CODEWITHSUNDEEP
javaarraysloopsiterator
Developer Marius Žilėnas
Developer Marius Žilėnas

Reputation: 6119

Looping data structure in Java

Is there an Iterator to loop over data structure in cycles?

Let's say there is an array:

int[] arr = {-1,5,7,-1,-1,-1}

I want to find index of first non -1 value from this array and starting to search from the random position (idx = random.nextInt(arr.length)). For example idx = 4;

So first check if arr[4] == -1, then if arr[5] == -1 and so on. If the end of the array reached then start from 0 position and continue until non -1 found. It is guaranteed that there will be at least one value not equal to -1 in the array.

This can be done so:

int idx = -1;
for (int i = random.nextInt(arr.length); ; i++) {
   if (i == arr.length) {
        /** start over */
        i = 0;
   }
   if (-1 != arr[i]) {
       idx = i;
       break;
   }
}

Or so:

int idx = -1;
int i   = random.nextInt(arr.length);

do {
   if (-1 != arr[i]) {
      idx = i;
   }      
   i == arr.length ? i=0 : i++;
} while (-1 == idx);

Is there an Iterator, that supports cycling (call next() , if the end of array reached then automatically start from 0)?

Limitations: 1) efficiency is not considered; 2) standard Java API is preferred.

Upvotes: 1

Views: 2255

Answers (3)

Vineet Kosaraju
Vineet Kosaraju

Reputation: 5860

I believe there is no such circular Iterator that will automatically go to the beginning of the array once the end has been reached. I have created one below (not tested, and design is flawed), which requires an entirely new class of code, and is much longer than your short for/while loops.

public class MyCircularIterator<E> implements Iterator<E> {
    private List<E> list;
    private int pos;

    public MyCircularIterator(List<E> list) {
        this(list, 0);
    }

    public MyCircularIterator(List<E> list, int start) {
        this.list = list;
        pos = start;
    }

    public boolean hasNext() {
        if(list.get(pos) != -1) return false;
            return true;
    }

    public E next() {
        if(hasNext()) {
            E obj = list.get(pos);
            pos = (pos + 1) % list.size();
            return obj;
        }
    }

    public void remove() {
         list.remove(this.nextIndex); 
    }
}

Upvotes: 1

Pulah Nandha
Pulah Nandha

Reputation: 774

in java API there is no such api which satisfy your problem but you can made it by your own.

what you can do is use List to create LinkedList. to solve your problem.

you can extend List to your class (CircularLinkedList extends List) & then override method hasNext() & getNext() thats all you need.

Upvotes: 2

Ted Hopp
Ted Hopp

Reputation: 234847

I don't think there are any iterators that let you know the index of the element as you call next(), so you'd have to keep track of the current index separately. You might be able to build up a "wrap-around" iterator using Guava's Iterators.concat (or some other third-party class) to concatenate an iterator over the trailing part of the array with an iterator over the leading part. However, I think the code is likely to be more complex than a simple for loop or two.

Upvotes: 1

Related Questions