What are collections in Java and what are they used for?

Collections in Java are a set of interfaces and classes that represent data structures for storing and processing groups of objects. They standardize the ways of representing and working with data, making code more flexible and reusable.

Used for:

• Storing and organizing data: Provide various ways to place objects (lists, sets, maps).
• Efficient data operations: Simplify performing typical operations such as adding, removing, searching, sorting.
• Compatibility: Provide a unified API for working with different types of collections.
• Performance enhancement: Some collection implementations are optimized for specific usage scenarios.

Main collection interfaces:

• Collection: The root interface that defines basic operations (adding, removing, iterating).
• List: An ordered collection with index-based access (can contain duplicates).
• Set: A collection of unique elements without a specific order.
• Map: Stores key-value pairs (keys are unique).

Examples of implementation classes:

• ArrayList, LinkedList (for List)
• HashSet, TreeSet (for Set)
• HashMap, TreeMap (for Map)

Example of using ArrayList:

// Creating a list of strings
List<String> names = new ArrayList<>();
// Adding elements
names.add("Alice");
names.add("Bob");
// Iterating over the list
for (String name : names) {
    System.out.println(name);
}