What is a collection in Java?

A collection in Java is an object that groups multiple elements into a single unit. It provides a unified and efficient way to store, retrieve, and manipulate groups of objects.

What are the advantages of using collections in Java?

Using collections in Java has several advantages, including:

• Efficient storage and retrieval of data
• Built-in algorithms for sorting and searching data
• Dynamic resizing of data structures
• Simplified and cleaner code for manipulating groups of objects
• Improved code reusability and maintainability

What is the difference between a Collection and an Array in Java?

An array is a fixed-length data structure that stores a group of elements of the same type. A collection, on the other hand, is a dynamic data structure that can grow or shrink as needed and can store elements of different types. Arrays offer fast random access to elements, while collections offer more flexible and efficient ways to manipulate groups of elements.

What is the difference between the Collection and Collections classes in Java?

The Collection class is an interface that defines the basic behavior of a group of objects in Java. The Collections class, on the other hand, is a utility class that provides static methods for working with collections. The Collections class provides methods for sorting, searching, and manipulating collections, as well as for creating unmodifiable or synchronized collections.

What are the main interfaces in the Collection framework?

The main interfaces in the Collection framework include:

• Collection: Defines the basic behavior of a group of objects in Java
• List: An ordered collection of elements that can contain duplicates
• Set: A collection that contains unique elements and does not allow duplicates
• Queue: A collection designed for holding elements prior to processing, allowing elements to be inserted at one end and removed from the other end
• Map: A mapping between keys and values

What is the difference between a List and a Set in Java?

A List is an ordered collection of elements that can contain duplicates, while a Set is an unordered collection that contains unique elements and does not allow duplicates. Lists allow fast sequential access to elements, while Sets provide more efficient ways to check for the presence of elements and to iterate over the collection.

What is the difference between a HashSet and a TreeSet?

A HashSet is an unordered collection that uses hashing to store and retrieve elements, while a TreeSet is an ordered collection that uses a red-black tree to store and retrieve elements. HashSet provides constant-time performance for the basic operations (add, remove, contains), while TreeSet provides log(n) performance for these operations. HashSet allows one null element, while TreeSet does not allow any null elements.

What is the difference between an ArrayList and a LinkedList?

An ArrayList is a dynamic array implementation of the List interface, while a LinkedList is a doubly linked list implementation of the List interface. ArrayList provides constant-time access to elements, while LinkedList provides constant-time insertion and deletion of elements. ArrayList is more efficient when accessing elements, while LinkedList is more efficient when performing insertion and deletion operations.

What is the difference between fail-fast and fail-safe iterators?

Fail-fast iterators are designed to throw a ConcurrentModificationException when a collection is modified while being iterated over. Fail-safe iterators, on the other hand, do not throw an exception and instead operate on a copy of the collection.

What is the difference between a HashMap and a Hashtable?

A HashMap is an unsynchronized implementation of the Map interface, while a Hashtable is a synchronized implementation of the Map interface. HashMap allows one null key and multiple null values, while Hashtable does not allow any null keys or values. HashMap is generally faster than Hashtable, but is not thread-safe.