The Java Collections Framework is essential for every Java developer. Here’s a comprehensive guide.

Collection Hierarchy

Collection
├── List
│   ├── ArrayList
│   ├── LinkedList
│   └── Vector
├── Set
│   ├── HashSet
│   ├── LinkedHashSet
│   └── TreeSet
└── Queue
    ├── PriorityQueue
    └── Deque
        └── ArrayDeque

Lists

ArrayList

List<String> list = new ArrayList<>();
list.add("Java");
list.add("Python");
list.get(0); // "Java"
list.remove(0);

LinkedList

List<String> list = new LinkedList<>();
list.add("First");
list.add("Last");
// Better for frequent insertions/deletions

Sets

HashSet

Set<String> set = new HashSet<>();
set.add("Java");
set.add("Java"); // Duplicate ignored
set.contains("Java"); // true

TreeSet

Set<String> set = new TreeSet<>();
set.add("Zebra");
set.add("Apple");
// Automatically sorted: [Apple, Zebra]

Maps

Map<String, Integer> map = new HashMap<>();
map.put("Java", 1);
map.put("Python", 2);
map.get("Java"); // 1
map.containsKey("Java"); // true

Best Practices

  1. Use ArrayList for random access
  2. Use LinkedList for frequent insertions
  3. Use HashSet for unique elements
  4. Use TreeSet for sorted unique elements
  5. Use HashMap for key-value pairs

Conclusion

Master Java Collections to write efficient code! 📚