Java Collections provide a flexible way to store, retrieve, and manipulate groups of objects. This guide covers the core collection frameworks and their practical uses.

📋 Key Concepts

  • Collections Framework: A unified architecture for storing and manipulating data (e.g., List, Set, Map)
  • Common Interfaces: Collection, List, Set, Map, Queue
  • Implementations:
    • ArrayList (dynamic array)
    • LinkedList (doubly-linked list)
    • HashSet (hash table)
    • TreeSet (sorted set)
    • HashMap (hash table)
    • TreeMap (sorted map)

📌 Choosing the Right Collection

Use Case Recommended Type 📎 Read More
Ordered, duplicates allowed ArrayList
Fast insertions/deletions LinkedList
Unique elements HashSet
Sorted elements TreeSet
Key-value pairs HashMap
Sorted key-value pairs TreeMap

🧠 Practical Examples

// List example
List<String> fruits = new ArrayList<>(Arrays.asList("Apple", "Banana"));

// Set example
Set<Integer> primes = new HashSet<>(Arrays.asList(2, 3, 5, 7));

// Map example
Map<String, Integer> scores = new HashMap<>();
scores.put("Alice", 95);
scores.put("Bob", 88);

🖼️ Visuals

java_collections_structure
*Understanding the hierarchy of Java collections*
ArrayList_vs_LinkedList
*Performance comparison between ArrayList and LinkedList*

🛠️ Tips

  • Use Collections.sort() for sorting lists
  • Prefer Iterator over for loops for safe modification
  • Leverage Java.util.Collections for utility methods

For advanced topics like thread safety or custom collections, check out our Java Collections Deep Dive.