Difference between Iterator and ListIterator in Java

💡 Concept: Iterator vs ListIterator

Iterator and ListIterator are interfaces used to traverse collections in Java, with ListIterator offering bidirectional traversal.

📘 Quick Intro

Iterator allows forward-only traversal, while ListIterator supports forward and backward traversal and element modification.

🧠 Analogy

Think of Iterator as a one-way street allowing cars only forward movement, while ListIterator is a two-way street allowing movement in both directions.

🔧 Technical Explanation

Iterator works with all Collection types; ListIterator works only with List implementations.
Iterator supports methods: hasNext(), next(), and remove().
ListIterator supports hasNext(), next(), hasPrevious(), previous(), add(), set(), and remove().
ListIterator allows modification during traversal; Iterator allows only removal.
ListIterator provides index information; Iterator does not.

🎯 Use Cases

✅ Use Iterator for simple forward traversal.
✅ Use ListIterator for complex bidirectional traversal and modification.
✅ Use ListIterator when index information is needed during iteration.

💻 Code Example: Iterator vs ListIterator


import java.util.*;

public class IteratorExample {
    public static void main(String[] args) {
        List list = new ArrayList<>(Arrays.asList("Java", "Collections", "Framework"));

        Iterator iterator = list.iterator();
        System.out.println("Iterator traversal:");
        while(iterator.hasNext()) {
            System.out.println(iterator.next());
        }

        ListIterator listIterator = list.listIterator();
        System.out.println("\nListIterator traversal:");
        while(listIterator.hasNext()) {
            System.out.println(listIterator.next());
        }
        System.out.println("Backward traversal:");
        while(listIterator.hasPrevious()) {
            System.out.println(listIterator.previous());
        }
    }
}

❓ Interview Q&A

Q1: Which interface allows bidirectional traversal?
A: ListIterator.

Q2: Does Iterator support element addition?
A: No.

Q3: Can ListIterator modify elements?
A: Yes.

Q4: Which collections support Iterator?
A: All Collection implementations.

Q5: Is ListIterator limited to Lists?
A: Yes.

Q6: Methods unique to ListIterator?
A: hasPrevious(), previous(), add(), set().

Q7: Can Iterator remove elements?
A: Yes.

Q8: Which is more feature-rich?
A: ListIterator.

Q9: Can Iterator traverse backwards?
A: No.

Q10: Which interface provides index info?
A: ListIterator.

📝 MCQs

Q1. Which interface allows bidirectional traversal?

Iterator
ListIterator
Both
None

Q2. Does Iterator support element addition?

Yes
No
Sometimes
Always

Q3. Can ListIterator modify elements?

No
Yes
Sometimes
Never

Q4. Which collections support Iterator?

Only Lists
Only Sets
All Collection implementations
None

Q5. Is ListIterator limited to Lists?

No
Yes
Sometimes
No difference

Q6. Methods unique to ListIterator?

next(), hasNext()
hasPrevious(), previous(), add(), set()
remove()
All of above

Q7. Can Iterator remove elements?

No
Yes
Sometimes
Never

Q8. Which is more feature-rich?

Iterator
ListIterator
Both equal
None

Q9. Can Iterator traverse backwards?

Yes
No
Sometimes
Always

Q10. Which interface provides index info?

Iterator
ListIterator
Both
None

💡 Bonus Insight

ListIterator is a powerful extension to Iterator providing bidirectional traversal and modification capabilities.

📄 PDF Download

Need a handy summary for your notes? Download this topic as a PDF!

📄 PDF Download Coming Soon