Cursor In Java

In Java, the term cursor typically refers to objects used to traverse or iterate over elements in a collection, such as Iterator, ListIterator, and Enumeration. These are called cursor interfaces.

🔹 Types of Cursors in Java

Cursor Type	Introduced In	Applicable Collections	Traversal	Modifications	Direction
`Enumeration`	JDK 1.0	Legacy classes (`Vector`, `Hashtable`)	Read-only	No	Forward
`Iterator`	JDK 1.2	All `Collection` types	Yes	Yes (`remove()`)	Forward
`ListIterator`	JDK 1.2	Only `List` types	Yes	Yes (`add()`, `remove()`, `set()`)	Forward and Backward

🔹 1. Enumeration (Legacy)

import java.util.*;

public class EnumerationExample {
    public static void main(String[] args) {
        Vector<String> vector = new Vector<>();
        vector.add("A");
        vector.add("B");

        Enumeration<String> enumeration = vector.elements();
        while (enumeration.hasMoreElements()) {
            System.out.println(enumeration.nextElement());
        }
    }
}

✅ Read-only and forward-only

🔹 2. Iterator (Modern Standard)

import java.util.*;

public class IteratorExample {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>(List.of("Apple", "Banana", "Cherry"));
        Iterator<String> iterator = list.iterator();

        while (iterator.hasNext()) {
            String fruit = iterator.next();
            if (fruit.equals("Banana")) {
                iterator.remove(); // Safe removal
            } else {
                System.out.println(fruit);
            }
        }

        System.out.println("Updated List: " + list);
    }
}

✅ Can remove elements during iteration.
❌ Cannot move backward.

🔹 3. ListIterator (Advanced for Lists)

import java.util.*;

public class ListIteratorExample {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>(List.of("One", "Two", "Three"));
        ListIterator<String> listIterator = list.listIterator();

        // Forward traversal
        while (listIterator.hasNext()) {
            String value = listIterator.next();
            if (value.equals("Two")) {
                listIterator.set("TWO"); // Modify the element
            }
        }

        // Backward traversal
        System.out.println("Reverse:");
        while (listIterator.hasPrevious()) {
            System.out.println(listIterator.previous());
        }

        System.out.println("Updated List: " + list);
    }
}

✅ Supports:

Forward & backward iteration
Add, remove, and update

🔹 Cursor Usage Summary

Operation	Enumeration	Iterator	ListIterator
Forward traversal	✅	✅	✅
Backward traversal	❌	❌	✅
Element removal	❌	✅	✅
Element addition	❌	❌	✅
Element modification	❌	❌	✅
Applicable to List	✅	✅	✅
Applicable to Set	❌	✅	❌

🔹 Real-World Tip

Use Iterator when working with general collections like Set, Queue.
Use ListIterator only when working with List and you need bidirectional navigation or modification.
Avoid using Enumeration in new code — it's outdated.