---
# System prepended metadata

title: Builder pattern

---

# Builder pattern


## Problem

To build a simple house, you need to construct four walls and a floor, install a door, fit a pair of windows, and build a roof. 

But what if you want a bigger, brighter house, with a backyard and other goodies (like a heating system, plumbing, and electrical wiring)?

### extend the base House class
![](https://i.imgur.com/pU7VR3g.png)
you’ll end up with a considerable number of subclasses.

## another approach
![](https://i.imgur.com/1t2I7YY.png)
In most cases most of the parameters will be unused, making the constructor calls pretty ugly.


## Solution: Builder pattern

![](https://i.imgur.com/5A5aXHv.png)

```
builder.buildWalls()
builder.buildDoors()
builder.buildWindows()
builder.buildRoof()

# Add garage
builder.buildGarage()

house = builder.getResult()
```

## when you need to build various representations of the product

![](https://i.imgur.com/Ekefstc.png)


## Director

![](https://i.imgur.com/qHGxXgb.png)

Director: defines the order in which to execute the building steps
Builder: provides the implementation for those steps.

(Having a director class in your program isn’t strictly necessary)

![](https://i.imgur.com/OIntOcF.png)


## Pseudocode

![](https://i.imgur.com/zMLuMq5.png)


## Applicability

1. Use the Builder pattern to get rid of a “telescoping constructor”.
![](https://i.imgur.com/ZSwlY1W.png)


2. Use the Builder pattern when you want your code to be able to create different representations of some product (for example, stone and wooden houses).
![](https://i.imgur.com/EOZH3cU.png)


3. Use the Builder to construct Composite trees or other complex objects.
![](https://i.imgur.com/l4fgUBa.png)


## Builder vs Abstract Factory

![](https://i.imgur.com/qptU7Jv.png)
![](https://i.imgur.com/dX7sC9c.png)