Builder Pattern¶

Intent¶

The Builder Pattern constructs a complex object step by step, separating construction from representation.

Why Was This Pattern Introduced?¶

Imagine creating a Computer object.

computer = Computer(cpu, ram, gpu, storage, os, wifi, bluetooth)

As optional fields increase, constructors become unreadable.

Builder solves this by constructing objects incrementally.

Real-World Analogy¶

Ordering a burger.

You choose bun, patty, cheese, sauces, and toppings one by one.

The final burger is assembled after all choices are made.

Software Engineering Example¶

Building:

HTTP Requests
SQL Queries
Docker Images
Computer Configurations

Python Implementation¶

class Computer:

    def __init__(self):
        self.cpu = None
        self.ram = None
        self.storage = None

class ComputerBuilder:

    def __init__(self):
        self.computer = Computer()

    def add_cpu(self, cpu):
        self.computer.cpu = cpu
        return self

    def add_ram(self, ram):
        self.computer.ram = ram
        return self

    def build(self):
        return self.computer

computer = (ComputerBuilder()
            .add_cpu("Intel i9")
            .add_ram("32GB")
            .build())

How It Works Internally¶

Builder
  ↓
Configure Step-by-Step
  ↓
build()
  ↓
Final Object

Advantages¶

Avoids telescoping constructors.
Readable object construction.
Supports immutable objects.

Disadvantages¶

Additional builder class.
Overkill for simple objects.

When Should You Use It?¶

Many optional fields.
Complex construction process.
Immutable objects.

When Should You Avoid It?¶

Simple objects with few fields.

Common Interview Questions¶

Basic¶

Why Builder over constructors?

Intermediate¶

Difference between Builder and Factory?

Advanced¶

Fluent Builder vs Director?

Pattern	Difference
Factory Method	Chooses which object to create.
Prototype	Clones an existing object.

Key Takeaways¶

Builds complex objects step by step.
Improves readability.
Separates construction from representation.