Stupid question about comparing lists

[KingJaymz]

Hello all. I was hoping that you could help me. I have to write a merge method that merges a new sorted list to the current list. The new list is the only parameter of the method. So this is my question. I should probably know the answer, but how can I compare the parameter to the existing list? They're both entitled list, so I'm slightly confused. This is the code, if it will help, but I'm nowhere near finished with the merge method.

package ch03.genericLists;

public class SortedList extends List
{
public SortedList(int maxItems)
// Instantiates and returns a reference to an empty list object with room for maxItems elements.
{
super(maxItems);
}

public SortedList()
// Instantiates and returns a reference to an empty list object with room for 100 elements.
{
super(100);
}

public boolean isThere (Listable item)
// Returns true if an element with the same key as item is on this list, otherwise returns false.

{
int compareResult;
int midPoint;
int first = 0;
int last = numItems - 1;
boolean moreToSearch = (first <= last);
boolean found = false;

while (moreToSearch && !found)
{
midPoint = (first + last) / 2;
compareResult = item.compareTo(list[midPoint]);

if (compareResult == 0)
found = true;
else if (compareResult < 0) // item is less than element at location
{
last = midPoint - 1;
moreToSearch = (first <= last);
}
else // item is greater than element at location
{
first = midPoint + 1;
moreToSearch = (first <= last);
}
}

return found;
}

public Listable retrieve(Listable item)
// Returns a copy of the list element with the same key as item
{
int compareResult;
int first = 0;
int last = numItems - 1;
int midPoint = (first + last) / 2;
boolean found = false;

while (!found)
{
midPoint = (first + last) / 2;
compareResult = item.compareTo(list[midPoint]);

if (compareResult == 0)
found = true;
else if (compareResult < 0) // item is less than element at location
last = midPoint - 1;
else // item is greater than element at location
first = midPoint + 1;
}

return list[midPoint].copy();
}

public void insert (Listable item)
// Adds a copy of an item to this list.
{
int location = numItems - 1;
boolean moreToSearch = (location > -1);

while (moreToSearch)
{
if (item.compareTo(list[location]) > 0) // item is greater
moreToSearch = false;
else // item is less
{
list[location + 1] = list[location];
location--;
moreToSearch = (location > -1);
}
}
list[location + 1] = item;
numItems++;
}

public void delete (Listable item)
// Deletes the element that matches item from this list.
{
int location = 0;

while (item.compareTo(list[location]) != 0)
location++;

for (int index = location + 1; index < numItems; index++)
list[index - 1] = list[index];

numItems--;
}

public void merge(SortedList list)
{
int newSize = numItems + ;
int location;
boolean moreToSearch;
}
}


Please let me know if you need any more information. Thank you. Your help is very much appreciated.

[dlorde]

I'm not exactly sure what you're asking, but the argument to the method is a SortedList called 'list' and the SortedList instance with which it is being merged (i.e. the instance whose merge method is being run) can, if necessary, be referred to in the method as 'this', although class members can be referenced directly, so this shouldn't be necessary.

Incidentally, why such strange method names? Usually add(object) adds an object, contains(object) checks if the item is present, get(index) retrieves it, and remove(object) removes it from the list...

Your retrieve(...) and isThere(...) methods could share their code - surely retrieve(...) checks if the object is there, and then returns a copy. Since two objects with the same key should have the same value, all it needs to do is:Listable retrieve(Listable item) {
if (!isThere(item)) {
return null;
}

return item.copy();
}I couldn't see what your retrieve(...) method does if the item isn't found... and why copy() rather than implementing the clone() method from Cloneable?

The first step towards wisdom is calling things by their right names...
Chinese proverb.

[KingJaymz]

Ok, so I have another question now. My SortedList class won't compile when it's in the directory that it seems to need to be in. This is the initial (and I'm guessing proper) directory tree:

ch03\genericLists\ List.java
Listables.java
ListCircle.java
ListString.java
SortedList.java

When SortedList is in the same folder as the rest (where it started), it won't compile properly. However, if SortedList.java is inserted into the ch03 folder, it compiles nicely. Is there a reason that I can't figure out that this is happening? Thank you.

Edit: Sorry, I can't get the files to line up properly. :blush: