Java Collections: Everything You Need to Know About the List Interface

1.List Interface :

The List interface is part of java.util and extends the Collection interface. It represents an ordered sequence of elements — you can access any element by its position (index).

• It is Ordered
• It Allows duplicates
• Index-based access

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

List<String> fruits = new ArrayList<>();
fruits.add("Apple");
fruits.add("Banana");
fruits.add("Mango");
System.out.println(fruits.get(0)); // Output: Apple

The 2 main implementations :

Arraylist:

• Elements sit side-by-side in memory. Jump to any index instantly — like numbered boxes in a row.
• It stores elements in a contiguous block of memory, so get(5) jumps straight to position 5 — like page numbers in a book. This is called O(1) or "constant time."

-When you use ArrayList :

• You read or access elements often
• You mostly add to the end of the list
• Memory efficiency matters
• You need to iterate in order

Linkedlist:

• Each node holds the value + a pointer to next. Scattered in memory must walk the chain to find an element.

• Each element is a node that holds a pointer to the next. Inserting means just rewiring two pointers — no shifting needed. ArrayList, on the other hand, has to push every element after the insertion point one slot over.

-When you use Linkedlist :

• You insert/delete in the middle often
• You need a Queue or Deque structure
• List size changes frequently
• You process from both ends

Common List methods :

1.Add() — insert elements :

fruits.add("Grapes");           // Adds to end
fruits.add(1, "Cherry");      // Adds at index 1

2.get() & size() — access & count :

String first = fruits.get(0);  // "Apple"
int total = fruits.size();      // Total items

3.remove() — delete elements :

fruits.remove("Banana");       // Remove by value
fruits.remove(0);              // Remove by index