![]() ![]() ![]() Dynamically allocated data structures in Java (such as Hashtable, HashSet, HashMap,LinkedList, Vector, Stack, ArrayList) are supported in a unified architecture called the Collection Framework, which mandates the common behaviours of all the classes. ![]() Java Collections are predefined set of classes or data structures which can be used to store multiple items in a single unit. So, use list for storing non-unique objects as per insertion order and use set for storing unique objects in random order Java collections framework List is an ordered sequence of elements, however set is distinct list of element which is unordered. List can be inserted in in both forward direction and backward direction using Listiterator while Set can be traversed only in forward direction with the help of iterator When to use But, no new methods are defined inside Set interface, so we have to use Collection interface methods only with Set subclasses. New methods are defined inside List interface. List permits any number of null values in its collection while Set permits only one null value in its collection. All the elements of a Set should be unique if you try to insert the duplicate element in Set it would replace the existing value. List allows duplicates while Set doesn't allow duplicate elements. List is a type of ordered collection that maintains the elements in insertion order while Set is a type of unordered collection so elements are not maintained any order. Similar to the previous section, we can convert a set to list using the Stream as follows: Set set = list.stream().collect(Collectors.List is an ordered sequence of elements whereas Set is a distinct list of elements which is unordered Set set = new HashSet() Īssertions.assertEquals(4, set.size()) 2.3. The Set.addAll(list) adds all of the elements in the specified collection to this set if they’re not already present. Set set = new HashSet(list) Īssertions.assertEquals(4, set.size()) 2.2. Similar to the previous example, we can use the constructor HashSet(collection) to convert to initialize a HashSet with the items from the ArrayList. List list = List.of(1, 2, 3, 3, 3, 5, 5) 2.1. The method set(int index, Element E) updates the element of specified index with the given element E. So the Set size must be 4 in each method. ![]() The list contains 7 items, but only 4 unique items. Let us begin with creating a List instance, and then we will convert it to the Set. We might need to create a HashSet from a specified ArrayList when we want to remove duplicates from the list because sets do not allow duplicate items. Using Streamįirst, convert the Set to Stream, and then collect the Stream elements to List. ArrayList arrayList = new ArrayList() Īssertions.assertEquals(3, arrayList.size()) 1.3. Using List.addAll()Īnother useful method to get a List with Set elements is to create an empty list instance and use its addAll() method to add all the elements of the Set to List. ArrayList arrayList = new ArrayList(set) Īssertions.assertEquals(3, arrayList.size()) 1.2. It will copy all elements from HashSet to the newly created ArrayList. To convert a given Set to a List, we can use the ArrayList constructor and pass HashSet as the constructor argument. We will be using the following Set to List type in different ways. Also, learn to reverse convert List to Set, a useful method to remove duplicate elements from a list. In this Java tutorial, Learn to convert a specified Set to a List. Both collection types are quite different and have their own usecases. List allows duplicate elements, but Set contains only unique elements. List is an index-based ordered collection, and Set is an unordered collection. In Java, List and Set are Collections types to store elements. ![]()
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