2D Arrays

Array of arrays
Can be initialized using [][] (double brackets)
Two for loops can be used to traverse through each row and then each column in the 2d array
Specify index by row and column to access 2d array (like a matrix
Change how you print and display them according to row/column and iterate through them in different ways to go through them

2D Array HW

import java.util.Scanner;

public class Arrays{
    int[][] numbers;
    public Arrays(){
        int[][] newArray = new int[4][4];;
        for (int i = 0; i < newArray.length; i++){
            for (int j = 0; j < newArray[i].length; j++){
                newArray[i][j] = (j+1) * (int) (Math.random()*10);
            }
        }

        this.numbers = newArray;
    }

    public void printArray(){
        for(int i = 0; i < numbers.length; i++){
            for(int j = 0; j < numbers[i].length; j++){
                System.out.print(numbers[i][j] + " ");
            }

            System.out.println();

        }
    }

    public void reverseArray(){
        System.out.println("\n\nPrinting out values backward");
        for(int i = numbers.length-1;i>=0;i--){
            for(int j = numbers[i].length-1; j >= 0;j--){ 
                System.out.print(numbers[i][j] + " ");
            }
            System.out.println(" ");
        }
    }

    public void askForIndex(){
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter Row Index: ");
        int rowIndex = scanner.nextInt();
        System.out.println(rowIndex);

        System.out.print("Enter Column Index: ");
        int columnIndex = scanner.nextInt();
        System.out.println(columnIndex);

        System.out.print("Result: "); 
        System.out.println(numbers[rowIndex][columnIndex]);
    }

    public void multiplyThenSum(){
        int sum = 0;

        for(int i = 0; i < numbers.length; i++){
            int multiply = 1;

            for(int j = 0; j < numbers[i].length; j++){
                multiply *= numbers[i][j];
            }

            sum += multiply;
        }

        System.out.print("Sum: ");
        System.out.println(sum);
    }

    public static void main(String[] args){
        Arrays array = new Arrays();
        array.printArray();
        array.reverseArray();
        array.askForIndex();
        array.multiplyThenSum();

    }
}

Arrays.main(null);

7 10 21 0 
9 16 0 8 
6 10 18 36 
2 6 12 16 


Printing out values backward
16 12 6 2  
36 18 10 6  
8 0 16 9  
0 21 10 7  
Enter Row Index: 0
Enter Column Index: 0
Result: 7
Sum: 41184