3-Dimensional Array in Java One Page.md

3-Dimensional Array in Java — ONE PAGE

1. What is a 3-Dimensional Array?

A 3-Dimensional Array stores data using three indexes.

Think of it as:

Layers → Rows → Columns

Syntax:

int[][][] a;

Access an element:

a[layer][row][column]

Example

int[][][] a = { { {10, 20, 30}, {40, 50, 60} }, { {70, 80, 90}, {100, 110, 120} } };

Visualize:

Layer 0 ┌────┬────┬────┐ │ 10 │ 20 │ 30 │ ├────┼────┼────┤ │ 40 │ 50 │ 60 │ └────┴────┴────┘

Layer 1 ┌────┬────┬────┐ │ 70 │ 80 │ 90 │ ├────┼────┼────┤ │100 │110 │120 │ └────┴────┴────┘

---

2. Three Indexes

The golden rule:

a[layer][row][column] ↓ ↓ ↓ 1 2 3

For example:

System.out.println(a[1][0][2]);

Means:

Layer 1 ↓ Row 0 ↓ Column 2 ↓ 90

Output:

90

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3. Declaration

int[][][] a;

Other valid forms:

int a[][][]; int[] a[][];

Preferred:

int[][][] a;

---

4. Creation

int[][][] a = new int[2][3][4];

Meaning:

2 → layers 3 → rows per layer 4 → columns/elements per row

Total elements:

2 × 3 × 4 = 24

---

5. Direct Initialization

int[][][] a = { { {1, 2}, {3, 4} }, { {5, 6}, {7, 8} } };

Structure:

Layer 0 Layer 1

1 2 5 6 3 4 7 8

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6. Traversing a 3-D Array

Because there are three dimensions, we generally need three nested loops:

for (int i = 0; i < a.length; i++) {

for (int j = 0; j < a[i].length; j++) {

    for (int k = 0; k < a[i][j].length; k++) {

        System.out.print(a[i][j][k] + " ");
    }

    System.out.println();
}

System.out.println();

}

Remember:

i → Layer j → Row k → Column

Therefore:

a[i][j][k]

means:

Layer → Row → Column

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7. Understanding length

For:

int[][][] a = new int[2][3][4];

Number of layers

a.length

→ 2

Number of rows in layer i

a[i].length

→ 3

Number of columns in row j of layer i

a[i][j].length

→ 4

So:

a.length ↓ Layers

a[i].length ↓ Rows

a[i][j].length ↓ Columns

---

8. Complete Example

class ThreeDArray {

public static void main(String[] args) {

    int[][][] a = {
        {
            {10, 20},
            {30, 40}
        },
        {
            {50, 60},
            {70, 80}
        }
    };

    for (int i = 0; i < a.length; i++) {

        for (int j = 0; j < a[i].length; j++) {

            for (int k = 0; k < a[i][j].length; k++) {

                System.out.print(a[i][j][k] + " ");
            }

            System.out.println();
        }

        System.out.println();
    }
}

}

Output:

10 20 30 40

50 60 70 80

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⭐ 3-D Array Memory Map

3-D ARRAY ↓ int[][][] a ↓ ┌──────┴──────┐ ↓ ↓ Layer 0 Layer 1 ↓ ↓ Rows Rows ↓ ↓ Columns Columns

The most important formula:

a[i][j][k]

i → Layer j → Row k → Column

One-line definition:

A 3-Dimensional Array in Java is an array of 2-Dimensional arrays used to store data in layers, rows, and columns.