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Multi Dimensional Arrays

✔ It is an Array of Arrays.

TypeDescription
Single Dimensional ArrayCollection of actual values
Two Dimensional ArrayCollection of single dimensional arrays
Three Dimensional ArrayCollection of 2-D arrays

2.10.5 Two Dimensional Arrays

✔ Two Dimensional Arrays can be called as 2-D array.

2.10.5.1 Array Declaration​

Syntax​

[modifiers]<dataType> <refVarName>[][];
[modifiers]<dataType> [][]<refVarName>;
[modifiers]<dataType> [][]<refVarName>;
[modifiers]<dataType> []<refVarName>[];
[modifiers]<dataType> [] <refVarName>[];

Examples​

int arr[][];

int[][] arr;

String[] names[];

2.10.5.2 Array Construction​

Syntax​

<refVarName>=new <dataType>[<size1>][<size2>];

Explanation​

  • <size1> → number of arrays (rows)
  • <size2> → number of elements in each array (columns)

Examples​

arr=new int[3][2];
names=new String[4][3];

💡 Quick Understanding​

  • 2D array = array of arrays
  • Think like a table (rows × columns)
  • First size → rows
  • Second size → columns

2.10.5.3 Array Initialization

✔ You can initialize array elements with your own value using index representation.

int arr[][];
arr=new int[3][2];

✔ Explanation​

Here we are creating 3 arrays, each with size 2, and these three array addresses will be stored in the main array.

Default Values (before initialization)​

arr[0][0] -> Represents the 1st element of 1st array which contains value 0
arr[0][1] -> Represents the 2nd element of 1st array which contains value 0

arr[1][0] -> Represents the 1st element of 2nd array which contains value 0
arr[1][1] -> Represents the 2nd element of 2nd array which contains value 0

arr[2][0] -> Represents the 1st element of 3rd array which contains value 0
arr[2][1] -> Represents the 2nd element of 3rd array which contains value 0

✔ Initializing Values​

arr[0][0]=10;
arr[0][1]=20;

arr[1][0]=30;
arr[1][1]=40;

arr[2][0]=50;
arr[2][1]=60;

✔ Accessing the Elements After Initialization​

arr[0][0] -> Represents the 1st element of 1st array which contains value 10
arr[0][1] -> Represents the 2nd element of 1st array which contains value 20

arr[1][0] -> Represents the 1st element of 2nd array which contains value 30
arr[1][1] -> Represents the 2nd element of 2nd array which contains value 40

arr[2][0] -> Represents the 1st element of 3rd array which contains value 50
arr[2][1] -> Represents the 2nd element of 3rd array which contains value 60

💡 Quick Understanding​

  • 2D array = array of arrays
  • arr[i][j] → i = row, j = column
  • Default values → 0 (for int)
  • You can assign values manually using indexes

2.10.5.4 Array Declaration and Construction

Syntax​

[modifiers]<dataType> <refVarName>[][]=new <dataType>[<size1>][<size2>];
[modifiers]<dataType> [][]<refVarName>=new <dataType>[<size1>][<size2>];

Examples​

int arr[][] = new int[3][2];

int[][] arr = new int[3][2];

2.10.5.5 Array Declaration, Construction and Initialization

Syntax​

<dataType><refVarName>[][]= { {v1,v2,...}, {v1,v2,...}, {v1,v2,...}, ... };

Examples​

int arr[][] = { { 10, 20 }, { 30, 40 }, { 50, 60 } };

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

Lab276.java​

class Lab276 {

  public static void main(String[] args) {
    int arr[][] = null;

    arr = new int[3][2];

    System.out.println("Len :" + arr.length);
    System.out.println("Len :" + arr[0].length);
    System.out.println("Len :" + arr[1].length);
    System.out.println("Len :" + arr[2].length);
  }
}

Lab277.java​

class Lab277 {

  public static void main(String[] args) {
    int arr[][] = null;

    arr = new int[3][2];

    arr[0][0] = 10;
    arr[0][1] = 20;
    arr[1][0] = 30;
    arr[1][1] = 40;
    arr[2][0] = 50;
    arr[2][1] = 60;

    System.out.println("Using Normal For loop");

    for (int i = 0; i < arr.length; i++) {
      for (int j = 0; j < arr[i].length; j++) {
        System.out.print("\t" + arr[i][j]);
      }
      System.out.println();
    }

    System.out.println("\nUsing Enhanced for loop");

    for (int a[] : arr) {
      for (int a1 : a) {
        System.out.print("\t" + a1);
      }
      System.out.println();
    }
  }
}

💡 Quick Understanding​

  • arr.length → number of rows
  • arr[i].length → number of columns in each row
  • 2D arrays can be irregular (jagged) ✔
  • You can use:
    • Normal for loop
    • Enhanced for-each loop

Lab278.java​

class Lab278 {

  public static void main(String[] args) {
    int arr[][] = null;
    arr = new int[][]; //  invalid (size must be specified)
    System.out.println("L : " + arr.length);
  }
}

Lab279.java​

class Lab279 {

  public static void main(String[] args) {
    int arr[][] = null;
    arr = new int[][3]; //  invalid (first dimension required)
    System.out.println("Len : " + arr.length);
  }
}

Lab280.java​

class Lab280 {

  public static void main(String[] args) {
    int arr[][] = null;
    arr = new int[3][]; // ✔ valid

    System.out.println("Len : " + arr.length);

    for (int i = 0; i < arr.length; i++) System.out.println(arr[i]);
  }
}

Lab281.java​

class Lab281 {

  public static void main(String[] args) {
    int arr[][] = null;
    arr = new int[3][2];

    System.out.println("Len : " + arr.length);

    arr[0] = 1234; //  invalid (expects int[])
    System.out.println(arr[0]);
  }
}

Lab282.java​

class Lab282 {

  public static void main(String[] args) {
    int arr[][] = null;
    arr = new int[3][2];

    arr[0][0] = 1234;
    System.out.println(arr[0][0]);
  }
}

Lab283.java​

class Lab283 {

  public static void main(String[] args) {
    int arr[][] = null;
    arr = new int[3][];

    int tmp[] = { 99, 88, 77, 66, 55 };

    System.out.println("L : " + arr.length);

    arr[0] = new int[4]; // ✔ valid
    arr[1] = new int[] { 10, 30, 20 }; // ✔ valid
    arr[2] = tmp; // ✔ valid

    for (int ar[] : arr) {
      for (int a : ar) System.out.print("\t" + a);
      System.out.println();
    }
  }
}

Lab284.java​

class Lab284 {

  public static void main(String[] args) {
    int arr[][] = {
      { 10, 23, 21 },
      { 12 },
      { 23, 43, 12, 32 },
      { 98, 34, 32 },
    };

    for (int ar[] : arr) {
      for (int a : ar) System.out.print("\t" + a);
      System.out.println();
    }
  }
}

Lab285.java​

class Lab285 {

  public static void main(String[] args) {
    int arr[][] = null;

    arr = new int[][] {
      { 10, 23, 21 },
      { 12 },
      { 23, 43, 12, 32 },
      { 98, 34, 32 },
    };

    for (int ar[] : arr) {
      for (int a : ar) System.out.print("\t" + a);
      System.out.println();
    }
  }
}

💡 Quick Understanding​

  • new int[][] → size required
  • new int[][3] → first dimension mandatory
  • new int[3][] ✔ → allowed (jagged array)
  • arr[0] → must be int[], not int
  • 2D arrays in Java are jagged (rows can have different sizes) ✔