Java - Reversing a string with recursion [duplicate]

Question

private static String stringReverseRecursive(String str)
   {
       // saves the last letter of the word in the variable c
    char c = str.charAt (str.length()-1); 
       // take the last letter saved in c and joins the sub string of everything without the first letter and runs it again.
       return c + stringReverseRecursive((str.substring(0,str.length()-1))); 

   }

When I try to call the function then the compiler gives me an error saying that it goes out of range. I think there is something wrong with the lat line and the char c line.

Hi, Recursive methods need a base case where if it's true the recursion ends... Otherwise it won't stop executing until an error such as the one you've described above happens or max stack depth is reached e.g. if (str.length() == 0) { return str; } If you're looking for more info on recursion, you can give this a read: tripwiretech.blogspot.co.nz/2014/09/… — TripWire
– TripWire, Commented Oct 25, 2017 at 1:49
What happens if you reverse the empty string? Because your recursive call will always reduce to a call with the empty string, and if you don't handle that special case, your method doesn't work at all. — Erwin Bolwidt
– Erwin Bolwidt, Commented Oct 25, 2017 at 1:49
@TripWire do you mean that I should put everything in the method in else — Diya Saha
– Diya Saha, Commented Oct 25, 2017 at 1:52
Are you trying to reverse a string, as the method name implies, or are you trying to find the last letter of a string? — Tim Biegeleisen
– Tim Biegeleisen, Commented Oct 25, 2017 at 1:59
"the compiler gives me an error" no, it doesn't. What you're seeing is a runtime error. — Andy Turner
– Andy Turner, Commented Oct 25, 2017 at 2:13

TripWire · Accepted Answer · 2017-10-25 02:42:23Z

1

private static String stringReverseRecursive(String str)
{ 
    if (str.isEmpty()) {

        return str;
    }

   // saves the last letter of the word in the variable c
   char c = str.charAt (str.length()-1); 
   // take the last letter saved in c and joins the sub string of everything without the first letter and runs it again.
   return c + stringReverseRecursive((str.substring(0,str.length()-1))); 

}

You want to check if the length is 0, to cater for an empty string e.g. ""

The if statement allows your code to complete execution and can be referred to as the base case.

edited Oct 25, 2017 at 2:42

answered Oct 25, 2017 at 1:58

TripWire

5821 gold badge7 silver badges18 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Elliott Frisch Over a year ago

I'd prefer String#isEmpty() to a length() == 0 test.

TripWire Over a year ago

Thanks Elliott, that is better and I’ve updated my answer!

Collectives™ on Stack Overflow

Java - Reversing a string with recursion [duplicate]

1 Answer 1

2 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Linked

Related