Intro to Java — Data Structures & Algorithms

A hands-on reference repo for anyone learning Java and foundational computer science concepts. Each folder is self-contained and focuses on one topic, making it easy to explore at your own pace.

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Who this is for

• People new to Java who want to see how common data structures are built from scratch
• Anyone learning CS fundamentals alongside a course or textbook
• Developers coming from another language who want to understand how Java handles generics, OOP, and algorithms

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Topics

Folder	What you'll learn
classes/	Java classes, fields, methods, and constructors
absinter/	Abstract classes and interfaces
pai/	Polymorphism — shapes example (Polygon, Rectangle, Triangle)
generics/	Generic data structures: ArrayList, LinkedList, Stack, Queue, HashMap
recursion/	Recursive thinking and common recursive problems
sorting/	Bubble, insertion, selection, merge, quick, and radix sort
trees/	Binary search tree (BST) with insert, search, and delete
graphs/	Graphs with BFS, DFS, and Dijkstra's shortest path
hash/	Hash table with chaining and dynamic resizing
heap/	Generic max-heap with heapifyUp, heapifyDown, and rebuildHeap

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How to run any file

No build system is required — just javac and java.

# Compile (from the repo root)
javac heap/MaxHeap.java heap/MaxHeapTest.java

# Run
java -ea -cp . heap.MaxHeapTest

Replace heap and MaxHeapTest with whichever folder and file you want to run. The -ea flag enables assert statements used in test files.

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Suggested learning order

If you're just starting out, work through the topics roughly in this order:

1. classes/ — understand objects first
2. absinter/ and pai/ — inheritance and polymorphism
3. generics/ — build the core structures (list, stack, queue)
4. recursion/ — essential for understanding trees and sorting
5. sorting/ — classic algorithms
6. trees/ — your first tree structure
7. hash/ — hash tables and collision handling
8. graphs/ — BFS, DFS, weighted graphs
9. heap/ — priority queues and heap operations