how to access a java variable in strings.xml

How can I access a static java variable in a resource in strings.xml in the android studio?

I have a variable like this:

public static final String NUM_OF_DAYS = "10";

Now, I want to use this somehow in strings.xml in a resource.

EDIT:

I just want to use the string.xml resource (which will access NUM_OF_DAYS) in a java file.