---
title: Validated Expressions
---
Fzzy Config has a math engine called `Expression`. See the [Expressions](../../features/Expressions) article for more details. Validating expressions works like other validation, `ValdiatedExpression` wraps a default expression and allowable characters into a `ValidatedField`.
```java !!tabs Java
// example validated Expression; automatically parses and caches the Math Expression input in string form.
// The user can input any equation they like as long as it uses x, y, both, or neither expected variables passed in the set
ValidatedExpression validatedExpression = new ValidatedExpression("2.5 * x ^ 2 - 45 * y", Set.of('x', 'y'));
```
```kotlin !!tabs Kotlin
// example validated Expression; automatically parses and caches the Math Expression input in string form.
// The user can input any equation they like as long as it uses x, y, both, or neither expected variables passed in the set
var validatedExpression = ValidatedExpression("2.5 * x ^ 2 - 45 * y", setOf('x', 'y'))
```
See the documentation page here 🗗