Retrieving the first item in list

[Douglas Wolfinger]

I am using a class ListArrayBased to define the add() and get() methods. I would like to know how to retrieve the first item. The items are added from the list position of 1, and get() throws an exception if I specify get(0).
The purpose of the class is to sum the items in the list.

  class ListSum extends ListArrayBased {
  ListArrayBased lab = new ListArrayBased();
  public Object listMeth() {
    lab.add(1, new Integer(3));
    lab.add(1, new Integer(6));
    lab.add(1, new Integer(9));
    lab.add(1, new Integer(12));
    return lab; 
   }
  public void sumMeth() {
   int x=0;
   int y=0;
   for(int i=1;i<lab.size();i++) {
     //if i<1 get throws a ListIndexOutOfBoundsException
     Integer integer = (Integer)lab.get(i);
     y = integer.intValue();
     x += y;
     System.out.println("x = " + x);
   }
  }
  public static void main(String args[]) {
    ListSum ls = new ListSum();
    ls.listMeth();
    ls.sumMeth();
   }
  }

[ September 18, 2002: Message edited by: Douglas Wolfinger ]

[Barry Gaunt]

Sorry can't guess the implementation of ListArrayBased.
What happens when you replace lab.add(1,...) by lab.add(0,...) where it appears.
-Barry
[ September 18, 2002: Message edited by: Barry Gaunt ]

[Doug Wolfinger]

Here are the get and add methods. numItems is equal to the size of the list. This is how the code is written in the text. The index has to be one less than the position. Thanks.

  public void add(int index, Object item) 
                  throws  ListIndexOutOfBoundsException {
    //MAX_LIST is a hard coded maximum number of items
    if (numItems > MAX_LIST) {
      throw new ListException("ListException on add");
    }  // end if
    if (index >= 1 && index <= numItems+1) {
      // make room for new element by shifting all items at 
      // positions >= index toward the end of the 
      // list (no shift if index == numItems+1)
      for (int pos = numItems; pos >= index; pos--) {
//          pos++;
          items[translate(pos+1)] = items[translate(pos)];
          System.out.println(translate(pos));
      } // end for
      // insert new item
      items[translate(index)] = item;
      numItems++;
      System.out.println("item from add meth = " + item);
    } 
    else {  // index out of range
      throw new ListIndexOutOfBoundsException(
       "ListIndexOutOfBoundsException on add");
    }  // end if
  } //end add
   
  public Object get(int index) 
                    throws ListIndexOutOfBoundsException {
    if (index >= 1 && index <= numItems) {
      return items[translate(index)];
    }
    else  {  // index out of range
      throw new ListIndexOutOfBoundsException(
       ListIndexOutOfBoundsException on the get. Index must be > 0");
    }  // end if
  } // end get

[Doug Wolfinger]

I've solved it. I should have had the for loop counting down

int length=lab.size();
for(int i=length;i>0;i--)

Thanks!