¶06 - Code Execution
Design it. Write it. Run it.
A UML diagram is a plan. Code is the proof. LLDCanvas lets you implement the class you just diagrammed and execute it in 12 languages - right inside the same workspace, no tab switching, no local setup.
12
languages supported
1
unified workspace
<5s
typical run time
0
local setup required
§01 - Supported runtimes
12 languages. Use the one your interviewer expects.
Every major interview language runs in a real sandboxed environment - not emulated, not transpiled in the browser, not fake.
§02 - The workflow
From UML diagram to running code, without leaving the tab.
// step 01 of 03
Step 01
Design in the UML canvas
Use the drag-and-drop editor or Draft Notation to build your class diagram - classes, methods, relationships, and design patterns.
class diagram
- levels: Level[]
- capacity: int
+ getAvailableSpot()
+ parkVehicle(v: Vehicle)
// step 02 of 03
Step 02
Pick your language, open the panel
Click "Write Code" in the toolbar. A sliding panel appears beside your diagram. Select any of the 12 supported languages.
def __init__(self, levels):
self.levels = levels
def get_available_spot(self):
// step 03 of 03
Step 03
Implement the classes, run it
Write the implementation, add test input, click Run. See real stdout and stderr - no local setup, no tab switching, no waiting.
Spot A-101 is available
Vehicle parked successfully
────────────────────────────────
Process finished · exit code 0
Elapsed: 0.34s
§03 - Why it matters for LLD preparation
The gap between design and implementation is where most candidates get tripped up.
Drawing a UML class diagram is one skill. Writing an actual working implementation from that diagram is another. Both are tested in LLD rounds at companies like Google, Amazon, Flipkart, and Paytm - some interviewers explicitly ask you to implement one or two of the core classes on screen.
Practicing with code execution next to your diagram builds both skills simultaneously. You notice when your design has a gap - when a method signature you drew doesn't make sense to implement, or when a dependency creates a circular import. The feedback loop is immediate.
Combine code execution with the 110+ practice problems and Interview Mode for complete end-to-end practice.
§04 - Panel features
Everything a code panel needs. Nothing it doesn't.
Real stdout and stderr
Get actual compiler/interpreter output - error messages, stack traces, print statements - exactly as you'd see locally.
Stdin support
Paste custom input that your program reads from stdin. Test different inputs without modifying your code.
Draggable panel layout
The code panel and input/output areas are both resizable - drag to give your code or output more space.
Language-aware editor
Syntax highlighting and basic auto-indentation for every supported language in the editor panel.
FAQ
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