Guidetoiterator (#3368)

* Added code for iterator

* missing imports..

core-java/src/main/java/com/baeldung/iteratorguide/IteratorGuide.java

@@ -0,0 +1,39 @@
+package com.baeldung.iteratorguide;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.ListIterator;
+
+public class IteratorGuide {
+    
+    public static void main(String[] args) {
+        List<String> items = new ArrayList<>();
+        items.add("ONE");
+        items.add("TWO");
+        items.add("THREE");
+        Iterator<String> iter = items.iterator();
+        while (iter.hasNext()) {
+                String next = iter.next();
+                System.out.println(next);
+                iter.remove();
+        }
+        ListIterator<String> listIterator = items.listIterator();
+        while(listIterator.hasNext()) {
+            String nextWithIndex = items.get(listIterator.nextIndex());
+            String next = listIterator.next();
+            if( "ONE".equals(next)) {
+                listIterator.set("SWAPPED");
+            }
+        }
+        listIterator.add("FOUR");
+        while(listIterator.hasPrevious()) {
+            String previousWithIndex = items.get(listIterator.previousIndex());
+            String previous = listIterator.previous();
+            System.out.println(previous);
+        }
+        listIterator.forEachRemaining(e -> {
+            System.out.println(e);
+        });
+    }
+}