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Week 03: Collections & File I/O

Exception handling, reading and writing files, working with dates, ArrayList and HashMap, plus Agile basics and GitHub project boards

Module 1 - File I/O Reading

Runtime errors, exceptions, and how try/catch keeps your program running

BufferedReader Pipeline

Disk file → FileReader → BufferedReader → readLine() loop until null

Module 2 - File I/O Writing & Dates

FileWriter vs BufferedWriter

Direct write vs buffered — when the 8K buffer flushes, append mode

LocalDate / LocalTime / LocalDateTime

Three date types — what each holds and when to use which

DateTimeFormatter Playground

Build a pattern, see the output — parse and format date strings

Module 3 - Collections: Lists

Array vs ArrayList

Fixed size vs dynamic — side-by-side comparison of operations

ArrayList Operations

add, get, set, remove, size — with element-shift animation using Product objects

Module 4 - Collections: Maps

HashMap Hashing & Buckets

Key → hash → bucket → value — why the order isn't insertion order

HashMap Operations & Iteration

put, get, remove, null on miss — values(), keySet(), entrySet()

ArrayList vs HashMap — Pick One

Decision tree: order, fast lookup, index — when each is the right tool

Workbook 3b - Agile Software Development

Waterfall vs Agile

Two approaches side by side — what breaks when requirements change

Sprint loop, daily standup, retrospective, and the three Scrum roles

User Story Anatomy

Write user stories from the user's perspective — and when it's just a technical task

GitHub Project Board Walkthrough

Kanban board in action — Todo, In Progress, QA, Done with drag and details

Quick Reference Guides

Week 3 Cheat Sheet

Quick reference for try/catch, File I/O, Dates, ArrayList, HashMap, and Agile terms

Glossary / Key Terms

All Week 3 vocabulary — Collection, Exception, Stream, Sprint, MVP, User Story, and more

Common Errors Guide

FileNotFound, IOException, NullPointer on HashMap miss, forgotten close() and more

Date Format Patterns

DateTimeFormatter pattern reference — yyyy, MM, dd, HH, mm, ss with examples

Exercise companions help you understand each exercise — what to build, what a successful run looks like, and which concepts you need. No solutions, no spoilers.

Workbook 3a - File Reading

Display a quote by number, then add try/catch so bad input doesn't crash the program

Bedtime Stories

Read a text file line by line with BufferedReader and print it with line numbers

Payroll Calculator (Read)

Read employee data from CSV, build Employee objects, compute gross pay

Workbook 3a - File Writing & Dates

Payroll Calculator (Write)

Write the payroll report to a CSV file — bonus: JSON output

Display the current date and time in four different formats using DateTimeFormatter

Search Engine Logger

Log user actions to a file with timestamps — launch, search, exit

Workbook 3a - Collections

Search Inventory (ArrayList)

Store a product inventory in an ArrayList, load from CSV, display and search

Search Inventory (HashMap)

Same inventory, but keyed by product name for fast lookup

Workbook 3b - Agile

User Stories (Hardware Store)

Turn vague requirements into focused user stories — one per user type

GitHub Project Board

Set up a board for the Hardware Store user stories — columns, cards, details

Workshop 3w

Week 3 workshop — CLI store with product list, cart, and checkout using a provided skeleton

Practice what you learned with interactive games — test your knowledge, race the clock, and have fun.

Exceptions & File I/O

Exception Hunter

Read the code, predict which line throws what exception

Match file operations to the correct reader, writer, or buffer class

Dates

Match pattern strings to example outputs — yyyy, MM, dd, HH and more

Collections

ArrayList Tracer

Predict the ArrayList state after a sequence of add, remove, and set calls

Quick-fire key/value questions — what does get() return?

Collection Picker

Given a scenario, pick the right tool — ArrayList or HashMap?

Agile

User Story Builder

Rearrange the parts to build a valid user story — spot the bad ones

Flashcard quiz — Scrum, Sprint, MVP, Retro, Standup and more

Mixed Review

Find the bug and pick the fix — Week 3 edition covering files, dates, collections

Flashcard Quiz 3

Test your Week 3 vocabulary — exceptions, file I/O, collections, Agile

Capstone

Open for Business

Run an online store — load inventory from file, manage cart, handle errors