I am supposed to write recursive program. I have done this below, however I don't know if my understanding of recursion is correct. I believe that it is a method which calls this method inside. In my case (insertCommas).

private String insertCommas(String str)
        if(str.length() < 4){
            return str;
        return insertCommas(str.substring(0, str.length() - 3)) + "," + str.substring(str.length() - 3, str.length());

Is my program recursive?


The most common type of recursion is what we call "tail recursion" - a function directly calling itself, which is what you are doing here. There is indirect recursion where a function A calls function B, which somewhere down the line agains calls to function A.

So, yes your FUNCTION is recursive. A recursive program is something else entirely... :-)

As rubberman said, yes it is recursive. If you ask whether it is correct, I would say no. Have you tested it? If a string "1234" goes in, what would be your result? If a string "1234567890123" goes in, what would be your result?

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