List

1. What is a List?

List is an interface in the Collection Framework that represents an ordered group of elements, where duplicate values are allowed, and each element has a specific position (index), just like an array.

2. Why is it used?

List is used whenever the order of elements matters, and duplicates are acceptable — like maintaining a list of items in a shopping cart, where the same item could appear more than once.

3. Real-Life Example

Think of a to-do list written on paper. Items are in a specific order, and you could accidentally write the same task twice — both are perfectly fine for a List.

4. Syntax

java
List<DataType> listName = new ArrayList<>(); // or LinkedList, Vector, etc.

5. Example Program

java
import java.util.List;
import java.util.ArrayList;

public class ListDemo {
    public static void main(String[] args) {
        List<String> tasks = new ArrayList<>();
        tasks.add("Read");
        tasks.add("Write");
        tasks.add("Read"); // duplicate allowed
        System.out.println(tasks);
    }
}

Output:

[Read, Write, Read]

6. Key Points to Remember

• List maintains insertion order and allows duplicate elements.
• List is an interface — you must use an implementing class like ArrayList, LinkedList, or Vector to actually create one.
• Elements in a List are accessed using a zero-based index, just like arrays.