public static void String replacement (String ori, String r, String w)

This method should replace all occurrences of the String r with the String w if the total length of String r (number of ocurrence X r.length()) is less than 30% of the length of ori String; otherwise, you are going to replace all ocurrences of w with r. Then return a String after applying these rules:

replacement("Skiiing is fun", "fun","cool") should return "Skiing is cool"

replacement("AAABB","A","C") should return "AAABB"

replacement("AAABB", "A","B") should return "AAAAA"