Modifying lists with ListIterator

Input/Output and Streams in Java

Alex Liu

Software Development Engineer

Iterator vs ListIterator

Comparison between Iterator and ListIterator

Sample ArrayList

import java.util.ArrayList;
public class SampleData {
    public static void main(String[] args) {
        ArrayList<String> names = new ArrayList<>();
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");
    }
}

[Alice, Bob, Charlie]

Traversing a list with ListIterator

// Import ListIterator class
import java.util.ListIterator;


// Create ListIterator object for sample list `names`
ListIterator<String> it = names.listIterator();
// Use .hasNext() and `.next()` to iterate the list and print line by line
while (it.hasNext()) {
    System.out.println(it.next());
}

Alice 
Bob 
Charlie

Moving backward with ListIterator

Use .previous() to move backward in the list

// Create ListIterator object for sample list `names`
ListIterator<String> it = names.listIterator(names.size());
// Use .hasPrevious() to check if the iterator reach the beginning of the list
while (it.hasPrevious()) {
    // Use .previous() to retrieve the element in reverse order
    System.out.println(it.previous());}

Print element in reserve order, output:

Charlie
Bob
Alice

Modifying elements during iteration

Using the .set() method

// Create ListIterator object for sample list names
ListIterator<String> it = names.listIterator();

// Iterate the list and modify element using .set()
while (it.hasNext()) {
    String name = it.next();
    if ("Bob".equals(name)) it.set("Bobby");
}

Updated names list:

[Alice, Bobby, Charlie]

Adding elements during iteration

Use .add() to add elements

ListIterator<String> it = names.listIterator();


// Iterate the list and insert element using .add()
while (it.hasNext()) {
    String name = it.next();
    if ("Charlie".equals(name)) it.add("David");
}

Updated names list:
```
[Alice, Bobby, Charlie, David]
```

Summary

ListIterator extends Iterator
- Supports both forward and backward traversal
- Allows modifying elements while iterating
Key Methods Recap
- .next()/.previous(): Navigate forward and backward
- .set(): Modify the current element
- .add(): Insert elements dynamically
- .remove(): Safely delete elements
- Works only on Lists (ArrayList, LinkedList, etc.)

Let's practice!

Input/Output and Streams in Java