int[][] a = new int[2][3];
a[0][1] = 10;
System.out.println(a[1][0]);

int[][] a = {
    {1, 2, 3},
    {4, 5, 6}
};
int[] row = a[0];
row[1] = 100;
System.out.println(a[0][1]);

int[][] arr = new int[3][];

System.out.println(arr[0]); // null

arr[0] = new int[2];
arr[1] = new int[4];
arr[2] = new int[3];

arr[1][2] = 10;
System.out.println(arr[1][2]); // 10

arr.length       // количество ссылок на строки
arr[1].length    // длина второй строки

int[][] data = new int[3][];
data[0][0] = 5; // ошибка: data[0] == null

public class Main {
    static void print(long value) {
        System.out.println("long");
    }

    static void print(Integer value) {
        System.out.println("Integer");
    }

    public static void main(String[] args) {
        print(10);
    }
}

import java.util.Arrays;
class Main {
    static void change(int[] array) {
        array[0] = 10;
        array = new int[]{20, 30};
    }

    public static void main(String[] args) {
        int[] numbers = {1, 2};
        change(numbers);
        System.out.println(Arrays.toString(numbers));
    }
}

class Main {
    static void show(String value) {
        System.out.println("String");
    }

    static void show(Integer value) {
        System.out.println("Integer");
    }

    public static void main(String[] args) {
        show(null);
    }
}