What means this Regex? [duplicate]

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• Reference - What does this regex mean? 1 answer

new RegexPattern(SK_PHONE_COMBINER.combine(Collections.singletonList("02"),
    "^(%s)(\\s)?([0-9](\\s)?){7}[0-9]"), PHONE_LANDLINE, null, Country.SK);

I have this code as an artwork but i cant figure out what .combine and .singletonList parts means. Can someone explain ?

The regex should be comparing strings with legal Slovakia telephone number format.

Three parts after regex means: type of number, validation function or not, country.