Add more element to a 3×3 2D array

I’m writing an inventory list program, that provides the user with option of adding an item to the list of exiting the program. To add an item the user enters 1 and is promoted to enter the item details( item name, price and quantity of the items). The information enter by the user is entered into a 3×3 2D array table, which already has a few values in it. The problem here is that I am finding it difficult to update/add new elements to the 3×3 2D array table. I’ve searched the internet for solutions, but I couldn’t find any. Below is a code snippet of the 3×3 2D array table I wrote.

import java.util.Arrays;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // put your code here
        int[][] one_d_array = {{2, 4, 6, 8}, {3, 5, 7, 9}};
        int newArr[][] = new int[one_d_array.length + 1][one_d_array.length + 1];
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter your desired number:");
        int num = sc.nextInt();
        System.out.println("Enter your desired number:");
        int num2 = sc.nextInt();
        //System.out.println(Arrays.toString(oned_array));
        for (int i = 0; i < one_d_array.length; i++) {
            for (int j = 0; j < one_d_array.length; j++) {
                newArr[i][j] = one_d_array[i][j];
            }
        }
        newArr[one_d_array.length][one_d_array.length] = ;
        System.out.println(Arrays.toString(newArr));
    }
}

P.S I’m new to arrays and don’t really know how to use them.

Answer

Here is a break-down of one way this can be done. Read the comments in code:

// A 2x4 int[] array (2 Rows by 4 Columns in Each Row):
int[][] one_d_array = { // C0 C1 C2 C3      C = Column
                         { 2, 4, 6, 8 },    // Row 0
                         { 3, 5, 7, 9 }     // Row 1  
                      };
    
// Display the current Array into the Console window:
System.out.println("Your Current 2D Array (one_d_array):");
for (int[] ary : one_d_array) {
    System.out.println(Arrays.toString(ary));
}
System.out.println();
    
/* Adding an additional Column to each Row:
   One way to do this is to recreate the original 
   Array with the help of a temporary array:   */
/* If you don't want to change the number of Rows
   then remove the `+ 1` from newNumberOfRows:  */
int newNumberOfRows    = one_d_array.length;      // one_d_array.length + 1;
int newNumberOfColumns = one_d_array[0].length + 1;
    
/* Declare and initialize a new 2D Array to accommodate 
   your desired new size (in this case columns +1).   */
int[][] newArr = new int[newNumberOfRows][newNumberOfColumns];
    
/* Copy the Original Array (one_d_array) into the new Array (newArr). 
   We'll use the `System.arraycopy()` method to do this. This will fill
   your new 2D array with the data from the Original 2D Array except 
   for the new Column(s) you added.                             */
for (int i = 0; i < one_d_array.length; i++) {
    System.arraycopy(one_d_array[i], 0, newArr[i], 0, one_d_array[i].length);
}
    
Scanner sc = new Scanner(System.in); // Open a Stream for keyboard input.
   
// User to supply Data values to the new columns in each row:
int num;
for (int i = 0; i < newNumberOfRows; i++) {
    System.out.print("Enter your desired number for Column #" 
                 + newNumberOfColumns + " of Row #" + (i+1) + ": -> ");
    num = sc.nextInt();
    /* We subtract 1 from newNumberOfColumns because array 
       indexes start from 0. newNumberOfColumns holds a literal
       value.                             */
    newArr[i][newNumberOfColumns - 1] = num; 
}
    
// Copy the new Array (newArr) into the Original Array (one_d_array)
one_d_array = new int[newArr.length][newArr[0].length];
for (int i = 0; i < newArr.length; i++) {
    System.arraycopy(newArr[i], 0, one_d_array[i], 0, newArr[i].length);
}
    
// Print the Modified Original Array to the Console Window:
System.out.println();
System.out.println("Your Modified 2D Array (one_d_array):");
for (int[] ary : one_d_array) {
    System.out.println(Arrays.toString(ary));
}

When run, your console output should look something like this:

Your Current 2D Array (one_d_array):
[2, 4, 6, 8]
[3, 5, 7, 9]

Enter your desired number for Column #5 of Row #1: -> 24
Enter your desired number for Column #5 of Row #2: -> 36

Your Modified 2D Array (one_d_array):
[2, 4, 6, 8, 24]
[3, 5, 7, 9, 36]

Consider using a List or an ArrayList as these can grow and shrink dynamically.