Chapter VI

Data Structures in Java

A guided tour of the workhorses of the Java Collections Framework. Each page explains the shape of the structure, its complexity, and a small runnable program you can experiment with.

§ 6.01

Arrays and ArrayList — the workhorses

Fixed-size arrays vs dynamic ArrayList. Memory layout, amortized O(1) append, and when each one shines.

22 min § 6.02

LinkedList and the Deque interface

Doubly-linked nodes, O(1) insert at either end, and why LinkedList is almost never the right choice.

20 min § 6.03

Stacks, queues, and ArrayDeque

LIFO, FIFO, and why java.util.Stack is a historical mistake you should avoid.

24 min § 6.04

HashMap, equals, and hashCode

How hashing works, why you must override equals and hashCode together, and the load factor that keeps lookups O(1).

28 min § 6.05

TreeMap, TreeSet, and ordered structures

Red-black trees under the hood. O(log n) sorted access, range queries, and floor/ceiling lookups.

26 min § 6.06

PriorityQueue — heaps in disguise

Binary heaps, O(log n) insert and extract-min, and the canonical k-largest pattern.

22 min § 6.07

Graphs — adjacency lists and BFS

Modeling graphs in plain Java with Map<Node, List<Node>>, then walking them breadth-first.

30 min

Practice

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