Can you create a Java Iterator over a 2d array?

Question

Can you create a single Iterator that will step over all spaces in a 2d array?

• Brian Roach: What have you tried?
• Stephen C: @Brian - that is an excellent link!
• Brian Roach: Yeah - I saw someone use it on here in this fashion, and I've now adopted it. I think it explains the issue without being a rant or too harsh.
• Ali: What iteration order would you use? X,Y,X1,Y1,X2,Y2 etc.. or X,X1,X2... Y,Y1,Y2 etc...?
• rghome: This is actually quite a sensible question and quite hard to do. I would not expect an inexperienced programmer to be able to do it.

Answer 1

If you implement the Iterable interface, you can use a for-each loop. Related examples may be found here.

Answer 2

Yes, wrap the array in an object and make the object implement the iterator interface. So it can be done. I am not aware of any such iterator that ships with the Jdk.

Answer 3

Yes, it can be done, as @Scorpion says. In fact, the solution is probably pretty simple: no more than 10 lines of executable code ... if I correctly understand the problem.

No, there isn't a convenience method in the JDK to do this. And I'm not aware of one in any of the "commons" libraries. (Reason: this particular problem is too specialized to be useful to more than a handful of programmers.)

This should be a sufficient answer for you to go and implement the solution yourself.

---

Should I / we provide you a potted solution? IMO, no.

• StackOverflow is not a "we write your code for free" service.

• If you do it yourself you will learn more: read the excellent "What have you tried?" blog article.

(And even if someone did feel like writing the code for you, you didn't give a clear enough description of the problem to implement ... without making lots of guesses.)

Answer 4

I dont see the need to make a single iterator when invoking the two from the arrays works just fine as per example:

int 2dArray[][];
for(int 1dArray[]: 2dArray){
 for(int i: 1dArray){
 //do stuff
 }
}

Answer 5

import java.util.LinkedList;
import java.util.Queue;
public class TwoDIterator {
int[][] array;
int outerCursor;
int lastArrayLen;
int totalElems;
int tracker = 1;
Queue<Integer> myQueue = new LinkedList<>();
public TwoDIterator(int[][] arr) {
 this.array = arr;
 this.outerCursor = 0;
 for (int i = 0; i < arr.length; i++) {
 for (int j = 0; j < arr[i].length; j++) {
 totalElems += 1;
 }
 }
 for (int i = 0; i < array[0].length; i++) {
 myQueue.add(array[0][i]);
 }
}
public boolean hasNext() {
 return array.length > outerCursor && totalElems >= tracker;
}
public Integer next() {
 if (myQueue.isEmpty()) {
 outerCursor++;
 for (int i = 0; i < array[outerCursor].length; i++) {
 myQueue.add(array[outerCursor][i]);
 }
 if (!myQueue.isEmpty()) {
 tracker++;
 return myQueue.remove();
 }
 } else {
 tracker++;
 return myQueue.remove();
 }
 return -1;
}
public static void main(String[] args) {
 int[][] arr = { { 1, 2, 3 }, { 1, 3 }, { 1, 2, 5 } };
 TwoDIterator iter = new TwoDIterator(arr);
 while (iter.hasNext()) {
 System.out.println(iter.next());
 }
}
}