Java ArrayList

A regular Java array has a fixed size: once you create it with room for five items, it stays that size forever. An ArrayList removes that limit. You can keep adding items and it grows automatically, and you can remove items and it shrinks. It stores objects, so it works with String, Integer, and your own classes, but not raw primitives like int directly.

import java.util.ArrayList;

public class Main {
  public static void main(String[] args) {
    ArrayList<String> fruits = new ArrayList<>();
    fruits.add("Apple");
    fruits.add("Banana");
    fruits.add("Cherry");

    System.out.println(fruits);          // [Apple, Banana, Cherry]
    System.out.println(fruits.get(1));   // Banana
    System.out.println(fruits.size());   // 3
  }
}

The angle brackets <String> are called generics. They tell the ArrayList what type of item it holds, so the compiler can stop you from accidentally adding the wrong type. The get method reads an item by its index, starting at 0, and size tells you how many items are in the list.

Changing and removing items

import java.util.ArrayList;

public class Main {
  public static void main(String[] args) {
    ArrayList<String> colors = new ArrayList<>();
    colors.add("Red");
    colors.add("Green");
    colors.add("Blue");

    colors.set(1, "Yellow");   // replace Green with Yellow
    colors.remove(0);          // remove Red

    for (String color : colors) {
      System.out.println(color);
    }
    // Output:
    // Yellow
    // Blue
  }
}

The enhanced for loop, sometimes called a for-each loop, is the cleanest way to visit every element. You can also use a classic for loop with an index when you need the position, for example for (int i = 0; i < colors.size(); i++).

• ArrayList is a resizable list that grows and shrinks automatically.
• Use generics like <String> to fix the element type.
• Common methods: add, get, set, remove, size, and clear.
• It stores objects, so use wrapper classes such as Integer for numbers.