Java 3D array assign values

static String[][][] School= new String[1000][20][5]; 

Consider figure which has 3 Dimension.

So when you insert School[0][0][0]="A1" it means you have entered element at 0,0,0 position.

From 0,0,0 this will move upto the position 1000,20,5.

You can insert like this But you have so many elements.

School[0][0][0]="A1"
School[0][0][1]="A2"
School[0][0][2]="A3"
.....
School[0][1][0]="B1"
School[0][1][1]="B2"
School[0][1][2]="B3"
......

In 3D array elements look like

int[3][4][2] array3D
// means Three (4x2) 2 Dimensional Arrays 

 int[4][2]
 //means Four 1 dimensional arrays.

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Now how to add elements in 3D array?

At Start you can directly use

int[][][] threeDArray = 
    {  { {1,   2,  3}, { 4,  5,  6}, { 7,  8,  9} },
       { {10, 11, 12}, {13, 14, 15}, {16, 17, 18} },
       { {19, 20, 21}, {22, 23, 24}, {25, 26, 27} } };

This is very tedious task in your case as you want to insert details at every position. As you have 1000 records.

Your array will have elements like this

NOTE:It's not recommended to use 3D array for this purpose.

Suggestion:Declare a class with three Strings create constructor with this three parameters and put getter and setters to get and set values via Objects

I will suggest instead of using a 3D array, you shall create a Student Class that will hold all the information for a student and A Class for SchoolClass that will hold a list of students in the class and name of class and you can maintain an Array of SchoolClass to serve the purpose.

This way you will be able to manage it better.

Hope this helps