Iterator type problem

[Jaime Caetano]

hey, well I've been over this school problem for two days, for other matter il try to ask laster
by now I decided to slice my big problem into little parts, sooo....

static Iterable<Boolean> getEquals (Collection<String> c1,
   Collection<String> c2, Comparator<String> cmp) {

        Iterator<String> it1 = c1.iterator();
        Iterator<String> it2 = c2.iterator();
        
        Collection<Boolean> result = new ArrayList<Boolean>();
        

        while (!it1.hasNext() && !it2.hasNext()) {

            if (cmp.compare(it1.next(), it2.next()) == 0) 
                result.add(true);
            else result.add(false);
 
        }
   
        Iterable<Boolean> iter = new Iterable<Boolean>(){
  
            public Iterator<Boolean> iterator() {
                return new Iterator<Boolean>(){
                    private int c = 0;
                    
                    public boolean hasNext() {
                        return c < size;
                    }
                                
                    public Boolean next() {
                        return result.get(c++);
                    }
 
                    public void remove() {
                        throw new UnsupportedOperationException(
                           "Not supported yet.");
                    }            
                };                
            } 
        };
        
     
        return iter;
        

    }


public static void main(String [] args){

boolean o = getEquals(c1,c2,cmp).next();


}

when I write that expression on my main method, i get a message saying:

incompatible types, object can not be converted to boolean,

this is getting me confused, cause the method getEquals() returns a boolean iterator

and then im simply using next method over getEquals(), I suppose that should be a boolean,

what is going on people?


open to sugestion brothers,

thanks

[Jeanne Boyarsky]

Can you show what you put for c1, c2 and cmp? I picked the following and the code compiled for me

List<String> c1 = new ArrayList<>();
List<String> c2 = new ArrayList<>();
Comparator<String> cmp = new Comparator<String>() {
	
	@Override
	public int compare(String o1, String o2) {
		return 0;
	}
};

Just curious - why don't you just return the boolean directly? What is the purpose of returning an iterator with a single boolean object?

And good instinct on splitting the problem in smaller parts. That really is a good way to program and problem solve.

[Jaime Caetano]

damm! I've made a mistake, the method type is Iterable<Boolean> not Iterator<Boolean>

i can now return an Iterable,

the goal of the exercice is receiving two collections c1, c2... and a comparator cmp..(lexicographical)

Comparator cmp = new Comparator<String>() {
            public int compare(String c1, String c2) {
                return c1.compareTo(c2);
            }
        };

execute on the main method this expression:


for (boolean o : getEquals(c1, c2, cmp))
System.out.println(o);


which will return booleans, according to the comparator result

still getting the same problem tho :s

[Jeanne Boyarsky]

Can you show your new getEquals method implementation?

[Winston Gutkowski]

Jaime Caetano wrote:hey, well I've been over this school problem for two days...

OK, well there's quite a lot of stuff going on here, so a good practise is usually to write out what needs to be done, in detail, and in English (or your native language) first - before you write a single line of code.

However, just from what I see:

1. Your loop continues while both collections have more elements, which suggests that your Iterable<Boolean> will be the same length as the shorter Collection. It's not necessarily an error, but it might be worth documenting why you chose this approach.

2. You're using a Comparator and compare() to return the result of something for a method called getEquals(). Again, not necessarily a problem, but it might be worth documenting why; otherwise it begs the question: Why don't you just use equals()?

3. (A very minor performance thing) You're adding booleans, which have to be boxed to Booleans for your output Iterable. If you wrote

if (cmp.compare(it1.next(), it2.next()) == 0)
   result.add(Boolean.TRUE);
else
   result.add(Boolean.FALSE);

instead, your code would probably run faster. In this case you'll probably never notice the difference, but it's worth bearing in mind; particularly if multiple boxing/unboxing conversions get involved.

HIH

Winston

PS: Please don't edit your posts after the fact if you're asking questions about code you've posted, because it tends to make nonsense of the replies you get. Thanks.

[Jaime Caetano]

hey Winston,

thanks a lot for the tips, I really apreciatte your attention,

this exercice is academic, they want me to understand what is a comparator, anonimous class, collections, iterators all together,

thats the Bolonha system in Portugal, but that's other story which im not willing to complain about.

I might need to go to the root of my problem, interfaces.

so I will create another post,

thank you, Jaime