Question

So i am creating a class for “MiniString” which is just full of instance methods for the object MiniString, every MiniString has an instance variable that is a char[]. When testing my methods, I can’t find where I am going wrong with my substring() method. There are two substring methods where one takes a parameter of int and the other takes two int parameters. I keep getting the error on the one int parameter method. The substring method is supposed to return a new MiniString formed of the characters between the position in the target Ministring specified by the int parameter, and the end of the target MiniString. The error I keep getting in my JUnit Tester is the following:

java.lang.ArrayOutofBoundsException:22
at MiniString.substring(MiniString.java:141)
at MiniString.substring(MiniString.java:159)

Here are my constructors for the object MiniString:

private char[] miniscule;

 MiniString(char[] array){
  int i = 0;
  miniscule = new char[array.length];
  while (i < array.length){
   miniscule[i] = array[i];
   i++;
  }
 }
 MiniString(String string){
  int i = 0;
  miniscule = new char[string.length()];
  while (i < string.length()){
   this.miniscule[i] = string.charAt(i);
   i++;
  }
 }

and here is the code for the two substring() methods:

public MiniString substring(int start, int end){
  int i = start; 
  if (end > start){
   char[] temp = new char[end - start];
   MiniString range = new MiniString(temp);
   while (i < end){
    range.miniscule[i] = this.miniscule[i];
    i++;
   }
   return range;
  }
  else{
   char[] temp = new char[1];
   MiniString range = new MiniString(temp);
   range.miniscule[0] = 0;
   return range;
  }
 }
 public MiniString substring(int position){
  int start = position;
  int end = this.miniscule.length;
  char[] temp = new char[end - start];
  MiniString output = new MiniString(temp);

  output = substring(start, end);
  return output;
 }

Thanks for your help!

Answer 1

In your first substring method, the line

range.miniscule[i] = this.miniscule[i];

is the most likely suspect. I expect you really want

range.miniscule[i - start] = this.miniscule[i];

String has substring methods that do approximately what you’re doing here, but I presume you’re doing this to learn, rather than reinventing string handling for a production use.

If you’re using Java 6, you might also want to look at the Arrays.copyOfRange(T[] ts, int i, int i1) method, which does most of the work you’re doing in your substring methods.