Java: How to fix "String index out of range: #"?

Question

I'm attempting to scramble two random letters of a string which isn't the first letter, or last two. I'm getting a "String index out of range" error when compiling. I've tried workshopping many different solutions, but nothing seems to work.

For this assignment, we have to use a method and .charAt commands. I've tried creating variables for the two random characters then adding them back into the string flipped, but couldn't get that to work either.

public static String scramble(String input) {
    int range = input.length() - 3;
    int place = (int)(Math.random() * range);
    String newWord = "";
    newWord = input.substring(0, place);
    newWord = newWord + newWord.charAt(place) + 2;
    newWord = newWord + newWord.charAt(place) + 1;

    return newWord;

I'm expecting an output of a string with two of its characters scrambled. For example, "Fantastic" would be "Fantsatic", or "Fnatastic".

Make sure the "place" value is not greater than string length before you call .chartAt — kosa, Mar 26 '19 at 16:36

score 0 · Answer 1 · answered Mar 26 '19 at 16:49

0

You do :

newWord = input.substring(0, place);

So the indexes inside newWord goes from 0 to place-1
Then you do:

newWord.charAt(place);

But this index does not exist in your String. It is Out of Bound

See the doc

answered Mar 26 '19 at 16:49

vincrichaud

2,218
17
34

score 0 · Answer 2 · answered Mar 26 '19 at 16:51

When you create newWord = input.substring(0, place) it has exactly place characters. You can't request charAt(place) from it, the last character is at place-1.

If you want to swap characters convert input to char[] and generate random indexes to swap.

String input = "Fantastic";

// random constraints
int min = 1;
int max = input.length() - 3;

// random two characters to swap
int from = min + (int) (Math.random() * max);
int to;
do {
    to = min + (int) (Math.random() * max);
} while (to == from); // to and from are different

// swap to and from in chars
char[] chars = input.toCharArray();
char tmp = chars[from];
chars[from] = chars[to];
chars[to] = tmp;
String result = new String(chars);

System.out.println(result); // Ftntasaic

Rupesh Agrawal · Answer 3 · 2019-03-27T08:05:08.343

0

you can try

  public static String scramble(String input) {
    if(input.length() >3){
        int range = input.length() - 3;
        int place  = 1+   new Random().nextInt(range) ;
        input=input.substring(0, place) +input.charAt(place  + 1)+input.charAt(place) +input.substring( place+2);

    }
    return input;
}

input: Fantastic output : Fanatstic , Fatnastic ,Fanatstic

edited Mar 27 '19 at 08:05

answered Mar 26 '19 at 17:13

Rupesh Agrawal

645
8
22

score 0 · Accepted Answer · answered Mar 27 '19 at 08:12

Try something like this:

public static String scramble(String input) {
    int range = input.length() - 3;
    int place = (int)(Math.random() * range);
    String newWord = input.substring(0, place);
    newWord = newWord + input.charAt(place + 1);
    newWord = newWord + input.charAt(place);
    // if you need the whole input, just 2 characters exchanged, uncomment this next line
    // newWord = newWord + input.substring(place + 2, range);
    return newWord;
}

Java: How to fix "String index out of range: #"?

4 Answers4