Java - Using iterators with arrays

Question

I am new to the whole "iterator" concept in Java and need help with implementing it in my code. Here is the code:

class IteratorExample {

int tstArray [];

IteratorExample(){

}

public void addNum(int num){

   tstArray[0] = num; //And yes, I can only add one number at the moment, but it
                      is not what I want to focus on right now.
}


public Iterator<Integer> innerIterator(){
    return new methodIterator();
}

 class methodIterator implements Iterator<Integer> {
    public int index;
    private methodIterator(){
        index = 0;
    }

    public boolean hasNext(){
        return index < tstArray.length;

    }
    public Integer next(){
        return;
    }


  }    

public static void main(String[] args){
    IteratorExample sample = new IteratorExample();
  test(sample);
}

public static void test(IteratorExample arr){
 arr.addNum(1);
 system.out.print(arr);
}

}

This is the code written so far. I want to make it so I can add a number to an array using the addNum() method and then display it from main using system.print (and yes, I am aware that I need a toString method in order for the numbers to come up instead of the memory-address, that will be implemented later on, right now I am only focused on getting this to work.)

"And yes, I can only add one number at the moment, but it is not what I want to focus on right now." - Actually, it is what you should be focusing on. 'Cos it includes infrastructure that the iterator needs. — Stephen C
– Stephen C, Commented Oct 2, 2015 at 23:27
Why are you trying to add an iterator to a non-collection type? — Elliott Frisch
– Elliott Frisch, Commented Oct 2, 2015 at 23:27
I am trying to compare the run speed between an array and and arraylist with iterators. It is unconventional(and may I add not practical?) but that is the real reason. — tomSurge
– tomSurge, Commented Oct 2, 2015 at 23:29

Paul Boddington · Accepted Answer · 2015-10-02 23:46:16Z

2

To make the Iterator work, the next() method could be

public Integer next(){
    return tstArray[index++];
}

This throws an ArrayIndexOutOfBoundsException if the index is too large, whereas the specification for Iterator says it should throw a NoSuchElementException. In order to do it properly you could write

public Integer next(){
    if (index < tstArray.length)
        return tstArray[index++];
    throw new NoSuchElementException();
}

edited Oct 2, 2015 at 23:46

answered Oct 2, 2015 at 23:40

Paul Boddington

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