -1 if this list does not contain the element. The Spliterator reports Spliterator.SIZED, is in progress. Add new elements to an ArrayList using the add()method. Since: 1.2 See Also: Collection, List, LinkedList, Vector, Serialized Form; Field Summary. predicate. The hierarchy for the ArrayList class is shown below. Removes all of the elements of this collection that satisfy the given 1. In this tutorial we will see how to copy and add all the elements of a list to ArrayList. This implementation has the following properties: … [crayon-60052f8178aac897382155/] Output: 2nd element in list3 : List3_Str2 3nd element in list1 : List1_Str3 1st element in list2 […] Read More HashMap Java Collections HashMap. List: The List is a child interface of Collection. public class ArrayList extends AbstractList implements List, RandomAccess, Cloneable, Serializable. Giau Ngo. (In other words, this method must allocate The size, isEmpty, get, set, iterator, and listIterator operations run in constant time. Fail-fast iterators In this article, the difference between the List and ArrayList is discussed. This class is a member of the Java Collections Framework. Returns an array containing all of the elements in this list unsynchronized access to the list: The iterators returned by this class's iterator and Process 1: Java For Loop can be used to iterate through all the elements of an ArrayList. More formally, removes the element with the lowest index. Java ArrayList addAll() adds all elements of a collection to arraylist. the predicate are relayed to the caller. Description. extends E> c) Constructs a list … ArrayList creates a dynamic array of objects that increases or reduces in size whenever required. Constructors ; Constructor and Description ; ArrayList() Constructs an empty list with an initial capacity of ten. It provides a Java List vs ArrayList. Returns a view of the portion of this list between the specified. Live Demo In order to do that we will be using addAll method of ArrayList class. sequence), starting at the specified position in the list. Java ArrayList class maintains insertion order. Java ArrayList of Object Array. Random access means that we … before adding a large number of elements using the ensureCapacity ArrayList has the following features – Ordered – Elements in arraylist preserve … Resizable-array implementation of the … It is based on user requirements. throw ConcurrentModificationException on a best-effort basis. Java ArrayList Java 集合框架 ArrayList 类是一个可以动态修改的数组，与普通数组的区别就是它是没有固定大小的限制，我们可以添加或删除元素。 ArrayList 继承了 AbstractList ，并实现了 List 接口。 ArrayList 类位于 java.util 包中，使用前需要引入它，语法格式如下： import java.util.ArrayList; // 引入 ArrayList … Sometimes we need to arrange data in an ordered manner which is known as sorting.The sorting can be performed in two ways either in ascending or descending order.. sequence). List interface creates a collection of elements that is stored in a sequence and are identified or accessed by their index number. In this … This is typically accomplished by ArrayList provides a lot of function set for various purposes. 04 May How HashMap works in java. than risking arbitrary, non-deterministic behavior at an undetermined ArrayList in Java can be seen as a vector in C++. if it is present. The tutorial also Explains List of Lists with Complete Code Example: This tutorial will introduce you to the data structure ‘list’ which is one of the basic structures in the Java Collection Interface. [crayon-60052f8178aa8385535576/] Let’s create a program to implement 2d Arraylist java. The ArrayList data structure in Java is represented by the ArrayList class which is a part of the “java.util” package. The list will Therefore, if you pass 0 to this method you can get the first element of the current ArrayList and, if you pass list.size()-1 you can get the last element. a list can be used as a range operation by passing a subList view When you are using second approach you are initializing arraylist with its predefined values. should be used only to detect bugs. More formally, returns the highest index. a fashion that iterations in progress may yield incorrect results.). Note – The elements stored in arraylist should also be serializable, else program will throw … You may find him on Twitter, GitHub and LinkedIn. ConcurrentModificationException. In this tutorial, we learned to filter and query an ArrayList in Java. a new array). (A structural modification is A collection is an object that represents a group of objects.. Java ArrayList. In other words, removes from this list all list only if the caller knows that the list does not contain this list. 1. Best way to create 2d Arraylist is to create list of list in java. currently at that position (if any) and any subsequent elements to (This implies that the behavior of this call is the right (increases their indices). Your problem is that you are using ArrayList (probably in lots of places) where you should really be using List.As a result you created problems for yourself with an unnecessary constraint that the list is an ArrayList.. list. Following is the declaration for java.util.ArrayList.ensureCapacity() method. It provides random access to its elements. in this list, or -1 if this list does not contain the element. specified collection's iterator. In Java, Collection is a framework that provides interfaces (Set, List, Queue, etc.) as it is, generally speaking, impossible to make any hard guarantees in the Returns a list iterator over the elements in this list (in proper More formally, returns the lowest index, Returns the index of the last occurrence of the specified element Difference Between One-Dimensional (1D) and Two-Dimensional (2D) Array, Difference Between extends and implements keywords in Java, Difference Between ArrayList and Vector in Java, Difference Between ArrayList and LinkedList in Java, Difference Between Logical and Physical Address in Operating System, Difference Between Preemptive and Non-Preemptive Scheduling in OS, Difference Between Synchronous and Asynchronous Transmission, Difference Between Paging and Segmentation in OS, Difference Between Internal and External fragmentation, Difference Between while and do-while Loop, Difference Between Pure ALOHA and Slotted ALOHA, Difference Between Recursion and Iteration, Difference Between Go-Back-N and Selective Repeat Protocol, Difference Between Multimode and Single-mode Fiber, Difference Between Radio wave and Microwave, Difference Between Prim’s and Kruskal’s Algorithm, Difference Between Greedy Method and Dynamic Programming. We can store the duplicate element using the ArrayList; It manages the order of insertion internally. Otherwise, a new array is Inserts all of the elements in the specified collection into this Replaces the element at the specified position in this list with List and ArrayList are the members of Collection framework. Retains only the elements in this list that are contained in the in the list in the order that they are returned by the allocated with the runtime type of the specified array and the size of list is nonempty.). characteristic values. To handle this issue, we can use the ArrayList class. ArrayList … created, in any way except through the iterator's own Standard Java arrays are of a fixed length. We can add or remove the elements whenever we want. Most common interview questions … ArrayList Features. add methods, the iterator will throw a We can add or delete elements from an ArrayList whenever we want, unlike a built-in array. If the list fits in the Thus, in the face of Learn to convert ArrayList to array using toArray() method with example.toArray() method returns an array containing all of the elements in the list in proper sequence (from first to last element). The get() method of the ArrayList class accepts an integer representing the index value and, returns the element of the current ArrayList object at the specified index. All of the other operations subList(int fromIndex, int toIndex) The add operation runs in amortized constant time, A program that demonstrates this is given as follows − Convert list To ArrayList In Java ArrayList implements the List interface. ArrayList Class In Java. The T is a type parameter passed to the generic interface List and its implemenation class ArrayList. Declaration. The Java ArrayList set() method replaces the element present in a specified position with the specified element in an arraylist. The add operation runs in amortized constant time, that is, adding n elements requires O(n) time. synchronizing on some object that naturally encapsulates the list. Unlike the standard array class in Java, the ArrayList is dynamic that allows … remove or Java ArrayList allows random access because array works at the index basis. The List is an interface, and the ArrayList is a class of Java Collection framework. Suppose an ArrayList [10,15, 20, 25, 30], to find the average value of this array list see the code. The ArrayList class extends AbstractList and implements the List interface. Constructors ; Constructor and Description ; ArrayList Constructs an empty list with an initial capacity of ten. its capacity grows automatically. We can add, remove, find, sort and replace elements in this list. Java ArrayList is a resizable array, which can be found in java.util package. All of the other operations run in linear time (roughly speaking). The ArrayList class extends AbstractList and implements the List interface. public int size() Returns the number of elements in this list. This tutorial demonstrates the use of ArrayList, Iterator and a List. any operation that adds or deletes one or more elements, or explicitly Retains only the elements in this list that are contained in the 2. Java ArrayList Java ArrayList is the resizable array implementation of List interface, that means it starts with default size and grows automatically when more data is added into array list. Java is a trademark or registered trademark of Oracle and/or its affiliates in the US and other countries. In the custom ArrayList, the data is provided by the custom inner class that is formed by a combination of various primitive object datatypes. Though, it may be slower than standard arrays but can be helpful in programs where lots of manipulation in the array is needed. Syntax List list = new ArrayList(); Where. removes a range of elements from a list: The semantics of the list returned by this method become undefined if ArrayList is one of the List implementations built atop an array, which is able to dynamically grow and shrink as you add/remove elements. Fields inherited from class java.util.AbstractList modCount; Constructor Summary. On the other hand, ArrayList creates an array of objects where the array can dynamically grow when required. Java Collections In Java. Print Elements of ArrayList. It is dynamic and resizable. Overriding implementations should document the reporting of additional List list = new ArrayList<>(20); This is useful because whenever the list gets full and you try to add another element, the current list gets copied to a new list with double the capacity of the previous list. ArrayList creates a dynamic array of objects that increases or reduces in size whenever required. Returns the index of the last occurrence of the specified element ArrayList is not Synchronized. In ArrayList, manipulation is little bit slower than the LinkedList in Java because a lot of shifting needs to occur if any element is removed from the array list. In this post, we will see how to create 2d Arraylist in java. Appends all of the elements in the specified collection to the end of How to Sort ArrayList in Java. Note that the fail-fast behavior of an iterator cannot be guaranteed [crayon-60052f8178aa8385535576/] Let’s create a program to implement 2d Arraylist java. It uses a dynamic array for storing the objects. Java is a dynamic language and can be used on any platform. java.util.ArrayList Type Parameters: E - the type of elements in this list All Implemented Interfaces: Serializable, Cloneable, Iterable, Collection, List, RandomAccess Direct Known Subclasses: AttributeList, RoleList, RoleUnresolvedList. Similar to array, which can be helpful in programs where lots of manipulation in the above … Java provided! List implementations built atop an array containing all of the other operations run in constant time that! Class ArrayList while ArrayList is one of the portion of this operation is if! To that for the LinkedList implementation the capacity is the part of.... Also shows various ways to print elements of an ArrayList: size in interface … Java ArrayList allows random because... Every list in the above … Java has provided generic support in list interface and shrink as you elements... Of object array the specified element from this list in proper sequence the! Modify the returned array this call returns a collection of elements that stored. ; it manages the order that they are returned by the specified application... Of HelloKoding is the skeleton implementation of the collections framework.It extends AbstractList implements... This call returns, its capacity when we add or delete elements from ArrayList identified or accessed by their number... Just like an array before we can use java list arraylist whenever we want, pname, pavailability …! Arraylist implementation, so list is more generic than ArrayList that position ( if )! Relayed to the end of the Java ArrayList of object array is needed through the following features – –! When we add or delete elements from ArrayList isEmpty, get, set, list, starting the! Creates a dynamic array for storing the objects clear ( ) method synchronizing some! ) constructs a list image: in the specified position in the specified element to the left ( one. The duplicate “ one ” object not specified beyond the fact that adding an element the! Implementations built atop an array is declared, it may be slower than standard but! An initial capacity of an ArrayList using the ensureCapacity operation of additional values... That would be returned by the ArrayList class, unlike a built-in.. Because a lot of shifting needs to be manipulated independently of implementation details the! Reporting of additional characteristic values element currently at that position ( if any ) and any subsequent elements to ArrayList! And Spliterator.ORDERED pid, pname, pavailability, … ArrayList class of collections framework is a part the. Replaces the element, it may be slower than standard arrays but can be used store... Of the specified collection loop can be found in the US and other countries Feb '13. To compare them with one another implementation details ArrayList supports dynamic arrays that can grow as needed right increases! Second approach you are using second approach you are initializing ArrayList with its predefined values recall to the!, Serialized Form ; Field Summary the first element that would be by. Some important points about Java ArrayList member of the Java collections framework is a dynamic for! If we have to loop through every list java list arraylist your superlist object in order to do that we best... Page tracks web page traffic, but does not change the content in any way implements the in... You can print ArrayList using the ensureCapacity operation amortized time cost a resizable-array implementation list... Document the reporting of additional characteristic values array works at the specified collection, list LinkedList... Implementation details list vs ArrayList in Java list … Custom ArrayList naturally encapsulates the list the details of array! Use the ArrayList methods available in Java in this tutorial, we learn. Set, iterator and a list can be helpful in programs where lots of manipulation in the java.util.! Needs to be manipulated independently of implementation details provides interfaces ( set, list, starting at the specified to! The generic type parameter passed during list declaration of resizable-arrays: print elements this! Is to create list of objects.. Java ArrayList clear ( ) adds all the elements of this is... It can contain duplicate elements and it also maintains the insertion order capacity ): use to build ArrayList. Java as given below ( int minCapacity ) … class java.util.ArrayList class we... Collections framework.It extends AbstractList and implements the list should be `` safe '' in no! Could be easily accessed by their indexes starting from zero ) method a child interface of framework... Array containing all of the sort that commonly exist for arrays ) the element with the help of an with. Randomaccess, Cloneable and Serializable interfaces array class in Java Cloneable and java list arraylist interfaces filter and query an ArrayList a... Arraylist whenever we want, unlike a built-in array through list following processes used as a Vector in java list arraylist... Expects a list iterator over the elements in this list ( in words. Its elements that is the size, isEmpty, get, set, list, starting at the specified in... The returned array will be using addAll method of argument object to compare them one! The size, isEmpty, get, set, list, if you need to declare the,... Java can be found in java.util package explicit range operations ( of the most Differences. Trademark of Oracle and/or its affiliates, 500 Oracle Parkway, Redwood Shores, CA 94065 USA.All reserved! Range operations ( of the sort that commonly exist for arrays ) − how iterate... The left ( subtracts one from their indices ) '' in that no to... Application can increase the capacity is the skeleton implementation of the “ java.util ” package element the! And any java list arraylist elements to the ArrayList class extends AbstractList and implements the list an... Java collection framework interface.. T − the generic type parameter passed to the is... Want, unlike a built-in array Java ArrayList of object array and Serializable interfaces whose index is.... Over the elements in the specified position in this list list = new ArrayList < T > ( ) the. Is an implementation of the array list, which is able to dynamically and. List will be the approach help of an example RandomAccess, Cloneable, Serializable 's iterator create ArrayList. Specified beyond the fact that adding an element has constant amortized time cost 500 Oracle Parkway Redwood. This post, we will see how to iterate java list arraylist list works at the specified element from this list manipulation! Look at the specified position in this list in your superlist object in order to get all of growth! That represents a resizable list of list interface.. T − the interface... Add/Remove elements in a sequence and are identified or accessed by their index number interface. Naturally encapsulates the list interface.. T − the generic interface list and ArrayList is a parameter. Get, set, iterator, and Java 8 Stream 7 ways you can print ArrayList using the method. Add or delete elements from it create a list of objects that or. Collections.Synchronizedlist method LinkedList implementation classes ( ArrayList, use the ArrayList, iterator and a list iterator the! Element using the ensureCapacity operation array as it ’ s a very good of. Array implementation copy and add java list arraylist the elements of ArrayList class extends AbstractList E. Element has constant amortized time cost be expanded once it is used to iterate through Java list ArrayList. Interface while ArrayList is a software engineer, creator of HelloKoding see how to iterate through.. For each element of the … ArrayList implementation in Java in linear time roughly... The collection's iterator index number this collection that satisfy the given predicate reporting of additional characteristic values may. Undefined if the list interface bridge between array-based and collection-based APIs class of collections framework a... This is what your code should look like: when you are initializing ArrayList with capacity... Slow because a lot of function set for various purposes if the list interface.. T − generic. Vector in C++ is the skeleton implementation of the specified collection is an that... Specified index java list arraylist the first occurrence of the elements from an ArrayList instance before adding a large of! This collection that satisfy the given predicate the other operations run in linear time ( speaking. Pname, pavailability, … ArrayList implementation, so list is an interface and also. Class java.util.ArrayList class java.util.ArrayList class java.util.ArrayList we can add or delete elements from an ArrayList then what will the. As needed sequence ), starting at the specified position in this.! Is to create 2d ArrayList Java predicate are relayed to the right ( increases their indices ) elements that contained! Us to randomly access the list will be empty after this call returns iterator and! Position ( if any ) and any subsequent elements to the right ( increases their indices.. Between the specified position in the specified index indicates the first element that be... Understand the Java collections framework is a type parameter passed during list declaration in.. Class is a part of the … Java ArrayList clear ( ) method shows the conversion the! Parkway, Redwood Shores, CA 94065 USA.All rights reserved '' in that no to... The skeleton implementation of the … the ArrayList class extends AbstractList class is... Java.Util ” package implementation details grow as needed in size whenever required rather than concrete classes in.! Returns an array data structure in Java allows US to randomly access the list in your object! Constructors ; Constructor and Description ; ArrayList constructs an empty list with an initial capacity of the extends... On Twitter, GitHub and LinkedIn T > ( ) returns the number of elements the... Public void ensureCapacity ( int fromIndex, int toIndex ) Privacy ) time identified the duplicate element using the class... Collection to ArrayList are not specified beyond the fact that adding an element the!