# Refactoring 003 - Extract Constant

> TL;DR: Name all your magic numbers

# Problems Addressed

- Readability

- Complexity

- Code Reuse

# Related Code Smells

- %[https://maximilianocontieri.com/code-smell-02-constants-and-magic-numbers]

# Steps

1. Move the constant code fragment to a constant declaration

2. Replace the values with a reference to the constant.

# Sample Code

## Before

[Gist Url]: # (https://gist.github.com/mcsee/4beca4e8726130c29a74b956df6aefe2)
```java
double energy(double mass) {
  return mass * 300.000 ^ 2;
}
```

## After

[Gist Url]: # (https://gist.github.com/mcsee/17728639113169878b08a95a373624e3)
```java
  // 1. Move the constant code fragment to a constant declaration
final double LIGHT_SPEED = 300.000;

double energy(double mass) {
  // 2. Replace the old code with a reference to the constant.
  return mass * LIGHT_SPEED ^ 2;
}
```

# Type

[X] Automatic
 
Many IDEs support this safe refactoring

# Why code is better?

Constant names add meaning to our code.

Magic numbers are difficult to understand and change.

Code must be as declarative as possible.

# Tags

- Readability

# Related Refactorings

%[https://maximilianocontieri.com/refactoring-002-extract-method]

# Credits

Image by <a href="https://pixabay.com/users/tumisu-148124/">Tumisu</a> from <a href="https://pixabay.com/">Pixabay</a>

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This article is part of the Refactoring Series.