Java Generics, Collections, Optionals and Streams
Write cleaner modern Java with type-safe generics, the right collections, null-safe Optional, and powerful Stream pipelines.
Write Java That Looks Like Real Production Code
A lot of Java developers can write loops, lists, and maps. But real production Java expects more than that. You need to understand why Generics make code type-safe, which collection to choose for the job, how Optional prevents null-related bugs, and how Streams let you process data clearly without writing endless loops. This course teaches modern Java through focused, runnable examples. One unit. One concept. One complete example. No giant project to distract you. No vague theory. Just the exact skills you need to write cleaner Java.
By the end, you will understand Generics, Collections, Optional, and Streams well enough to use them in real backend code and explain them in Java interviews. You will not just know the API names — you will know when to use each tool and why it matters.
What you'll actually learn
- Generics from First PrinciplesUnderstand why Generics exist, how to write generic classes and methods, and how bounds and wildcards create flexible, type-safe APIs.
- The Collections FrameworkMaster ArrayList, LinkedList, HashSet, TreeSet, LinkedHashSet, PriorityQueue, ArrayDeque, HashMap, TreeMap, and the trade-offs behind each one.
- Optional and Null SafetyStop returning null and start writing safer APIs with Optional, map, filter, orElse, orElseGet, and orElseThrow.
- Streams and Functional JavaUse filter, map, flatMap, reduce, sorted, min, max, matching operations, and collectors to process data clearly.
- Advanced CollectorsBuild real reporting pipelines using groupingBy, partitioningBy, joining, toMap, counting, summing, and downstream collectors.
- Java Interview PrepPractice explaining Generics, wildcards, PECS, collection trade-offs, Optional, stream laziness, collectors, and performance.
Who should take this course
- ✓ Full course access
- ✓ Run Java in browser
- ✓ Hands-on coding units
- ✓ Interview prep built in
- ✓ Collections & Streams
- ✓ Optional null safety
- ✓ Full Java library
What students say
"I avoided Generics for years because they looked confusing. This course finally made wildcards, bounds, and PECS make sense."
"The Collections section gave me the mental model I was missing. I finally know when to use ArrayList, HashMap, TreeMap, HashSet, and ArrayDeque."
"Streams finally clicked. I went from long loops to clean pipelines that are easier to read and explain."
Course Curriculum
Write reusable, type-safe Java code using generic classes, methods, bounds, and wildcards.
| Unit | Lesson | What You'll Learn |
|---|---|---|
| 1 | Why Generics? The Problem Without Generics | See how Object-based containers cause unsafe casting, runtime ClassCastException, and weak API design |
| 2 | Introduction to Generic Classes | Build a Container<T> class and see how Generics enforce type safety at compile time |
| 3 | Generic Naming Conventions and Multiple Type Parameters | Use T, E, K, V, and build a Pair<K, V> class that carries two independent types |
| 4 | Bounded Types with extends | Restrict generic types with extends and safely call methods from the upper bound |
| 5 | Bounded Types with Interfaces | Use multiple bounds with class and interface constraints to design safer generic APIs |
| 6 | Unbounded Wildcards (?) | Use List<?> and Container<?> when you need flexible read-only access across unknown types |
| 7 | Upper Bounded Wildcards (? extends) | Apply Producer Extends to read safely from collections of subtypes |
| 8 | Lower Bounded Wildcards (? super) | Apply Consumer Super, write into flexible collections, and understand the full PECS principle |
Frequently Asked Questions
Write Cleaner Java With Confidence
Master Generics, Collections, Optional, and Streams through focused examples you can actually use.