Topic Note: Collections Framework

Course: Java Programming Masterclass - Tim Buchalka (Udemy)
Status: In Progress

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Learning Objectives

• Master the Collections hierarchy
• Choose the right collection for each use case
• Understand internal implementations
• Apply collections efficiently in real-world scenarios

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Key Concepts from the Course

Collections Hierarchy Overview

                    Iterable
                       │
                   Collection
                       │
          ┌────────────┼────────────┐
         List         Set         Queue
          │            │            │
    ┌─────┼─────┐  ┌───┼───┐   ┌────┼────┐
ArrayList  │  LinkedList │  │   │     │
       LinkedList  HashSet │  TreeSet  │
                         │       PriorityQueue
                   LinkedHashSet      ArrayDeque

                      Map (separate hierarchy)
                       │
          ┌────────────┼────────────┐
       HashMap    LinkedHashMap   TreeMap
          │
    ConcurrentHashMap

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List Interface

ArrayList

Characteristics: - Backed by resizable array - O(1) random access - O(n) insertion/deletion in middle - Good default choice for lists

LinkedList

Characteristics: - Doubly-linked list - O(n) random access - O(1) insertion/deletion at known position - Implements both List and Deque

ArrayList vs LinkedList

Operation	ArrayList	LinkedList
get(index)	O(1)	O(n)
add(end)	O(1)*	O(1)
add(index)	O(n)	O(n)**
remove(index)	O(n)	O(n)**
Iterator.remove()	O(n)	O(1)

*amortized, **finding position is O(n), operation is O(1)

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Set Interface

HashSet

LinkedHashSet

TreeSet

Choosing the Right Set

Set Type	Ordering	Null	Performance
HashSet	None	Yes	O(1)
LinkedHashSet	Insertion	Yes	O(1)
TreeSet	Sorted	No*	O(log n)

*TreeSet allows null only if using a Comparator that handles it

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Map Interface

HashMap

Internal Structure: - Array of buckets - Hash function determines bucket - Collision resolution: linked list → Red-Black tree (Java 8+)

Key Operations: - Load factor (default 0.75) - Rehashing when threshold exceeded

LinkedHashMap

TreeMap

ConcurrentHashMap

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Queue & Deque

PriorityQueue

ArrayDeque

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Special Collections

Collections Utility Class

Collections.sort(list);
Collections.reverse(list);
Collections.shuffle(list);
Collections.binarySearch(sortedList, key);
Collections.unmodifiableList(list);
Collections.synchronizedList(list);

Immutable Collections (Java 9+)

List.of(1, 2, 3);
Set.of("a", "b", "c");
Map.of("key1", "val1", "key2", "val2");

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Observed Ideas & Insights

Performance Patterns

Memory Considerations

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Code Snippets & Examples

// Add your practice code snippets here

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Questions to Explore

• How does HashMap handle hash collisions?
• When does HashMap convert buckets to trees?
• What's the difference between fail-fast and fail-safe iterators?

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Quick Reference

Collection	Best For
ArrayList	Random access, iteration
LinkedList	Frequent insert/delete at ends
HashSet	Fast uniqueness check
TreeSet	Sorted unique elements
HashMap	Key-value storage
TreeMap	Sorted key-value pairs
PriorityQueue	Priority-based processing

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