Java Code Conventions: must match pattern '^[a-z][a-zA-Z0-9]*$'

^[a-z][a-zA-Z0-9]*$

This regex describes something which starts with lowercase and the remainder is composed of uppercase, lowercase, and numbers. (Examples: aVariable, variable, aNewVariable, variable7, aNewVariable7.)

If you want your field to be constant and static, use:

static final String ADD = "Add text";

Otherwise, use:

final String add = "Add text";

If it is a constant you want, it should also be static

static final String ADD = "Add text";

Constants normally use uppercase letters, but since your variable was not static, it was not interpreted as a constant.