Code of the snake Matrix

The snake matrix is a special matrix, but it is not difficult to use a program to implement it as long as you have mastered the laws of coordinates.
The following is the snake Matrix I implemented using Java:
When N = 4
Output:
1 2 6 7
3 5 8 13
4 9 12 14
10 11 15 16

The source code is implemented as follows:

Import javax. Swing. joptionpane;
Public class test
{
Public static void main (string [] ARGs)
{
String STR;
Final int max = 10;
Int input;
Int D, I, j, M;
Int A [] [] = new int [10] [10];
STR = joptionpane. showinputdialog ("input :");
Input = integer. parseint (STR );
If (input> 0 & input <max)
{
I = 1;
J = 1;
M = 1;
D = 1;
Do
{
A [J] = m;
Switch (d)
{
Case 1: J ++; if (I = 1) d = 2; else d = 4; break;
Case 2: I ++; j --; if (I = input) d = 1;
Else if (j = 1) d = 3; break;
Case 3: I ++; If (j = input) d = 2; else d = 4; break;

Case 4: J ++; I --; If (j = input) d = 3; else if (I = 1) d = 1; break;

}
M ++;
} While (M <= input * input );
System. Out. println ("output :");
System. Out. println ();
For (I = 1; I <= input; I ++)
{
For (j = 1; j <= input; j ++)
{System. Out. Print ("" + A [J]);}
System. Out. println ();
}
}
Else
System. Out. println ("the number of inputs is invalid. It must be 1 ~ Between 10! ");

}

}