The Java Collections Framework is a powerful set of classes and interfaces in the java.util package that provides standard ways to handle groups of objects. It includes data structures such as List, Set, and Map, along with utility classes and algorithms to manipulate them efficiently.
Core Interfaces:
- Collection: Root interface for most collection classes.
- List: An ordered collection allowing duplicates (e.g.,
ArrayList, LinkedList). - Set: A collection that doesn't allow duplicates (e.g.,
HashSet, TreeSet). - Map: A collection that maps keys to values (e.g.,
HashMap, TreeMap).
Common Implementations:
- ArrayList: Fast random access, slow insert/delete in middle.
- LinkedList: Good for insertions/deletions, slower random access.
- HashSet: Fast operations, no order guarantee.
- TreeSet: Sorted elements with log(n) time complexity.
- HashMap: Fast key-value pair access with no ordering.
- TreeMap: Sorted key-value pairs based on keys.
Utilities and Features:
- Collections class: Provides static methods like
sort(), reverse(), shuffle(), and more. - Generics: Used for type safety (e.g.,
List<String> ensures only strings can be added). - Iterators: Used to traverse collections. Methods include
hasNext(), next(), and remove(). - Concurrency support: Thread-safe variants like
Collections.synchronizedList() and concurrent collections like ConcurrentHashMap. - Autoboxing: Automatically converts primitives to wrapper classes for use in collections (e.g.,
int to Integer).
Java Example:
java
import java.util.*;
public class Main {
public static void main(String[] args) {
// Creating a List
List<String> list = new ArrayList<>();
// Adding elements
list.add("Java");
list.add("Python");
list.add("C++");
// Iterating through the list
for (String lang : list) {
System.out.println(lang);
}
}
}
Output:
mathematica
Java
Python
C++
Summary:
Java Collections Framework offers a flexible, efficient, and extensible architecture to work with different types of data structures. Whether you're dealing with dynamic arrays, sets of unique items, or key-value pairs, the framework provides the tools to manage them effectively with minimal effort.