Builder Pattern Concept Art
construction Creational Design Pattern

The Builder Pattern

Construct complex objects step-by-step. Separate the construction process from the final representation.

psychology_alt The Problem

Imagine a complex object like a Custom PC. It has dozens of parts: CPU, GPU, RAM, storage, cooling, case, lights, etc.

Without a pattern, you might end up with a new PC(intel, nvidia, 32gb, 1tb, ...) constructor with 10+ arguments. What if you don't want lights? What if the cooling is standard? The Builder Pattern solves this by letting you construct the object step-by-step.

The Solution (Fluent Interface)

new PCBuilder()
  .setCPU("i9-14900K")
  .setGPU("RTX 4090")
  .setRAM("64GB")
  .build();

Dream Rig Builder 2025

Interactive Demo
memory

1. Select CPU

Pending
videogame_asset

2. Select GPU

Pending
cases

3. Select Chassis

Pending
director.js
const builder = new PCBuilder();

// Method Chaining
builder
...waiting for selection...
const myRig = builder.build();

Current Spec

Total Estimate
$0
Select components to start building...

check_circle Advantages

  • 1

    Complete Control

    Construct objects step-by-step, defer construction steps, or run steps recursively.

  • 2

    Reusable Code

    Reuse the same construction code when building various representations of products (e.g., Office PC vs Gaming PC).

  • 3

    Single Responsibility

    Isolate complex construction code from the business logic of the product itself.

cancel Disadvantages

  • 1

    Complexity

    The code becomes more verbose since the pattern requires creating multiple new classes (Director, Builder, ConcreteBuilder).

  • 2

    Redundancy

    You often have to duplicate portions of the domain object's fields in the builder class.