Java Collections

What you will learn

1. 4.1Generics

   Write type-safe, reusable Java code with generic classes and methods, bounded types and wildcards, and understand the limits that type erasure brings.

   1. Why generics?30 min
   2. Write a generic class35 min
   3. Generic methods35 min
   4. Bounded types: <T extends …>40 min
   5. Wildcards: ?, ? extends, ? super40 min
   6. Type erasure and generic limits40 min
   7. Common mistakes and practice40 min

2. 4.2The Collections Framework

   Why collections replace arrays for changing data, how the Collection and Map family tree fits together, and how to pick the right collection for a job.

   1. Why collections, not arrays?25 min
   2. The collection family tree30 min
   3. Choosing the right collection30 min
   4. Common mistakes and practice40 min

3. 4.3Lists

   Store, loop through, search, sort and share ordered data with ArrayList, LinkedList and unmodifiable lists, and understand the cost of each operation.

   1. ArrayList: add, get, set, remove35 min
   2. Looping through a list35 min
   3. Search and sort a list35 min
   4. Lists of your own objects40 min
   5. How ArrayList works inside35 min
   6. LinkedList and when to use it35 min
   7. Fixed and unmodifiable lists35 min
   8. Common mistakes and practice40 min

4. 4.4Sorting & Comparing

   Give your own classes a natural order with Comparable, sort any data in any order with Comparator, and avoid the bugs that make sorts silently wrong.

   1. Natural order with Comparable35 min
   2. Custom order with Comparator35 min
   3. Sorting real data40 min
   4. Common mistakes and practice40 min

5. 4.5Sets

   Store unique values with HashSet, LinkedHashSet and TreeSet, make your own classes work in sets, and combine sets with union, intersection and difference.

   1. HashSet: no duplicates30 min
   2. Sets of your own objects35 min
   3. LinkedHashSet and TreeSet40 min
   4. Union, intersection and difference35 min
   5. Common mistakes and practice40 min

6. 4.6Maps

   Store, look up, count and group data by key with HashMap, LinkedHashMap and TreeMap, and understand how HashMap works inside.

   1. HashMap: keys and values35 min
   2. Looping through a map35 min
   3. Counting and grouping with maps40 min
   4. How HashMap works inside40 min
   5. LinkedHashMap and TreeMap40 min
   6. Maps with your own objects40 min
   7. Common mistakes and practice40 min

7. 4.7Queues, Stacks & Priority Queues

   Handle waiting work in the right order with queues (first in, first out), stacks (last in, first out), deques (both ends) and priority queues (most important first).

   1. Queues: first in, first out35 min
   2. Stacks with ArrayDeque40 min
   3. Deque: both ends40 min
   4. PriorityQueue: always the smallest first40 min
   5. Common mistakes and practice45 min

8. 4.8Utilities & Best Practices

   Brings the section together: the Collections and Arrays helpers, the equals/hashCode rules every collection depends on, choosing by performance, and interview-level review.

   1. The Collections utility class35 min
   2. Moving between arrays and collections35 min
   3. equals and hashCode in collections40 min
   4. Performance and choosing well40 min
   5. Collections interview questions and practice40 min

9. 4.9Collections Mini Projects

   Five console projects that put lists, sets, maps, queues and sorting to work, ending with a library system built entirely on collections.

   1. Student Gradebook60 min
   2. Word Frequency Analyzer60 min
   3. Contact Book60 min
   4. Task Scheduler70 min
   5. Library System with Collections90 min