在第一次成功添加后在 for 循环中添加到 ArrayList 时应用程序崩溃

Question

Still new to android and java but getting there, here is my problem.

The crash occurs at this point fieldsA.add( A.substring(_start, _a[i])); it works the first time but not the second time, I do not get an error in my debug window, just a crash.

// number of chars to extract from string value to add to ArrayList.

int _a[] = {12,8,8,8,24,24,8,8,4,4,4,5,5,5,7,7,7,7,4,4,4,7,7,7,7,4,8,8,8,1,1,1,1,2};

int _b[] = {2,32,32,4,4,4,5,5,5,7,7,7,7,4,4,4,8,1,4,4,4,4,1,4,56,14 };

for clarity, _start value is correct and length of string to extract (_a[i]) is also correct, in the case of this crash, _start value is 12 and _a[i] is 8 so the substring(12, 8) should add "12663312" to the ArrayList.

Question is, what am I doing wrong in how I am using array list, if I was using a vector (which I would normally do in C++) it would be a breeze but this is my first time use of ArratList in java and I cant see what the problem is, maybe I am too old.

Thanks in advance.

public void SetEkmFieldValueStrings(String A, String B)
  {
  // example string A content
  /* $00030000019412663312012914320863457705827487016831160515448803478652000007590515438109551618066451002454245424540005600000000300000984000000000007720001756 100C000 100000003800000000000056000009450020000001600000000000000000232002210030208144700!*/

  /* if length of A is less than 250 chars, read is no good, discard
  *  NOTE:  both Strings A and B will need to be validated for checksum
  *  TODO...
  * */
  if(A.length() < 250) {return;}

   // discard first 4 chars from string, not needed
   A = A.substring(4, A.length()-4);

   /* array of fields values are NOT empty */
   /* clear arrays for new sets of values */
  if(fieldsA.size() > 0)
    fieldsA.clear();
  if(fieldsB.size() > 0)
    fieldsB.clear();;

  int _start = 0; /* 1st index into field size array */
  int i;
  for(i = 0; i < _a.length; i++)
    {
    /*  add the substring of String A to the array list of field values
    *   _a[i] contains the length of string to extract from A
    * */
    fieldsA.add((String) A.substring(_start, _a[i]));
    String j = fieldsA.get(_start);  //for testing purpose only
    /* set _start to the next field start pont in string A */
    _start += _a[i];
    }

    /* do same for String B*/
    _start = 0;
    for(i = 0; i < _b.length; i++)
      {
      /*  add the substring of String A to the array list of field values
       *   _b[i] contains the length in of string to extract
       * */
      fieldsB.add(B.substring(_start, _b[i]));
      /* set _start to the next field start pont in string A */
      _start += _b[i];
      }

  }

Answer 1

Looks to me that You use wrong indexes for substring.

Substring method second parameter is not count of chars to take but endIndex .

We can find relevant info in javadoc of String.substring:

public String substring(int beginIndex, int endIndex)

beginIndex - the beginning index, inclusive.

endIndex - the ending index, exclusive.