Arrays aur ArrayList

Ek Java array ka size creation ke waqt fixed set hota hai aur grow karne ka koi built-in tarika nahi hota — array.length aapko woh size directly deta hai, kyunki C arrays ke ulat, ek Java array hamesha apni khud ki length jaanta hai.

public class Main {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5};
        System.out.println("numbers[2] = " + numbers[2]);
        System.out.println("length = " + numbers.length);
    }
}

numbers[2] = 3
length = 5

ArrayList

ArrayList Java ka primary growable collection hai — jab aap elements add karte ho to yeh apna khud ka resizing manage karta hai, aur Java ke saare generic collections ki tarah, yeh sirf reference types hold karta hai, isliye ek ArrayList<Integer> directly primitive int values ke bajaye boxed Integer objects store karta hai.

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        ArrayList<Integer> numbers = new ArrayList<>();
        numbers.add(1);
        numbers.add(2);
        numbers.add(3);
        numbers.add(4);
        System.out.println(numbers);
        System.out.println("size = " + numbers.size());
    }
}

[1, 2, 3, 4]
size = 4

Aage: strings — String immutability, concatenation, aur == aur .equals() mein farq.