CODEWITHSUNDEEP
javarecursionmethodscommand-linereturn
Asia x3
Asia x3

Reputation: 616

Recursive method return numbers from int to 0

I'm having trouble with a recursive method that will return and print in my main method the numbers from X (X being a int on commandline) to 0. Returning the numbers as a String.

For example my commandline argument is 4. My output should be: 4, 3, 2, 1, 0

I kind of understand how to reverse a string like: "123" to "321".. But no clue when getting a integer like 3, and returning it like "3, 2, 1, 0" as a string. :o

My code atm:

public static void main(String[] commandlineArguments) {
      if (commandlineArguments.length == 0) {
         System.out.println("Please enter a least one commandline!");
      } 
      else {
         Integer number = new Integer(0); // initialize number
         try {
            number = Integer.parseInt(commandlineArguments[0]);
         } 
         catch (NumberFormatException exception) { // NumberFormatException
            System.out.println(exception + " is not a integer!");
            System.exit(1); // end program
         }
         String reverse = reverse1(number);
         System.out.println(reverse);
      }
   }

   public static String reverse1(Integer number){
      if (number == 0){
         return "";
      } 
      else{
         return "";
      }
   }

}

Upvotes: 0

Views: 156

Answers (2)

Mikescher
Mikescher

Reputation: 893

public static String reverse1(int number){
   if (number == 1){
      return "1";
   } else {
      return number + ", " + reverse1(number - 1);
   }
}

The trick with recursion is - in my opinion - always to search the trivial case. So here the easiest input is 1 and the result would be "1"

reverse1(1) = "1";

And then you need that "strange" recursion step where you reduce your input towards that trivial case.

reverse1(n) = n, reverse(n-1)

Here you just say:

The result of a number n is always the result of "this number minus 1" with that extra number n in front.

Think about it, its quite logical.

It's sometimes not easy to think of a problem in that "recursive way". But often it makes things alot easier.

Upvotes: 5

RaceBase
RaceBase

Reputation: 18848

public static void main(String[] commandlineArguments) {
    printNumber(number);

}

public static String printNumber(Integer number){
    if (number == 0){
       return "0";
    } 
    return number +" " + printNumber(number-1);
}

Upvotes: 2

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