Enumeration in Java

In Java, Enumeration is a legacy interface used to traverse (iterate) through legacy collection classes like Vector, Hashtable, Stack, and Properties. It was introduced in JDK 1.0, before the modern Iterator interface was added in JDK 1.2.

🔹 Declaration of Enumeration Interface

public interface Enumeration<E> {
    boolean hasMoreElements();  // Checks if more elements exist
    E nextElement();            // Returns the next element
}

🔹 Common Use Cases

Enumeration is typically used with legacy collections such as:

Vector
Stack
Hashtable
Properties

🔹 Example: Enumeration with Vector

import java.util.*;

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

        Enumeration<String> enumeration = vector.elements();

        while (enumeration.hasMoreElements()) {
            System.out.println(enumeration.nextElement());
        }
    }
}

✅ Output:

Apple
Banana
Cherry

🔹 Limitations of Enumeration

Limitation	Description
Read-only	Cannot add or remove elements
Forward-only traversal	No support for backward movement
Legacy interface	Use `Iterator`/`ListIterator` for modern collections
No fail-fast behavior	Doesn't throw exceptions on concurrent modification

🔹 Enumeration vs Iterator

Feature	Enumeration	Iterator
Introduced in	JDK 1.0	JDK 1.2
Applicable to	Legacy classes only	All `Collection` types
Remove support	❌ Not supported	✅ Supported
Direction	Forward only	Forward only (Iterator), both with `ListIterator`
Safety	Not fail-fast	Fail-fast

🔹 Where Is Enumeration Still Used?

Even though it's outdated, you may still encounter it:

In legacy codebases.
With certain classes like Properties, ResourceBundle, or ClassLoader.
When using APIs that return Enumeration (e.g., ClassLoader.getResources()).

🔹 Modern Alternative: Iterator

If you're using modern List, Set, or Map, prefer:

Iterator<String> it = list.iterator();
while (it.hasNext()) {
    System.out.println(it.next());
}

✅ Summary

Enumeration is simple but limited.
Best used with legacy collections.
For modern code, use Iterator or ListIterator.

Would you like an example using Enumeration with a Hashtable or Properties file?

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