What is the Facade pattern?

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creational

Facade

Provide a simplified, unified interface to a complex subsystem.

Some subsystems are powerful but awkward. Video conversion is a good example: decoders, buffers, codecs and mixers, all of which must be used in the right order.

If every caller has to learn that sequence, two things go wrong. The same setup code gets copied around the project. And when the subsystem changes, every one of those copies breaks.

Facade adds one simple entry point that handles the common case. Callers ask for what they want, such as convert(file, format), and the facade deals with the machinery.

What the interviewer is probing.

1. "What does a Facade give you?" *Probing:* the purpose. *Stalls:* "Simplicity." *Moves up:* one simple entry point to a complex subsystem, so callers are not coupled to its internal classes and ordering.

2. "Does it prevent access to the subsystem?" *Probing:* the precision. *Stalls:* "Yes." *Moves up:* no — it is a convenience, not a restriction; advanced callers can still use the subsystem directly.

3. "When does a facade become a problem?" *Probing:* the judgement. *Stalls:* "Never." *Moves up:* when it grows into a god object that every feature adds to, which is a sign the subsystem needs splitting instead.

4. "How does it relate to a service layer?" *Probing:* the practical connection. *Stalls:* "Not at all." *Moves up:* an application service is usually a facade over domain and infrastructure, which is why the pattern appears without being named.

A hotel concierge — you ask to book a restaurant and taxi. The concierge handles the coordination.

Key Concepts

The facade offers a few methods named after what the caller wants to achieve, not after the steps involved.

Inside, it creates the subsystem objects and calls them in the correct order. That knowledge now lives in one place instead of being spread across the codebase.

The subsystem stays public. Anyone who needs fine control can still use it directly. The facade is a convenience, not a wall.

It also gives you room to move. As long as the facade's methods keep working the same way, you can rewrite everything behind it.

java

public class VideoConverter {
    public File convert(String filename, String format) {
        VideoFile file = new VideoFile(filename);
        Codec codec = new CodecFactory().getCodec(format);
        Buffer buffer = new BitrateReader().read(file, codec);
        AudioTrack audio = new AudioMixer().mix(file.getAudioTracks());
        return new Encoder().encode(buffer, audio, format);
    }
}
// Client: one simple call
File mp4 = new VideoConverter().convert("birthday.ogg", "mp4");