Learn · Backend & APIs
.NET — where C# runs
If C# is the language, .NET is the engine and toolbox it runs on. Same relationship as Java (the language) to the JVM + its libraries. Knowing this makes “C#/.NET” job posts make sense.
Before we start
- What .NET is (vs the C# language)
- The pieces: runtime, libraries, package manager
- ASP.NET Core — the C# equivalent of Spring Boot
- How the Java world maps to the .NET world
- Explain the difference between C# and .NET
- Name what you’d use to build a .NET web API
- Translate Java tools to their .NET equivalents
Why you’re learning it: “C#/.NET” is one phrase in job posts, and it’s Siemens’ other main stack. Once you see .NET is “Java’s ecosystem with different names,” it stops being scary. Do C# and APIs first. ⏱️ ~20 min.
C# vs .NET — the one confusion, cleared
C# is the language you write. .NET is the platform that runs it: a runtime that executes your code, a giant library of built-in tools, and frameworks for building real apps. You can’t run C# without .NET, just like you can’t run Java without the JVM.
The whole stack maps one-to-one onto the Java world you already know:
You write at the top; the runtime at the bottom executes it. Same shape, different names.
The pieces
- CLR (runtime) — executes your compiled C#. The .NET equivalent of the JVM.
- Base Class Library — collections, files, networking, dates… built in, like Java’s standard library.
- NuGet — the package manager for pulling in libraries. Java’s Maven/Gradle.
- ASP.NET Core — the framework for building web APIs and sites. This is the C# Spring Boot — controllers, routing, dependency injection, all the same ideas from your APIs lesson.
- Entity Framework — the ORM that maps objects to database rows. Java’s JPA/Hibernate.
Modern .NET (formerly “.NET Core”) is cross-platform — it runs on Windows, Linux and Mac, not just Windows anymore.
Java world → .NET world
| Java | .NET |
|---|---|
| JVM (runs your code) | CLR — Common Language Runtime |
| JDK / standard library | Base Class Library (BCL) |
| Maven / Gradle | NuGet (package manager) |
| Spring Boot (web APIs) | ASP.NET Core |
| JPA / Hibernate (ORM) | Entity Framework |
| .jar file | .dll file |
See it? Every Java tool has a .NET twin. You already understand the concepts — you’re just learning new names.
Where you’ll use it — real life
ASP.NET Core builds REST APIs — the same job as Spring Boot, in the C# world.
Banks, healthcare (Siemens), and large firms run heavily on .NET backends.
Entity Framework talks to databases the way JPA does — the SQL you learned still applies.
.NET runs great on Azure (Microsoft’s cloud) and Linux containers.
Now YOU do the reps
- Draw the Java→.NET map from memory: JVM→?, Maven→?, Spring Boot→?, Hibernate→?
- Skim the ASP.NET Core Web API tutorial — notice how much looks like Spring.
Out loud: “What’s the difference between C# and .NET, and what would I use to build a web API in .NET?” Then log it in your Journal.
Back to your Siemens roadmap →