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[Derek Szpik]

I have a method:
public MySet union(MySet s){...}

And it joins two sets together, so this method is declared by:

mySet=mySet.union(unionSet);
(alternativly, it could be called with mySet=unionSet.union(mySet);)

I'm implementing the abstract interface MySet using arrays, so each set has an arrElements, which is an array of all of their elements that is created at the same time the sets are initialized.

Inside of the union method, arrElements just refers to the arrElements of mySet, and I need to know how to access the arrElements of unionSet in order to manipulate the values. Does anybody know how I would do this?

[Garrett Rowe]

You have to qualify the access using the reference identifier:

s.arrElements

[Derek Szpik]

I had tried that, and it didn't work. After hearing the suggestion form somebody else, I decided to play around with it for a bit. MySet is an interface, and doesn't have a constructor, so when I declare 'MySet unionSet' I need to use =new MyArraySet(); since MyArraySet implements MySet. So when the method union required MySet s, there was no arrElements. I had to change it to union(MyArraySet s){...} in order to access the arrElements. Thanks for the confirmation.

Well, remember how MyArraySet needs to implement MySet? By changing union(MySet s) into union(MyArraySet s), MyArraySet no longer implements MySet because the method requires a diferent input. And the real kicker here is that I can't change MySet's union to require an input of MyArraySet because after I implement MySet with arrays, I need to do it with linked lists. This does not make me happy. I'll throw down some code to show what I mean.

interface MySet{
boolean isIn(int v);
void add(int v);
MySet union(MySet s);
void printSet();
}

class MyArraySet implements MySet{
MyArraySet(){
//constructor code here.
}
boolean isIn(int v){
//binary search for int v in the set. Return true or false depending.
}
void add(int v){
//add v to the front of the set.
}
MySet union(MySet s){
//Add all elements of two sets together, make sure that no values are repeated.
}
void printSet(){
//print the set
}

This version of MyArraySet implements MySet.

interface MySet{
boolean isIn(int v);
void add(int v);
MySet union(MyArraySet s);//the only difference in these two code segments is that this uses MyArraySet as the input for union
void printSet();
}

class MyArraySet implements MySet{
MyArraySet(){
//constructor code here.
}
boolean isIn(int v){
//binary search for int v in the set. Return true or false depending.
}
void add(int v){
//add v to the front of the set.
}
MySet union(MySet s){
//Add all elements of two sets together, make sure that no values are repeated.
}
void printSet(){
//print the set
}

This version of MyArraySet does NOT implement MySet. The only difference is the input of union form MySet to MyArraySet, but it's a big enough change.

[strikethrough]So, the new problem is: how can I get this to work? My idea to be tested at the moment is to change the name of union to something like.. 'sneaky'. THEN, I can make a new method called union, and all that union does is call sneaky. how does that sound? It doesn't solve the spirit of the problem, but it does work around it nicely.[/strikethrough]
(yes, I know there is no strikethrough on this)

So, I just looked at it, and my union is set up SO WELL that I just can't force myself to do ^^. Now, I'm back to the original problem, but with more info, and a clearer question.

I have MySet union(MySet s){...}

When the input MySet is first created, it's done by:
MySet s = new MyArraySet();

What I need to do, is turn the input MySet s into a MyArraySet. How would I do this?

[Ernest Friedman-Hill]

You're trying to solve the wrong problem. You need to make MySet into a sufficiently rich interface so that union() can be implemented using methods of the interface. For example, if MySet had a "toArray()" method (and I'm not saying that's the best way to do it, just an easy way!) then union() could be implemented like

public MySet union(MySet other) {
    int[] otherData = other.toArray();
    MyArraySet result = new MyArraySet();
    for (int d: data)
        result.add(d);
    for (int m: arrElements)
        result.add(m);
    return result;
}

Instead of "toArray()", you might have a method "size()" and a method "get(int)" to allow a client to access each element of the set, or (better) implement something analogous to java.util.Iterator, but with int instead of Object.

[Derek Szpik]

OK, I will try that.

Since I have to declare sets as MySet s = new MyArraySet(); I thought that there would be a simple way to turn a set into MyArraySet. I do have a size() method, so I'll try making a get(int) method and working that way, thank you