Different Ways To Declare And Initialize 2-D Array in Java
Last Updated :
13 Nov, 2024
An array with more than one dimension is known as a multi-dimensional array. The most commonly used multi-dimensional arrays are 2-D and 3-D arrays. We can say that any higher dimensional array is an array of arrays.
A very common example of a 2D Array is Chess Board. A chessboard is a grid containing 64 1x1 square boxes. You can similarly visualize a 2D array. In a 2D array, every element is associated with a row number and column number. Accessing any element of the 2D array is similar to accessing the record of an Excel File using both row number and column number. 2D arrays are useful while implementing a Tic-Tac-Toe game, Chess, or even storing the image pixels.
Example:
Java
import java.io.*;
class GFG {
public static void main(String[] args){
int n = 80, m = 5;
int[][] arr = new int[n][m];
// initializing the array elements using for loop
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
arr[i][j] = i + j;
}
}
// printing the first three rows of marks array
for (int i = 0; i < 3; i++) {
for (int j = 0; j < m; j++)
System.out.printf(arr[i][j] + " ");
System.out.println();
}
}
}
Output0 1 2 3 4
1 2 3 4 5
2 3 4 5 6
Note: We can use arr. length function to find the size of the rows (1st dimension), and arr[0].length function to find the size of the columns (2nd dimension).
Declaring 2-D array in Java
Any 2-dimensional array can be declared as follows:
Syntax:
// Method 1
data_type array_name[][];
// Method 2
data_type[][] array_name;
data_type: Since Java is a statically-typed language (i.e. it expects its variables to be declared before they can be assigned values). So, specifying the datatype decides the type of elements it will accept. e.g. to store integer values only, the data type will be declared as int.
array_name: It is the name that is given to the 2-D array. e.g. subjects, students, fruits, department, etc.
Note: We can write [ ][ ] after data_type or we can write [ ][ ] after array_name while declaring the 2D array.
Initialize 2-D array in Java
data_type[][] array_Name = new data_type[row][col];
The total elements in any 2D array will be equal to (row) * (col).
- row: The number of rows in an array
- col: The number of columns in an array.
When you initialize a 2D array, you must always specify the first dimension(no. of rows), but providing the second dimension(no. of columns) may be omitted. Java compiler is smart enough to manipulate the size by checking the number of elements inside the columns.
// Incorrect Statement
int[][] arr = new int[][3];
// Correct Statement
int[][] arr = new int[2][];
You can access any element of a 2D array using row numbers and column numbers.
Different Ways to Declare and Initialize 2-D Array in Java
1. Inserting Elements while Initialization
In the code snippet below, we have not specified the number of rows and columns. However, the Java compiler is smart enough to manipulate the size by checking the number of elements inside the rows and columns.
Java
import java.io.*;
class GFG {
public static void main(String[] args)
{
// Create a String Array
String[][] subjects = {
// Row 1
{ "Data Structures & Algorithms",
"Programming & Logic",
"Software Engineering",
"Theory of Computation" },
// Row 2
{ "Thermodynamics",
"Metallurgy",
"Machine Drawing",
"Fluid Mechanics" },
// Row 3
{ "Signals and Systems",
"Digital Electronics",
"Power Electronics" }
};
// Printing the Array Spoecific Index
System.out.println(subjects[0][0]);
System.out.println(subjects[1][3]);
System.out.println(subjects[2][1]);
}
}
OutputData Structures & Algorithms
Fluid Mechanics
Digital Electronics
2. Inserting Elements by Index
Moreover, we can initialize each element of the array separately. Look at the code snippet below:
Java
import java.io.*;
import java.util.*;
class GFG {
public static void main(String[] args){
// Creating and Initialization of
// Array
int[][] scores = new int[2][2];
// Inserting elements in the specific index
scores[0][0] = 15;
scores[0][1] = 23;
scores[1][0] = 30;
scores[1][1] = 21;
// Printing the array elements individually
System.out.print(scores[0][0]+" ");
System.out.println(scores[0][1]);
System.out.print(scores[1][0]+" ");
System.out.println(scores[1][1]);
}
}
3. Inserting Elements in Jagged Array
There may be a certain scenario where you want every row to have a different number of columns. This type of array is called a Jagged Array.
Java
import java.io.*;
class GFG {
public static void main(String[] args){
// declaring a 2D array with 2 rows
int arr[][] = new int[2][];
// Jagged array with custom
// columns for each row
arr[0] = new int[2];
arr[1] = new int[4];
// Initializing the array
int count = 0;
for (int i = 0; i < arr.length; i++) {
for (int j = 0; j < arr[i].length; j++) {
arr[i][j] = count++;
}
}
// Printing the values of 2D Jagged array
for (int i = 0; i < arr.length; i++) {
for (int j = 0; j < arr[i].length; j++)
System.out.printf(arr[i][j] + " ");
System.out.println();
}
}
}
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