![]() ![]() Vector is a synchronized counterpart of ArrayList. ArrayList is more general-purpose and provides random access with index, while LinkedList is more suitable for frequently adding and removing elements from List. Useful implementationsThe most popular implementations of the List interface in Java are ArrayList, LinkedList, and Vector class. In this Java article, we will see the difference between Map, Set, and List in Java and learn when to use List, Set, or Map.Ĥ. ArrayList and LinkedList are the two most popular used List implementations while LinkedHashSet, TreeSet, and HashSet are frequently used Set implementations. Set doesn't allow duplicates, while Map provides a data structure based on key-value pair and hashing.Īll three List, Set, and Map are interfaces in Java and there are many concrete implementations of them are available in Collection API. The Set interface provides an unordered collection of unique objects, i.e. List in Java provides ordered and indexed collection which may contain duplicates. In order to decide when to use List, Set or Map, you need to know what are these interfaces and what functionality they provide. Clearly, the interviewer is looking to know that whether you are familiar with the fundamentals of the Java collection framework or not. ![]() Sometimes this question is asked as When to use List, Set and Map in Java. Similar to the previous section, we can convert a set to list using the Stream as follows: Set set = list.stream().collect(Collectors.Set, List and Map are three important interfaces of the Java collection framework, and the difference between Set, List, and Map in Java is one of the most frequently asked Java Collection interview questions. 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. 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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