ArrayList in Java Explained Simply | Internal Working + Big-O | Java Collections Part 4
What is ArrayList in Java? 🤔
If you understand that ArrayList is a dynamic array, the rest becomes much easier.
In this beginner-friendly video, we visually understand how ArrayList works internally — including adding, removing, accessing elements, shifting, resizing, and Big-O complexity.
📚 In this video you'll learn:
✅ What is ArrayList?
✅ ArrayList as a dynamic array
✅ Internal array and capacity
✅ Capacity growth — roughly 1.5×
✅ Adding elements at the end
✅ Amortized O(1) for adding at the end
✅ Adding elements in the middle
✅ Why elements shift to the right
✅ get(index) and direct access
✅ Why get() is O(1)
✅ Removing elements from the middle
✅ Why elements shift to the left
✅ Removing from the end
✅ ArrayList resizing
✅ Creating a bigger array and copying elements
✅ Why resizing is O(n)
✅ ArrayList Big-O explained with the reason, not just memorization
🧠 Remember the picture:
GET → Direct Access → O(1)
ADD at End → Amortized O(1)
ADD in Middle → Shift Right → O(n)
REMOVE in Middle → Shift Left → O(n)
REMOVE at End → O(1)
RESIZE → Copy → O(n)
🎯 The main idea
Don't just memorize Big-O.
Understand what happens to the elements.
If nothing needs to move → think O(1).
If many elements need to move → think O(n).
If ArrayList resizes → elements are copied → O(n).
🎯 Java Collections Made Easy Series
Part 1: Why Do We Need Java Collections?
Part 2: Collection vs Collections
Part 3: List vs Set vs Map vs Queue
Part 4: ArrayList
Part 5: ArrayList vs Array
Part 6: LinkedList
Part 7: ArrayList vs LinkedList
Part 8: What Is a Set?
Part 9: HashSet
Part 10: HashSet Internals
Part 11: LinkedHashSet
Part 12: TreeSet
Part 13: HashSet vs LinkedHashSet vs TreeSet
Part 14: What Is a Map?
Part 15: HashMap
Part 16: HashMap Internal Working
Part 17: HashMap Collision
Part 18: HashMap equals() & hashCode()
Part 19: HashMap Load Factor & Capacity
Part 20: HashMap Resize & Rehashing
Part 21: HashMap Treeification
Part 22: LinkedHashMap
Part 23: TreeMap
Part 24: HashMap vs LinkedHashMap vs TreeMap
Part 25: What Is a Queue?
Part 26: PriorityQueue
Part 27: ArrayDeque & Deque
Part 28: Comparable vs Comparator
Part 29: Iterator & ListIterator
Part 30: Fail-Fast Iterator
Part 31: ConcurrentModificationException
Part 32: Spliterator
Part 33: Collections Utility Methods
Part 34: Immutable Collections
Part 35: Generics with Collections
Part 36: Wildcards & PECS
Part 37: Collections + Stream API
Part 38: Concurrent Collections
Part 39: ConcurrentHashMap
Part 40: BlockingQueue
Part 41: CopyOnWriteArrayList
Part 42: Collection Performance & Big-O
Part 43: Choosing the Right Collection
Part 44: Real-World Collection Problems
Part 45: Java Collections Interview Questions
Part 46: Java Collections Master Revision
🚀 Edutent — Learn. Understand. Grow.
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