Java Language Collections Creating your own Iterable structure for use with Iterator or for-each loop.
Example
To ensure that our collection can be iterated using iterator or for-each loop, we have to take care of following steps:
- The stuff we want to iterate upon has to be
Iterableand exposeiterator(). - Design a
java.util.Iteratorby overridinghasNext(),next()andremove().
I have added a simple generic linked list implementation below that uses above entities to make the linked list iterable.
package org.algorithms.linkedlist;
import java.util.Iterator;
import java.util.NoSuchElementException;
public class LinkedList<T> implements Iterable<T> {
Node<T> head, current;
private static class Node<T> {
T data;
Node<T> next;
Node(T data) {
this.data = data;
}
}
public LinkedList(T data) {
head = new Node<>(data);
}
public Iterator<T> iterator() {
return new LinkedListIterator();
}
private class LinkedListIterator implements Iterator<T> {
Node<T> node = head;
@Override
public boolean hasNext() {
return node != null;
}
@Override
public T next() {
if (!hasNext())
throw new NoSuchElementException();
Node<T> prevNode = node;
node = node.next;
return prevNode.data;
}
@Override
public void remove() {
throw new UnsupportedOperationException("Removal logic not implemented.");
}
}
public void add(T data) {
Node current = head;
while (current.next != null)
current = current.next;
current.next = new Node<>(data);
}
}
class App {
public static void main(String[] args) {
LinkedList<Integer> list = new LinkedList<>(1);
list.add(2);
list.add(4);
list.add(3);
//Test #1
System.out.println("using Iterator:");
Iterator<Integer> itr = list.iterator();
while (itr.hasNext()) {
Integer i = itr.next();
System.out.print(i + " ");
}
//Test #2
System.out.println("\n\nusing for-each:");
for (Integer data : list) {
System.out.print(data + " ");
}
}
}
Output
using Iterator:
1 2 4 3
using for-each:
1 2 4 3
This will run in Java 7+. You can make it run on Java 5 and Java 6 also by substituting:
LinkedList<Integer> list = new LinkedList<>(1);
with
LinkedList<Integer> list = new LinkedList<Integer>(1);
or just any other version by incorporating the compatible changes.
