> For the complete documentation index, see [llms.txt](https://peterlulu666.gitbook.io/the-complete-salesforce-development-course/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://peterlulu666.gitbook.io/the-complete-salesforce-development-course/final.md).

# Final

```apex
// Declare Constant Variable
final Decimal PI;
System.debug(PI); //prints null

// initialize variable
PI = 3.14159;
System.debug(PI);

// update variable value - NOT ALLOWED
PI = 2.14159;
System.debug(PI);
```