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I'm looking to switch 2 random characters in a string. For example, if I start with "abcdef", I'd like the computer to generate 2 random numbers, and switch 2 characters. So a possible outcome could be "afcdeb".

Harrison Bergman
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3 Answers3

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  1. get the length of the string
  2. get 2 different int random numbers between 0 and the length of the string: rand1 and rand2.
  3. I think you should convert the string to an array of chars.
  4. Do the swap within the array with the 2 random numbers.
  5. Convert the array to a string.
user6201852
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You can use the following approach using the StringBuilder.

String string="Your String";
int length=string.length();

Random rand=new Random();
int one=0;
int two=0;
/*
generate two random indexes which are not equal to each other.
*/
while(length>=2 && one==two){
    one=rand.nextInt(length);
    two=rand.nextInt(length);
}

//use String builder and interchange the characeters.
StringBuilder builder=new StringBuilder(string);
builder.setCharAt(one,string.charAt(two));
builder.setCharAt(two,string.charAt(one));

String newString=builder.toString();
Imesha Sudasingha
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  • Sorry to be a pain, but is there a way to do it without StringBuilder? – Harrison Bergman Apr 15 '16 at 04:32
  • There's a way. You an concatenate substrings and create the new string. But the code will be bit complex. As in [this](http://stackoverflow.com/questions/6952363/replace-a-character-at-a-specific-index-in-a-string) question – Imesha Sudasingha Apr 15 '16 at 04:36
0

Generate random numbers index1 and index2 between 0 and (length of string -1)

int index1= randomNumber1;
int index2= randomNumber2;

String str ="abcdef";
String charSwap1= str.substring(index1, index1+1);
String charSwap2= str.substring(index2, index2+1);
StringBuilder builder=new StringBuilder();
builder.append(str);
builder.replace(index1,index1+1,charSwap2);
builder.replace(index2,index2+1,charSwap1);
System.out.println(builder.toString());
annu
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  • This returns an error in String charSwap1= str.substring(index1, index1+1); String charSwap2= str.substring(index2, index2+1); The index is out of range – Harrison Bergman Apr 17 '16 at 20:50
  • startIndex is inclusive whereas the endIndex is exclusive.. It should not return any error as index+1 will be 2 in your case and index2+1 should be 6 which is within the string range. Are you getting error for charSwap2 or charSwap1 ?? If for charSwap2 use this instead. str.substring(index2) if it is the last character. – annu Apr 18 '16 at 04:48