Implementing Iterator

[Harb]

Hello.
I'm trying to make a class that I want to be able to use in a "foreach" statement. My question is, how does the object know when to start over in a new iteration? (i.e. next time I want to iterate through the collection)

I'm using a counter with the next() method to keep track of which object it is currently on, but I'm unsure of which method is supposed to reset the counter to start over from the beginning.

[henry_78]

Hi,
First of all, Iterator is a java interface and it has methods to iterate on elements of collections.
Un can create your own iterator implementing that interface:
The methods of the interface are:
hasNext() : To know if there other elements left in the collection.
next() : Returns the next element.
remove() : To remove the current element from the collection(better not use that metthod).

U can read more about the Iterator in the java doc.
Bye.

[Harb]

Thanks for the reply, and sorry for not being very clear in my first post.

So far I have:

Code:

public class MyClass implements Iterable<AnotherClass>, Iterator<AnotherClass> {
count = 0;
AnotherClass[] collection;

public MyClass(){
}


//constructors and other stuff here
...


public Iterator<AnotherClass> iterator() {
    return this;
}

public boolean hasNext() {
    return count < collection.size();
}

public AnotherClass next() {
    if(count == collection.size()){
            throw new NoSuchElementException();
    }
    return collection[count];
    }

public void remove() {
    throw new UnsupportedOperationException();
}

And according to the example I've read on another site, this should work. What I don't understand though, is when/where should i reset the count variable? (I realize the class I've presented is pretty useless, I'm using it merely as an example) If I iterate through the collection once, the count variable will be incremented until it reaches the end of the collection. And if I want to iterate through it again, it seems to me I'll have a problem :P

[henry_78]

Hi,
In this implementation u have to increment 'count' when u invoke the next() method, this will help u to know when your collection is finished.
As u can see in your code, the hasNext() method verifies that
count < collection.size();
To iterate another time, u have to create another itaerator...or change your class adding more methods.
Bye.

[hardwired]

Seems like you would reset the count after the last element was sent out.

Code:

public AnotherClass next() {
    if(count == collection.size()){
            throw new NoSuchElementException();
    }
    if(count == collection.size()-1) {
        // last element being sent out.
        count = 0;
        return collection[collection.size()-1];
    }
    return collection[count];
}

[henry_78]

If u do like that, u wont even know when u reach the end of the collection.
When a n iterator reach the end of a collection it stops..it dosen't go back to the first element.
U should change only the next() method like that:

public AnotherClass next() {
if(count == collection.size() ){
throw new NoSuchElementException();
}
count++;
return collection[count];
}

[hardwired]

If u do like that, u wont even know when u reach the end of the collection.

Right.