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Introduction to Collections, Generics & Reflection in Java (Udemy.com)

A Guide to Understand Generics, Collections Framework (Data Structures), Stream API and Reflection in Java!

4.5
3,649 reviews

Created by: Holczer Balazs

Last updated September 2026

Our take

Based on the ratings of 3,649 students, a sample of their written reviews and the syllabus, as the course stood in September 2026. No course pays to be reviewed.

This is a focused Java course, not a start-from-zero class. It spends its first few hours on generics: type parameters, bounded types, wildcards and type erasure. Then it moves to the collections framework (lists, stacks, queues, maps, sets, sorting), a long Stream API block of 21 lectures, and a short reflection section. The syllabus shows about 11 hours across 118 lectures, and it was last refreshed in September 2026. The requirements ask for basic Java, meaning loops and classes.

Reviewers like the teaching style. Holczer Balazs explains the theory first and then shows it in the IDE, and reviewers say that balance makes the concepts easier to follow. One said wildcards, which they used to find confusing, are explained well here. Another called reflection the part that surprised them most. The complaints are small and consistent. Two three-star reviewers wanted an assignment after each concept, and the syllabus backs that up: there are 13 coding exercises and 28 quizzes, but only two homework videos. One one-star review said some code did not work and got no explanation.

With 29,181 students and a 4.5 average from 3,649 reviews, it has a solid track record. Most reviews are short, so there is little detail on pace. It is a good pick if you want to understand why an ArrayList and a LinkedList behave differently, not just how to call them. Pair it with your own small projects or a practice site, since the drills are light. Anyone still learning basic syntax should start elsewhere first.

Best forJava beginners who know classes and loops and want to understand generics, collections and how they work under the hood.
Skip it ifYou want lots of practice problems, or a full Java course from scratch with no prior coding.

Pros

  • Explains theory first, then shows it in the IDE, which reviewers find easy to follow
  • Wildcards and type erasure get real time, and a reviewer says wildcards finally made sense
  • Collections section covers how lists, maps and sets work internally, with running time comparisons
  • Updated September 2026, with 28 quizzes and 13 coding exercises along the way

Cons

  • Reviewers want practice after each concept, but there are only two homework exercises
  • Reflection runs about 36 minutes, so it is a taste rather than full coverage
  • One reviewer hit code that failed with no explanation of the cause
He provides very detailed explanations, which is helpful and makes it easier to understand the concepts on various complexity levels. Also, the balance between theory and coding examples is also great.
Anuj Sharma, a student

Suits Java beginners who already know loops and classes; total newcomers to programming will struggle.

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What you will learn

  • Understand the basics of generics
  • Understand bounded type parameters
  • Understand wildcards (unbounded, upper bounded and lower bounded wildcards)
  • Understand type erasure and type inference
  • Understand the basic data structures
  • Understand hash maps and sets
  • Understand lists (ArrayLists and LinkedLists)
  • Understand stacks and queues
  • Understand the Collection Framework
  • Understand hashing and hash-functions
  • Understand Stream API

Course content

21 sections · 118 lectures · 11 hours of video 28 quizzes, 13 coding exercises, 16 articles

  1. 1Introduction 2 free previews2 lectures · 7 min
  2. 2### GENERICS AND GENERIC PROGRAMMING ### 1 free preview1 lecture · 1 quiz · 7 min
  3. 3Basic Generics 1 free preview6 lectures · 2 quizzes · 29 min
  4. 4Bounded Type Parameters4 lectures · 3 quizzes · 16 min
  5. 5Type Inference4 lectures · 1 quiz · 16 min
  6. 6Wildcards9 lectures · 2 quizzes · 48 min
  7. 7Type Erasure5 lectures · 1 quiz · 20 min
  8. 8Homework Exercise I - Generics1 lecture · 1 quiz · 8 min
  9. 9### COLLECTIONS FRAMEWORK ###3 lectures · 1 quiz · 26 min
  10. 10Lists12 lectures · 3 quizzes · 1 hour

Who it is for

The instructor says it suits

  • Beginner Java developers curious about generics, collections and reflection

What you need before you start

  • Internet connection
  • Basic Java (loops, classes etc.)

How it compares

Against the other 231 rated Udemy courses in Java on CourseDuck:

  • Rating4.5 out of 5higher than 53% of them
  • Reviews3,649#65 of 232 by number of reviews
  • Length11 hourslonger than 57% of them
  • Last updatedSeptember 2026more recently than 94% of them

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Quality Score

Content Quality
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Video Quality
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Qualified Instructor
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Course Depth & Coverage
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Overall Score : 90 / 100

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Course Description

Learn the basic concepts and functions  that you will need to build fully functional programs with the popular programming language, Java.

This course is about generics in the main. You will lern the basics of generic types, generic methods, type parameters and the theoretical background concerning these topics. This is a fundamental part of Java so it is definitly worth learning.

Section 1 - Generic and Generic Programming

  • why to use generics and generic programming

Section 2 - Basic Generics

  • generic types

  • generic methods

  • fundamentals of generics and generic programming

Section 3 - Bounded Type Parameters

  • bounded type parameters

Section 4 - Type Inference

  • what is type inference

Section 5 - Wildcards

  • what are wildcards?

  • lower bounded wildcards

  • upper bounded wildcards

  • wildcards and bounded type parameters

Section 6 - Type Erasure

  • what is type erasure?

  • bridge methods and type erasure

Section 7 - Collections Framework

  • the collections framework

  • measuring the running time of algorithms

  • what are data structures?

Section 8 - Lists

  • ArrayList and LinkedList

  • performance comparison of LinkedLists and ArrayLists

  • Vectors

  • Stacks

Section 9 - Queues

  • what are queues?

  • PriorityQueues

  • ArrayDeques

Section 10 - Maps

  • hashing based data structures and hash-functions

  • HashMaps and LinkedHashMaps

  • balanced binary search trees and red-black trees

  • TreeMaps

Section 11 - Sets

  • what are sets?

  • HashSets, LinkedHashSets and TreeSets

Section 12 - Sorting Collections

  • sorting arrays and collections

  • Comparable and Comparator interfaces

  • sorting with lambda expressions

Section 13 - Stream API

  • streams

  • sequential streams and parallel streams

  • map() and flatMap()

  • reduce()

Section 13 - Reflection

  • what is reflection?

  • annotations and reflection

  • reflection and frameworks (such as Spring)

Learning the fundamentals of Java is a good choice and puts a powerful and tool at your fingertips. Java is easy to learn as well as it has excellent documentation, and is the base for all object-oriented programming languages.

Jobs in Java development are plentiful, and being able to learn Java will give you a strong background to pick up other object-oriented languages such as C++, or C# more easily.
Read More All Levels All Levels product length iconTime: 11h

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Instructor Details

Holczer Balazs

My name is Balazs Holczer. I am from Budapest, Hungary. I am qualified as a physicist. At the moment I am working as a simulation engineer at a multinational company. I have been interested in algorithms and data structures and its implementations especially in Java since university. Later on I got acquainted with machine learning techniques, artificial intelligence, numerical methods and recipes such as solving differential equations, linear algebra, interpolation and extrapolation. These things may prove to be very very important in several fields: software engineering, research and development or investment banking. I have a special addiction to quantitative models such as the Black-Scholes model, or the Merton-model.

Take a look at my website if you are interested in these topics!

Read More

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Reviews

4.5

3,649 ratings on Udemy

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By Satya In on 2/20/2025

The course is great and it provides the In depth underatanding of all the topics. I am impressed how they explained generics in details , as I used to find wildcards in generics little confusing.

By Vishal Vernekar on 5/21/2024

Tells code does not work fine but does not give reason why. What is the issue.

By Anuj Sharma on 12/7/2023

He provides very detailed explanations, which is helpful and makes it easier to understand the concepts on various complexity levels. Also, the balance between theory and coding examples is also great. Highly recommended for beginners!

By Devanshu Kumar on 11/11/2023

The course was awesome for me. In my past, I did not dwell on Collection, Reflextion API so much. In this course, Holczer Balazs taught me crucial information about Collection, Stream API and Reflection. Initially, I was not informed about the magic of Reflection API. This course uncovered lots of the things of Reflection API. Although a deep understanding these topics is must for future growth, people can still get lots of knowledge from this course which could be essential for their projects as well as interviews.

By Anonymized User on 2/20/2023

I really enjoying this course, it gives better insight on collection and it’s internal working. This course was well constructed to understand. I recommended this to my friend.

By Sidnei Junior on 3/16/2022

Awesome course, it exceeded my expecations for sure! The course mix theorics and practices, where if you get a doubt during the theory explanation, in the practical session you will be fine.

By Luis Lugo on 5/18/2021

Sinceramente fue un curso excelente, siempre tenía dudas con el uso de datos genéricos, y gracias a este curso pude resolver esas dudas. Me atrevo a decir que este curso me ayudo mas que los cursos elementales de pluralsight.

By Weronika Sleboda on 1/20/2021

Wow, this is first time when I finished the course on udemy. The best instructor on udemy so far. After each lecture I actually felt that I learnt something. No wasting time, no talking irrelevant nonsense. Just straight to the point, good explanations, practical examples, great teaching skills, nice and clear accent. Thank you! I'm waiting for more java courses from this instructor (already bought plenty). I highly recommend for those who want to learn fast without wasting hours after hours on listening to empty talk.

By Pavel Marchev on 6/29/2016

This course has very well explained information! There could be more explanations and comparisons about the upper and lower -bounded parameters/types, as well as information about synchronization in Map implementations, since the course is about Java basics.

By Rahul Choudhary on 5/26/2016

he has missed lot of things, like detailed explanation on working of hash map, fail safe -- fail -fast iterator, how to make collection read only, and reason why we do that.

By Amir Farah

as the tutor said from the start the resolution is not great, i need to use some magnifier in windows to see the code.
besides that issue , every thing is great.

By Rajeev Kumar Singh

A good way to get started with programming.
The instructor has great clarity of a subject which resulted in better grasp.
Except for video quality below 1080p everything was good. Had a hard time watching them on iPad and mobile due to the video quality.

Showing 12 of 55 reviews

Introduction to Collections, Generics & Reflection in Java
Visit course on Udemy Write a review
  • Video Duration: icon 11h
  • Price: $10.99
  • Provider: icon Udemy
  • Updated: icon September 2026
  • Level: All Levels All Levels
  • Language: icon English
  • Certificate: icon Yes
  • Lectures:118 in 21 sections
  • Practice:28 quizzes, 13 coding exercises
  • Students:29,200
  • Subtitles:5 languages
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