CSE116 / CSE504
Introduction to Computer Science II
Dr. Carl Alphonce
343 Davis Hall
alphonce@buffalo.edu
Office hours:
Thursday 12:00 PM – 2:00 PM
Friday 8:30 AM – 10:30 AM
OR request appointment via e-mail
PROFESSIONALISM
Turn off and put away electronics:
cell phones
pagers
laptops
tablets
etc.
© Dr. Carl Alphonce
ANNOUNCEMENTS
Sign up for Piazza (up to 95% registration)
15 students have still not signed up
piazza.com/buffalo/spring2016/cse116
Recitation
Write-ups are starting this week
Write-Up Grading
If your submission scores 100% on automated grading, you
receive 100%.
If your submission does not score 100% on automated
grading, then
(i) the automated grade does not count, and
(ii) your submission goes for manual grading.
In manual grading the outcome will be one of four grades:
100 – a correct solution
70 – submission is on the right track, but is has errors
30 – submission is wrong, but related to problem
0 – no submission, or unrelated to problem
ROADMAP
Last class
defining the MultiSet
managing memory in array
invariant properties
Today
defining the MultiSet
Coming up
defining the MultiSet
public class MultiSet<E> implements Collection<E> {
MultiSet<E> development
STEP 2: array for storage
private E[] _store;
private int _size;
public MultiSet() {
_store = (E[]) (new Object[10]);
_size = 0;
}
@Override public boolean add(E e) {
_store[_size] = e;
_size = _size + 1;
return true;
}
@Override public int size() {
return _size;
}
// rest of class body omitted
}
MultiSet<E> development
runtime view
MultiSet<Jlabel> b = new MultiSet<Jlabel>();
b
_store
INVARIANT PROPERTIES
_size indicates:
_size
• the number of
elements in the
MultiSet
3
0
1
• the first available
position in _store
2
occupied
region
3
4
5
6
7
available
region
8
9
Invariants
An invariant property of a class must hold between
method invocations:
• A constructor must establish the invariants.
• If a method breaks an invariant it must restore it
before exiting.
Invariants of our class:
• _size indicates the number of elements in the
MultiSet
• _size refers to the first available position in the
_store
© Dr. Carl Alphonce
re-size
On to eclipse to deal with re-size issue.
© Dr. Carl Alphonce
public class MultiSet<E> implements Collection<E> {
Observation
private E[] _store;
private int _size;
Classroom coding
Invariants break here when
_size == _store.length
(because _size does NOT
public MultiSet() {
refer to an available
_store = (E[]) (new Object[10]);
position in the array _store
_size = 0;
points to).
}
@Override public boolean add(E e) {
_store[_size] = e;
_size = _size + 1;
return true;
}
@Override public int size() {
return _size;
}
// rest of class body omitted
}
© Dr. Carl Alphonce
public class MultiSet<E> implements Collection<E> {
private E[] _store;
private int _size;
Resolution
Classroom coding
if (_size == _store.length) {
// allocate larger array
public MultiSet() {
// copy data
_store = (E[]) (new Object[10]);
}
_size = 0;
}
@Override public boolean add(E e) {
_store[_size] = e;
_size = _size + 1;
return true;
}
@Override public int size() {
return _size;
}
// rest of class body omitted
}
© Dr. Carl Alphonce
Classroom coding
@Override public boolean add(E e) {
_store[_size] = e;
_size = _size + 1;
if (_size == _store.length) {
E[] temp = (E[]) (new Object[_store.length * 2]);
for (int i=0; i<_store.length; i=i+1) {
temp[i] = _store[i];
}
_store = temp;
}
return true;
}
© Dr. Carl Alphonce
Exercise for next class
Define the contains method.
© Dr. Carl Alphonce