Hi,
As having past java experience, we usually create separate file for CONSTANTS & their VALUES. Since we have "CUSTOM LABELS" in Salesforce to get String KEY & VALUE but we don't want these CONSTANTS to be change in future from SETUP. Also, Hard-Coding values are always bad practice and we have kept all this CONSTANTS in separate global class named "Global_Constants" where each constants is marked with static, final & assigned with value. 
Also, I had created getter method to access this static constant variable but whenever we try to access this, we receive error message as "variable_name does not exist". 
Can you please let us know, How can we create global page class like $User, $Label in Apex ?? OR
How can we access these CONSTANTS on VFPage without using these class as "Controller / Extensions" (Since I want to make it separate, global & to be accessible in every page)

Thanks.