Java in IntelliJ IDEA: Learn by working with Real Code

We do not just write random code and hope for the best. That is how things break. In this lesson, I will show you how to navigate a real Java project inside IntelliJ IDEA. You will learn to hunt down bugs without wasting time. We have a failing test. A cart total that is too low. I will guide you past the "caveman" way of searching. Instead, we will use IntelliJ shortcuts that feel like magic. Specifically, one shortcut to rule them all: Double Shift. By the end of this short video, you will find files instantly, fix the bug, and see your tests turn green. Let's get started.

We have got a bug. Customer records with blank names are slipping through our cart. It makes checkout messy. Order reports look broken. Let's fix it.

In this video, I will show you how to guard your code against invalid inputs. But we are not just writing code today. We are leveling up your IDE. I will guide you through installing JetBrains AI Assistant to supercharge your workflow. You will see how to get instant documentation without leaving your editor. We will also master shortcuts - because your tool should bend to your will, not the other way around.

Ready? Let's dive in.

We have a bug. A fixed coupon for 15 dollars is giving a massive, incorrect discount. Why? Because the code multiplies instead of subtracting.

In this video, I will show you how to hunt down this bug in IntelliJ IDEA. We will run unit tests directly from the IDE to see the exact gap between expectation and reality. Then, we will jump straight into the PricingService code.

I will guide you through fixing it using a simple Java mathematical function: Math.min.

No overcomplications. Just clean, practical debugging that saves your system from bleeding money. Let's make that test turn green.

We have a bug. The coupon discount is stuck at 0.0. Why? Because someone wrote the code but forgot to actually use it.

In this video, I will show you how to hunt down this kind of dead code inside IntelliJ IDEA.

We will look at the IDE's built-in alerts. We will trace where methods are called - and where they are completely ignored. With one keystroke, we can jump to the problem, fix the code, and see our tests pass. Let's clean up this codebase together.

Adding a feature. Not fixing bugs. Sounds easy? It is actually a trap. One small change can break an entire customer flow. In this video, I will show you how to safely add percentage coupon codes. We do not guess. We use Find Usages to map out the entire project first. We find exactly where the code lives. We write the new percentage rules. We keep the old fixed-amount coupons working exactly as they did before. It is clean. It is safe. Let us build it.

We have a new feature request. Free shipping over $200. Simple, right? But wait. Before we write a single line of code, we need to see what is actually happening. Not what we hope is happening. In this video, I will show you how to use breakpoints in IntelliJ IDEA to inspect real values in real time. We will stop the execution. We will look inside the code's brain. And then, we will write the exact condition to make our new feature work perfectly. No guessing. Just clean, confident debugging.

Let's clean up our code. In this video, I will show you how to refactor without breaking a single thing. We will take messy, duplicated discount logic and clean it up. Why? Because duplicated code is a trap. One side changes, the other stays old, and suddenly your system lies to your customers. I will guide you through choosing a single source of truth. We will move the discount calculation to where it actually belongs: the pricing service. Same features. Better code. Let's get to work.

One discount was fine. Then came coupon discounts. Then loyalty discounts. Suddenly, your code is a foggy mess. You are guessing. I hate guessing. In this video, I will show you how to safely rename your variables across your entire codebase using IntelliJ IDEA. No manual search-and-replace. No missed references. Just clean, precise tools like Shift-F6 that do the heavy lifting for you. We will clean up our parameters, fix compiler issues instantly, and make our code speak clearly again. Let's get to work.

Let us build something big today. A new feature: loyalty tiers.

It sounds simple. Silver gets 5% off. Gold gets 10% off. But there is a dangerous trap here.

If we calculate loyalty before the coupon, the numbers shift. If we calculate it after, they shift again. One misplaced line of code, and our total is wrong by a few dollars.

In this lecture, I will guide you through this step-by-step. We will read the existing flow first, pinpoint the exact spot for our logic, and build a clean Java enum. No rushed edits. Just careful, structured progress.

Let us make this codebase solid.

Ever lose your code? We all do. Maybe you deleted a perfect block hours ago. Git was not tracking it. Ctrl-Z cannot help you because you closed the IDE. Do not panic. I have a secret. In this video, I will show you my favorite IntelliJ feature: Local History. It is a built-in time machine. It tracks every change, every edit, and every mistake automatically. We will jump back in time together and rescue your lost code in seconds. Let us dive in.