Array-Basics in Java Multidimensional Arrays can be defined in simple words as array of arrays. Data in multidimensional arrays are stored in tabular form (in row major order).
Syntax:
data_type[1st dimension][2nd dimension][]..[Nth dimension] array_name = new data_type[size1][size2]….[sizeN];
where:
- data_type: Type of data to be stored in the array. For example: int, char, etc.
- dimension: The dimension of the array created. For example: 1D, 2D, etc.
- array_name: Name of the array
- size1, size2, …, sizeN: Sizes of the dimensions respectively.
Examples:
Two dimensional array:
int[][] twoD_arr = new int[10][20];
Three dimensional array:
int[][][] threeD_arr = new int[10][20][30];
Size of multidimensional arrays: The total number of elements that can be stored in a multidimensional array can be calculated by multiplying the size of all the dimensions.
For example: The array int[][] x = new int[10][20] can store a total of (10*20) = 200 elements. Similarly, array int[][][] x = new int[5][10][20] can store a total of (5*10*20) = 1000 elements.
Application of Multi-Dimensional Array
● Multidimensional arrays are used to store the data in a tabular form. For example, storing the roll number and marks of a student can be easily done using multidimensional arrays. Another common usage is to store the images in 3D arrays.
● In dynamic programming questions, multidimensional arrays are used which are used to represent the states of the problem.
● Apart from these, they also have applications in many standard algorithmic problems like: Matrix Multiplication, Adjacency matrix representation in graphs, Grid search problems
Two – dimensional Array (2D-Array)
Two – dimensional array is the simplest form of a multidimensional array. A two – dimensional array can be seen as an array of one – dimensional array for easier understanding.
Indirect Method of Declaration:
- Declaration – Syntax:
data_type[][] array_name = new data_type[x][y];
For example: int[][] arr = new int[10][20];
- Initialization – Syntax:
array_name[row_index][column_index] = value;
For example: arr[0][0] = 1;
Example: 1
import java.io.*;
public class GFG {
public static void main(String[] args)
{
int[][] arr = new int[10][20];
arr[0][0] = 1;
System.out.println("arr[0][0] = " + arr[0][0]);
}
} |
arr[0][0] = 1
Example: Implementing 2D array with by default values with 4*4 matrix
public class TwoDArray {
public static void main(String[] args) {
int rows = 4;
int columns = 4;
int[][] array = new int[rows][columns];
int value = 1;
for (int i = 0; i < rows; i++) {
for (int j = 0; j < columns; j++) {
array[i][j] = value;
value++;
}
}
System.out.println("The 2D array is: ");
for (int i = 0; i < rows; i++) {
for (int j = 0; j < columns; j++) {
System.out.print(array[i][j] + " ");
}
System.out.println();
}
}
} |
The 2D array is: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Explanation:
-
The number of rows and columns are specified using the variables rows and columns. The 2D array is created using the new operator, which allocates memory for the array. The size of the array is specified by rows and columns.
Direct Method of Declaration: Syntax:
data_type[][] array_name = {
{valueR1C1, valueR1C2, ....},
{valueR2C1, valueR2C2, ....}
};
For example: int[][] arr = {{1, 2}, {3, 4}};
Example:
import java.io.*;
class GFG {
public static void main(String[] args)
{
int[][] arr = { { 1, 2 }, { 3, 4 } };
for (int i = 0; i < 2; i++)
for (int j = 0; j < 2; j++)
System.out.println("arr[" + i + "][" + j + "] = "
+ arr[i][j]);
}
} |
arr[0][0] = 1 arr[0][1] = 2 arr[1][0] = 3 arr[1][1] = 4
Accessing Elements of Two-Dimensional Arrays
Elements in two-dimensional arrays are commonly referred by x[i][j] where ‘i’ is the row number and ‘j’ is the column number.
Syntax:
x[row_index][column_index]
For example:
int[][] arr = new int[10][20];
arr[0][0] = 1;
The above example represents the element present in first row and first column. Note: In arrays if size of array is N. Its index will be from 0 to N-1. Therefore, for row_index 2, actual row number is 2+1 = 3. Example:
import java.io.*;
class GFG {
public static void main(String[] args)
{
int[][] arr = { { 1, 2 }, { 3, 4 } };
System.out.println("arr[0][0] = " + arr[0][0]);
}
} |
arr[0][0] = 1
Representation of 2D array in Tabular Format:
A two – dimensional array can be seen as a table with ‘x’ rows and ‘y’ columns where the row number ranges from 0 to (x-1) and column number ranges from 0 to (y-1). A two – dimensional array ‘x’ with 3 rows and 3 columns is shown below:
Print 2D array in tabular format:
To output all the elements of a Two-Dimensional array, use nested for loops. For this two for loops are required, One to traverse the rows and another to traverse columns.
Example:
import java.io.*;
class GFG {
public static void main(String[] args)
{
int[][] arr = { { 1, 2 }, { 3, 4 } };
for (int i = 0; i < 2; i++) {
for (int j = 0; j < 2; j++) {
System.out.print(arr[i][j] + " ");
}
System.out.println();
}
}
} |
1 2 3 4
Example: Implementation of 2D array with User input
import java.util.Scanner;
public class Main {
public static void main(String[] args)
{
Scanner scan = new Scanner(System.in);
System.out.print("Enter number of rows: ");
int rows = scan.nextInt();
System.out.print("Enter number of columns: ");
int columns = scan.nextInt();
int[][] multidimensionalArray= new int[rows][columns];
// Now you can use the array like a regular
// 2-dimensional array
for (int i = 0; i < rows; i++) {
for (int j = 0; j < columns; j++) {
multidimensionalArray[i][j]= (i + 1) * (j + 1);
}
}
for (int i = 0; i < rows; i++) {
for (int j = 0; j < columns; j++) {
System.out.print(multidimensionalArray[i][j]+ " ");
}
System.out.println();
}
scan.close();
}
} |
Output
Enter number of rows: 3
Enter number of columns: 3
1 2 3
2 4 6
3 6 9
- This code prompts the user to enter the number of rows and columns for the 2-dimensional array. The Scanner class is used to read the user input. Then it creates a 2-dimensional array of integers with the specified number of rows and columns, and assigns each element of the array with i*j.
- If you want to create a multidimensional array with more than two dimensions, you can use the same approach of creating an array of arrays. For example, to create a 3-dimensional array, you can create an array of 2-dimensional arrays.
Three – dimensional Array (3D-Array)
Three – dimensional array is a complex form of a multidimensional array. A three-dimensional array can be seen as an array of two – dimensional array for easier understanding.
Indirect Method of Declaration:
- Declaration – Syntax:
data_type[][][] array_name = new data_type[x][y][z];
For example: int[][][] arr = new int[10][20][30];
- Initialization – Syntax:
array_name[array_index][row_index][column_index] = value;
For example: arr[0][0][0] = 1;
Example:
import java.io.*;
class GFG {
public static void main(String[] args)
{
int[][][] arr = new int[10][20][30];
arr[0][0][0] = 1;
System.out.println("arr[0][0][0] = " + arr[0][0][0]);
}
} |
arr[0][0][0] = 1
Direct Method of Declaration: Syntax:
data_type[][][] array_name = {
{
{valueA1R1C1, valueA1R1C2, ....},
{valueA1R2C1, valueA1R2C2, ....}
},
{
{valueA2R1C1, valueA2R1C2, ....},
{valueA2R2C1, valueA2R2C2, ....}
}
};
For example: int[][][] arr = { {{1, 2}, {3, 4}}, {{5, 6}, {7, 8}} };
Example:
import java.io.*;
class GFG {
public static void main(String[] args)
{
int[][][] arr = { { { 1, 2 }, { 3, 4 } }, { { 5, 6 }, { 7, 8 } } };
for (int i = 0; i < 2; i++)
for (int j = 0; j < 2; j++)
for (int z = 0; z < 2; z++)
System.out.println("arr[" + i
+ "]["
+ j + "]["
+ z + "] = "
+ arr[i][j][z]);
}
} |
arr[0][0][0] = 1 arr[0][0][1] = 2 arr[0][1][0] = 3 arr[0][1][1] = 4 arr[1][0][0] = 5 arr[1][0][1] = 6 arr[1][1][0] = 7 arr[1][1][1] = 8
Accessing Elements of Three-Dimensional Arrays
Elements in three-dimensional arrays are commonly referred by x[i][j][k] where ‘i’ is the array number, ‘j’ is the row number and ‘k’ is the column number.
Syntax:
x[array_index][row_index][column_index]
For example:
int[][][] arr = new int[10][20][30];
arr[0][0][0] = 1;
The above example represents the element present in the first row and first column of the first array in the declared 3D array.
Note: In arrays if size of array is N. Its index will be from 0 to N-1. Therefore, for row_index 2, actual row number is 2+1 = 3.
Example:
import java.io.*;
class GFG {
public static void main(String[] args)
{
int[][][] arr = { { { 1, 2 }, { 3, 4 } }, { { 5, 6 }, { 7, 8 } } };
System.out.println("arr[0][0][0] = " + arr[0][0][0]);
}
} |
arr[0][0][0] = 1
Representation of 3D array in Tabular Format:
A three-dimensional array can be seen as a table of arrays with ‘x’ rows and ‘y’ columns where the row number ranges from 0 to (x-1) and column number ranges from 0 to (y-1). A three – dimensional array with 3 array containing 3 rows and 3 columns is shown below:
Print 3D array in tabular format:
To output all the elements of a Three-Dimensional array, use nested for loops. For this three for loops are required, One to traverse the arrays, second to traverse the rows and another to traverse columns.
Example:
import java.io.*;
class GFG {
public static void main(String[] args)
{
int[][][] arr = { { { 1, 2 }, { 3, 4 } },
{ { 5, 6 }, { 7, 8 } } };
for (int i = 0; i < 2; i++) {
for (int j = 0; j < 2; j++) {
for (int k = 0; k < 2; k++) {
System.out.print(arr[i][j][k] + " ");
}
System.out.println();
}
System.out.println();
}
}
} |
1 2 3 4 5 6 7 8
Inserting a Multi-dimensional Array during Runtime:
This topic is forced n taking user-defined input into a multidimensional array during runtime. It is focused on the user first giving all the input to the program during runtime and after all entered input, the program will give output with respect to each input accordingly. It is useful when the user wishes to make input for multiple Test-Cases with multiple different values first and after all those things are done, program will start providing output. As an example, let’s find the total number of even and odd numbers in an input array. Here, we will use the concept of a 2-dimensional array.
Here are a few points that explain the use of the various elements in the upcoming code:
- Row integer number is considered as the number of Test-Cases and Column values are considered as values in each Test-Case.
- One for() loop is used for updating Test-Case number and another for() loop is used for taking respective array values.
- As all input entry is done, again two for() loops are used in the same manner to execute the program according to the condition specified.
- The first line of input is the total number of TestCases.
- The second line shows the total number of first array values.
- The third line gives array values and so on.
Implementation:
import java.io.*;
import java.util.Scanner;
class GFGTestCase {
public static void main(String[] args)
{
// Scanner class to take
// values from console
Scanner scanner = new Scanner(System.in);
// totalTestCases = total
// number of TestCases
// eachTestCaseValues =
// values in each TestCase as
// an Array values
int totalTestCases, eachTestCaseValues;
// takes total number of
// TestCases as integer number
totalTestCases = scanner.nextInt();
// An array is formed as row
// values for total testCases
int[][] arrayMain = new int[totalTestCases][];
// for loop to take input of
// values in each TestCase
for (int i = 0; i < arrayMain.length; i++) {
eachTestCaseValues = scanner.nextInt();
arrayMain[i] = new int[eachTestCaseValues];
for (int j = 0; j < arrayMain[i].length; j++) {
arrayMain[i][j] = scanner.nextInt();
}
} // All input entry is done.
// Start executing output
// according to condition provided
for (int i = 0; i < arrayMain.length; i++) {
// Initialize total number of
// even & odd numbers to zero
int nEvenNumbers = 0, nOddNumbers = 0;
// prints TestCase number with
// total number of its arguments
System.out.println("TestCase " + i + " with "
+ arrayMain[i].length
+ " values:");
for (int j = 0; j < arrayMain[i].length; j++) {
System.out.print(arrayMain[i][j] + " ");
// even & odd counter updated as
// eligible number is found
if (arrayMain[i][j] % 2 == 0) {
nEvenNumbers++;
}
else {
nOddNumbers++;
}
}
System.out.println();
// Prints total numbers of
// even & odd
System.out.println(
"Total Even numbers: " + nEvenNumbers
+ ", Total Odd numbers: " + nOddNumbers);
}
}
}// This code is contributed by Udayan Kamble. |
Output:
Input:
2
2
1 2
3
1 2 3
Output:
TestCase 0 with 2 values:
1 2
Total Even numbers: 1, Total Odd numbers: 1
TestCase 1 with 3 values:
1 2 3
Total Even numbers: 1, Total Odd numbers: 2
Input:
3
8
1 2 3 4 5 11 55 66
5
100 101 55 35 108
6
3 80 11 2 1 5
Output:
TestCase 0 with 8 values:
1 2 3 4 5 11 55 66
Total Even numbers: 3, Total Odd numbers: 5
TestCase 1 with 5 values:
100 101 55 35 108
Total Even numbers: 2, Total Odd numbers: 3
TestCase 2 with 6 values:
3 80 11 2 1 5
Total Even numbers: 2, Total Odd numbers: 4