1. COMPUTER 2430 Object Oriented Programming and Data Structures I

2. Container Classes
Bag
Set
Sorted List
. . .

3. Class Bag Container Can grow, but never shrink
The order of array elements is not maintained
May or may not allow duplicate elements

4. public class Bag {
private final int INIT_SIZE = ;
private final int GROWBY = 500;
private Object[] bag = new Object[INIT_SIZE];
private int numObjects = 0;
public void addObject( Object obj )
public boolean removeObject( Object obj )
private int find ( Object obj )
@Override
public String toString ()
private void grow () }

5. public class CS2430Sx {
public static void main(String[] args)
Bag myBag = new Bag();
Object obj = new Object();
// Valid?
myBag.addObject(obj);
myBag.addObject(new Date());
myBag.addObject(new Student(“Frank”)); }

6. public class Bag {
private Object[] bag = new Object[INIT_SIZE];
private int numObjects = 0;
public void addObject( Object obj )
if (numObjects == bag.length)
grow();
bag[numObjects ++] = obj; }
private void grow ()
int size = bag.length + GROWBY;
Object[] temp = new Object[size];
for (int i = 0; i < numObjects; i ++)
temp[i] = bag[i];
bag = temp;

7. public class Bag {
. . .
// Allow duplicate?
// Yes
public void addObject( Object obj )
if (numObjects == bag.length)
grow();
bag[numObjects ++] = obj; }

8. public class Bag {
. . .
// What if duplicates are not allowed?
public boolean addObject( Object obj )
if (find(obj) != -1)
return false;
if (numObjects == bag.length)
grow();
bag[numObjects ++] = obj;
return true; }
private void grow ()
private int find( Object obj )

9. It works for all classes: Polymorphism!
public class Bag {
private Object[] bag = new Object[INIT_SIZE];
/**
Finds and returns the index of element in array bag
that equals obj.
@param obj the object to be found
@return the index of the element if found, -1 otherwise */
private int find( Object obj )
for (int i = 0; i < numObjects; i ++)
if (bag[i].equals(obj))
return i;
return -1; }
It works for all classes: Polymorphism!

10. public class Bag {
private final int INIT_SIZE = ;
private final int GROWBY = 500;
private Object[] bag = new Object[INIT_SIZE];
private int numObjects = 0;
// Maintain order
public boolean removeObject( Object obj )
int index = find (obj);
if (index > -1)
-- numObjects;
for (int i = index; i < numObjects; i ++)
bag[i] = bag[i + 1];
return true; }
return false;

11. // Maintain order
public boolean removeObject( Object obj ) {
int index = find (obj);
if (index > -1)
delete(index);
return true; }
return false;
// Quiz 2
// Index is in the range and the operation will be successful!
public void delete ( int index )
-- numObjects;
for (int i = index; i < numObjects; i ++)
bag[i] = bag[i + 1];

12. public class Bag {
private final int INIT_SIZE = ;
private final int GROWBY = 500;
private Object[] bag = new Object[INIT_SIZE];
private int numObjects = 0;
// Do not maintain order
public boolean removeObject( Object obj )
int index = find (obj);
if (index > -1)
bag[index] = bag[-- numObjects];
return true; }
return false;

13. // Remove one object from the array
public boolean removeObject( Object obj ) {
int index = find (obj);
if (index > -1)
delete(index);
return true; }
return false;

14. // Remove all objects from the array that equal obj
public int removeObject( Object obj ) {
int count = 0;
int index = find (obj);
while (index > -1)
delete(index);
count ++;
index = find(obj); }
return count;

15. Any Other Meaningful Bag Methods?
public class Bag {
private final int INIT_SIZE = 10000;
private final int GROWBY = 100;
private Object[] bag = new Object[INIT_SIZE];
private int numObjects = 0;
public void addObject( Object obj )
private void grow ()
public boolean removeObject( Object obj )
public int find ( Object obj )
@Override
public String toString () }
Any Other Meaningful Bag Methods?

16. public class Bag {
private final int INIT_SIZE = 10000;
private final int GROWBY = 100;
private Object[] bag = new Object[INIT_SIZE];
private int numObjects = 0;
. . .
public boolean isEmpty()
return numObjects == 0; }
public int getCount ()
return numObjects;

17. public class Bag {
private Object[] bag = new Object[INIT_SIZE];
public Object getItem ( Object obj )
int index = find(obj);
if ( index != -1 )
return bag[index];
return null; }
Why we need this method?

18. GolfLeague theLeague = new GolfLeague();
GolfLeagueMember member = new SeniorMember(“Qi”, 80);
System.out.println(member.toString());
// The scores and handicap for Qi has changed
. . .
member = theLeague.getItem(member);

19. SortedList Class
The data declaration can be the same as that for the Bag.
private Object[] list = new Object[INIT_SIZE];
private int num = 0;
private final int GROWBY = 3;
All the Bag methods we wrote would also work as SortedList methods, but the list must be in sorted order.

20. Method add Assume in ascending order. Where to insert a new object?
index …
i i num length-1
Assume in ascending order.
Where to insert a new object?
list[0] < obj
list[1] < obj
. . .
list[i] < obj
list[i+1] > obj
Need a comparison method!

21. Method add Find the position to be added Move items down one position
index
num length-1 …
New item …
Find the position to be added
Move items down one position
Add the new item
Update num

22. Method delete Find the item (index) to be deleted
num length-1 … …
Find the item (index) to be deleted
Move items up one position
Update num

23. Sort Method

24. Search Method

25. Quiz 2

26. Lab 3
Submission

27. Prog 2