php class constant visibility

Update: visibility modifiers for constants have been added in PHP 7.1 (to be released in December 2016 according to PHP's release policy). See the RFC : Support Class Constant Visibility.

An alternative would be to use a Constant Method, e.g.

private static function gravitationalConstant() {
    return 9.81;
}

Quoting from Fowler's Refactoring book:

This idiom is less familiar to C based programmers, but is very familiar to Smalltalkers (who didn't have constants in their language). On the whole I don't tend to use this in Java as it is less idiomatic to the language. However if you need to replace the simple return with a calculated value then it's worth changing the constant field to a constant method. (I guess there should be a refactoring for that....)

Modifiers are not allowed for constants in php. You can use

public static $variable = "abc";

but sadly final is not allowed here.

It is now possible in PHP 7.1 released Alpha today which adds Class constant visibility modifiers

In PHP Latest version (PHP 7.1.0) it will available.

Sample Syntax was like.

class Token {
    // Constants default to public
    const PUBLIC_CONST = 0;

        // Constants then also can have a defined visibility
        private const PRIVATE_CONST = 0;
        protected const PROTECTED_CONST = 0;
        public const PUBLIC_CONST_TWO = 0;

        //Constants can only have one visibility declaration list
        private const FOO = 1, BAR = 2;
}

Refer below link. https://wiki.php.net/rfc/class_const_visibility