Collections In Java Interview Questions
Collections Interview Questions in Java
Collections In Java Interview Questions
In Java interviews, questions about collections commonly test candidates' understanding of various data structures and their usage in programming. Candidates are often asked to discuss different types of collections available in Java, such as List, Set, and Map, and to explain the differences between them. Candidates may also be asked to demonstrate how to iterate over collections, perform common operations like adding or removing elements, and choose the appropriate collection type for specific use cases based on requirements like ordering, uniqueness, or key-value pairs. Additionally, candidates might be asked about the performance and time complexity of different collection operations, as well as common pitfalls when using collections in Java programming.
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1 - What are the main interfaces in the Java Collections Framework?
The main interfaces in the Java Collections Framework include List, Set, Map, Queue, and Deque. These interfaces provide common data structures for storing and managing collections of objects.
2) What is the difference between List and Set?
List is an ordered collection that allows duplicate elements, while Set is an unordered collection that does not allow duplicate elements. List maintains the insertion order of elements, whereas Set does not guarantee any specific order.
3) How does the HashMap work in Java?
HashMap in Java works based on the key value pair concept. It uses hashing to store and retrieve elements quickly. When you provide a key to the HashMap, it calculates the hash code of the key and stores the key value pair at the calculated index in its underlying array.
4) What is the difference between ArrayList and LinkedList?
ArrayList is implemented as a resizable array, which provides fast element access but slower insertion and deletion operations in the middle of the list. On the other hand, LinkedList is implemented as a doubly linked list, which provides fast insertion and deletion in the middle of the list but slower element access.
5) Explain the concept of the Comparable interface in Java.
The Comparable interface in Java is used to define a natural ordering of objects. By implementing the Comparable interface and overriding the compareTo() method, you can specify the default way objects should be ordered when using sorting methods like Collections.sort().
6) What is the purpose of the Iterator interface in Java?
The Iterator interface in Java provides a way to iterate over a collection of objects without exposing the underlying data structure. It allows you to traverse the elements in a collection sequentially and perform operations like removing elements during iteration.
7) How does the HashSet ensure uniqueness of elements?
HashSet in Java ensures uniqueness of elements by internally using a HashMap to store elements as keys with null values. When you add an element to a HashSet, it calculates the hash code of the element and checks if an element with the same hash code already exists. If not, the element is added; otherwise, it avoids duplicate elements.
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