Write a Java program to demonstrate the use of Iterator and ListIterator on a collection.

Answer

Iterator and ListIterator in Java

Iterator — Forward Traversal Only

Java

import java.util.*;

public class IteratorDemo {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>(
            Arrays.asList("Selenium", "TestNG", "Cucumber", "Maven", "Jenkins")
        );

        // Get Iterator
        Iterator<String> it = list.iterator();

        System.out.println("Using Iterator (forward):");
        while (it.hasNext()) {
            String tool = it.next();
            System.out.println(tool);

            // Safe removal during iteration (avoids ConcurrentModificationException)
            if (tool.equals("Maven")) {
                it.remove();  // removes "Maven" safely
            }
        }

        System.out.println("After removing Maven: " + list);
    }
}

Output

CODE

Using Iterator (forward):
Selenium
TestNG
Cucumber
Maven
Jenkins
After removing Maven: [Selenium, TestNG, Cucumber, Jenkins]

ListIterator — Bidirectional + Modify

Java

ArrayList<String> list = new ArrayList<>(
    Arrays.asList("Chrome", "Firefox", "Edge", "Safari")
);

ListIterator<String> lit = list.listIterator();

// Forward traversal
System.out.println("Forward:");
while (lit.hasNext()) {
    System.out.println(lit.nextIndex() + ": " + lit.next());
}

// Backward traversal
System.out.println("Backward:");
while (lit.hasPrevious()) {
    System.out.println(lit.previousIndex() + ": " + lit.previous());
}

// Modify during iteration
ListIterator<String> lit2 = list.listIterator();
while (lit2.hasNext()) {
    String browser = lit2.next();
    lit2.set(browser + "-Driver");   // replace each element
}
System.out.println("Modified: " + list);
// → [Chrome-Driver, Firefox-Driver, Edge-Driver, Safari-Driver]

Iterator vs ListIterator vs For-Each

Feature	Iterator	ListIterator	For-Each
Direction	Forward only	Both	Forward only
Remove during loop	Yes (it.remove())	Yes	NO (ConcurrentModificationException)
Add during loop	No	Yes (lit.add())	No
Index access	No	Yes	No
Works on	Any Collection	List only	Any Iterable

Automation Testing Relevance

Java

// Safely remove stale elements from list
List<WebElement> elements = driver.findElements(By.css(".item"));
Iterator<WebElement> it = elements.iterator();
while (it.hasNext()) {
    WebElement el = it.next();
    if (!el.isDisplayed()) {
        it.remove();  // remove elements that are not visible
    }
}