Java Arrays.sort() method takes 1D arrays, but I can pass a 2D array as well then why can't I do int[] a=b(where b is a 2D array)?

Question

I'm having difficulty understanding the concept that I can pass a 2D array to java's Arrays.sort() method.(I have seen the java docs, the sort method can take only 1D arrays)
But then when I try the following code I get error

int[][] b={{1,2},{2,3}};
int[] a=b;

But the following code works fine

int[][] temp = { { 1, 50, 5 }, { 2, 30, 8 }, { 3, 90, 6 },{ 4, 20, 7 }, { 5, 80, 9 }, };
Arrays.sort(temp, new Comparator<int[]>() {
@Override
public int compare(int[] o1, int[] o2) {
    return Integer.compare(o2[1], o1[1]);
}
});

Answer 1

Java doesn't have true 2D arrays. What it has is a 1D array of 1D arrays. This means you can pass int[][][] to Arrays.sort as long as you pass a comparator for int[][] elements.

e.g.

int[][][] a = { ... }
int[][] b = a[0];
int[] c = b[0];
int d = c[0];

You can also write

Object[] x = a; // as int[][] is an Object.
Object[] y = b; // as int[] is an Object.
Object[] z = c; // doesn't compile. as int is not an Object.