1. List Interface

• List is an interface in Java, part of the java.util package.

• It represents a collection of elements that are ordered and allow duplicates.

• Since it's an interface, it cannot be instantiated directly. Instead, it is implemented by classes like ArrayList, LinkedList, etc.

2. ArrayList Class

• ArrayList is a class that implements the List interface.

• It is a resizable array that can dynamically grow or shrink.

• Elements in an ArrayList are stored in a contiguous memory location, making it efficient for random access.

Key Differences

Examples

Using ArrayList Directly

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        ArrayList<String> names = new ArrayList<>(); // Instantiate ArrayList
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");
        System.out.println(names); // Output: [Alice, Bob, Charlie]
    }
}

Using List for Flexibility

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

public class Main {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>(); // Instantiate using List reference
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");
        System.out.println(names); // Output: [Alice, Bob, Charlie]
    }
}

• You can easily switch to another implementation, like LinkedList, without changing much code:

import java.util.List;
import java.util.LinkedList;

public class Main {
    public static void main(String[] args) {
        List<String> names = new LinkedList<>(); // Switched to LinkedList
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");
        System.out.println(names); // Output: [Alice, Bob, Charlie]
    }
}

Choosing Between List and ArrayList

1. Use List when:
• You want to write generic code and allow switching implementations (e.g., LinkedList, ArrayList, Vector).
• You prefer flexibility and abstraction over implementation specifics.

2. Use ArrayList when:
• You specifically need a resizable array with random access.
• You are certain that ArrayList meets your performance requirements for your use case.

Summary

• Use List for abstraction and flexibility.

• Use ArrayList for a specific implementation with dynamic resizing and fast random access.