---
id: Lombok
aliases: []
tags:
  - java
  - lombok
  - dev
date: 2025-10-19T22:27:35
title: Lombok
---
# Lombok
[Project Lombok](https://projectlombok.org) is a java library that extends editors and IDEs with useful 
features and can also improve the language itself.

## Extension Methods
Consider the following class:
```java
  public final class DoubleExtensions {
    /**
     * round the double n to d decimals
     * @param n input number
     * @param d number of decimal places to consider
     * @return 
     */
    public static double roundAt(double n, int d) {
      final var s = Math.pow(10, d);
      return Math.round(n * s) / s;
    }
 
    /**
     * truncate the double n at d decimals<br>
     * like roundAt() but does not mathematically round
     * @param n
     * @param d
     * @return 
     */
    public static double truncateAt(double n, int d) {
      final var s = Math.pow (10, d);
      return Math.floor(n * s) / s;    
    }
  }
```
It can be used to extend the Java class `Double` with methods `roundAt(x)` and `truncateAt(x)` to round 
or truncate decimal places to `x`.

To use this, you must annotate your consumer class with `@ExtensionMethod(DoubleExtensions.class)` and 
import `lombok.experimental.ExtensionMethod`. The feature is considered experimental and may contain 
issues, but normally works well enough to be used in production code.