Java design pattern to keep a formula in a property file

I have property file(key/value) pair from where I currently read a value against a key and display that value as it is in the UI .

The complexity have increased,Now the value is more dynamic based on some formula. The formula includes a variable parameter whose value I will get at run time.

Is there any java design pattern to design this scenario .

I was thinking to put a method name in the property file against a key.

Now I will read the key and fetch the method name . This method will calculate the value for that particular key.

Please let me know your suggestion