Comp 271 lab 2 - Lists of Strings
- Introduction to Arrays
- Introduction to for loops
This lab deals with a class StrList, which is supposed to work a lot
like ArrayList<String>. But
some things need fixing. You will implement StrList in both
Java and C++.
The strings themselves are stored in an array elements[
]. Not all of the array is necessarily used; only the first currsize
slots are (elements through elements[currsize-1]). The variable currsize
thus represents the active length of the StrList not elements.length.
This way our StrList can easily grow in length, at least up until the hard
limit of elements.length. The main task of this lab is to grow past
I've given you a starter/demo project in BlueJ, lists.zip,
and C++ (StrList.cpp) to get started. The latter
is also available as an Xcode project, cpplists.zip.
These both contain the following methods:
The project also contains class WordTest to add a bunch of words to a list,
thus testing your add() method. StrList.cpp has a function main() to do the
- add(string y)
- String get(String n)
- void set(int n, String val)
- int size()
- void print()
You are to do the following:
1. Make add() work even when elements is full
The trick here is to allocate a new array, say newelements,
of larger size (doubling works, or increasing by 10, or increasing by 1.5
although that's trickier because of the floating-point conversions):
 newelements = new string[newsize];
Next you copy from elements[i]
for i<currsize. This is done
with a straightforward for or while loop. Finally, you
replace elements by newelements:
elements = newelements
does it. Note that in Java there is no need to do anything with the "old" elements. In C++ you should call delete on it; see the destructor
~StrList for an example.
At this point, you now have space to add the new item, so you go ahead
and do it. The overall add structure looks like:
if (currsize ==
// do the space expansion as above
to ensure room
// now add the usual way; one way or another we know there
elements[currsize] = y;
currsize += 1;
Once you do this, the program should behave quite differently; you
shouldn't get those "no more room to add ...." messages, and the entire
list should print out.
In C++ there is no analogue of elements.length.
You will have to keep the current allocated size of the array elements
in a third instance variable, capacity.
For the C++ version, don't forget to delete
the old array!
2. Add a fill() method
Create a method void fill(string val) that is like Add(val)
until the current capacity is reached. That is, element[i]
is set to val provided i>currsize and i<elements.Length
(or i<capacity in the C++
version). I suppose calling it Fill()
rather than fill() would be
With this, the following combination would create a list of 10 empty
StrList sl = new
StrList(10); // currsize = 0 but potential capacity =
Submit your work on Sakai (or via email) by putting it all into a zip file.