The Java Collections Framework is a collection of interfaces and classes which helps in storing and processing the data efficiently. This framework has several. This java article contains differences between Collection and Collections in java, How Collection interface difffers from Collections class. Also shared the tricky coding interview questions in our previous posts. Today, we will learn about the top 50 java collections interview questions and answers.
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The Collection in Java is a framework that provides an architecture to store and manipulate the group of objects. Java Collection framework provides many interfaces (Set, List, Queue, Deque) and classes (ArrayList, Vector, LinkedList, PriorityQueue, HashSet, LinkedHashSet, TreeSet. In Java, collection interview questions are most asked by the interviewers. Here is the list of the most asked collections interview questions with answers. OOP: Collections. 1. Collections in Java. • Arrays. ▫ Has special language support. • Iterators. ▫ Iterator (i). • Collections (also called containers). ▫ Collection (i).
The SortedSet provides the additional methods that inhibit the natural ordering of the elements. Root interface in collection hierarchy is Collection interface. What is Collection framework The Collection framework represents a unified architecture for storing and manipulating a group of objects. I guess in HashMap only null keys are supported and not null values.. It will be very helpful to have an image of the main collections collection, set, list, Queue and map sometimes is easier to watch the image as a tree than reading the description. What is Comparable and Comparator interface? HI, Great work done for collating all questions at one place.
Thanks, Karan. Vaibhav Prajapati November 24, It is very useful tutorial to understand the collection concept…. Saurabh Kumar January 7, 6: Leandro Severino January 8, Manoj November 29, 7: Jagan December 7, 3: Laxman December 15, 8: Ramya March 1, 7: Deepchand chauhan April 7, 5: Sevinc March 12, 8: It was very useful to understand the concept clearly.
Let us see the hierarchy of Collection framework. The java. The Iterable interface is the root interface for all the collection classes. The Collection interface extends the Iterable interface and therefore all the subclasses of Collection interface also implement the Iterable interface. The Collection interface is the interface which is implemented by all the classes in the collection framework.
It declares the methods that every collection will have. In other words, we can say that the Collection interface builds the foundation on which the collection framework depends. Some of the methods of Collection interface are Boolean add Object obj , Boolean addAll Collection c , void clear , etc.
List interface is the child interface of Collection interface. It inhibits a list type data structure in which we can store the ordered collection of objects. It can have duplicate values. There are various methods in List interface that can be used to insert, delete, and access the elements from the list. The ArrayList class implements the List interface. It uses a dynamic array to store the duplicate element of different data types.
The ArrayList class maintains the insertion order and is non-synchronized. The elements stored in the ArrayList class can be randomly accessed.
Consider the following example. LinkedList implements the Collection interface. It uses a doubly linked list internally to store the elements. It can store the duplicate elements. It maintains the insertion order and is not synchronized. In LinkedList, the manipulation is fast because no shifting is required. Vector uses a dynamic array to store the data elements. It is similar to ArrayList.
However, It is synchronized and contains many methods that are not the part of Collection framework. The stack is the subclass of Vector. It implements the last-in-first-out data structure, i. The stack contains all of the methods of Vector class and also provides its methods like boolean push , boolean peek , boolean push object o , which defines its properties.
Queue interface maintains the first-in-first-out order. It can be defined as an ordered list that is used to hold the elements which are about to be processed. The PriorityQueue class implements the Queue interface. It holds the elements or objects which are to be processed by their priorities.
PriorityQueue doesn't allow null values to be stored in the queue. Deque interface extends the Queue interface. In Deque, we can remove and add the elements from both the side. Deque stands for a double-ended queue which enables us to perform the operations at both the ends. ArrayDeque class implements the Deque interface. It facilitates us to use the Deque.
Unlike queue, we can add or delete the elements from both the ends. Set Interface in Java is present in java. It extends the Collection interface.
It represents the unordered set of elements which doesn't allow us to store the duplicate items. We can store at most one null value in Set. HashSet class implements Set Interface.
It represents the collection that uses a hash table for storage. Hashing is used to store the elements in the HashSet. It contains unique items. It extends the HashSet class and implements Set interface.