How to do matrices in java

Creating a matrix in java

Question: I’m trying to make a program that will make square matrices based on user input. Either read the numbers in from a file and output them to the screen, or have the user type them as user input and output the matrix to a file.

Creating a matrix in java

I want to create a matrix in java .. I implemented the following code

public class Tester < public static void main(String[] args) < int[][] a = new int[2][0]; a[0][0] = 3; a[1][0] = 5; a[2][0] = 6; int max = 1; for (int x = 0; x < a.length; x++) < for (int b = 0; b < a[x].length; b++) < if (a[x][b] >max) < max = a[x][b]; System.out.println(max); >System.out.println(a[x][b]); > > System.out.println(a[x][b]); > > 

When I run the code I get the following error :

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0 at shapes.Tester.main(Tester.java:8) 

I tried different methods to correct the code but nothing was helpful Can you please correct the code for me ?

When you instantiate an array, you’re giving it sizes, not indices. So to use the 0th index, you need at least a size of 1.

This will instantiate a 3×1 «matrix», meaning that valid indices for the first set of brackets are 0, 1 and 2; while the only valid index for the second set of brackets is 0. This looks like what your code requires.

public static void main(String[] args) < // When instantiating an array, you give it sizes, not indices int[][] arr = new int[3][1]; // These are all the valid index combinations for this array arr[0][0] = 3; arr[1][0] = 5; arr[2][0] = 6; int max = 1; // To use these variables outside of the loop, you need to // declare them outside the loop. int x = 0; int y = 0; for (; x < arr.length; x++) < for (; y < arr[x].length; y++) < if (arr[x][y] >max) < max = arr[x][y]; System.out.println(max); >System.out.println(arr[x][y]); > > // This print statement accesses x and y outside the loop System.out.println(arr[x][y]); > 

Your storing 3 elements in the first array.

try this int[][] a = new int[3][1];

Creating a 2d matrix from an array (java), Assign array [i] to matrix [row] [col]. For bonus points, note that the last row is often shorter than the other rows. Allocating matrix = new int [] [a] …

How can I create a matrix with Java and add all its elements to a sum?

I need to write a code in Java which creates a 3000X3000 matrix, where each element is a integer type. After this I need to add all the elements.

I was given this part of code:

But since I never worked with arrays before, actually we just talked about arrays today the first time. I don’t really get how I need to customize this code, so that I end up with the sum of all the elements inside this matrix.

You can use two loops and iterate over array and store integer value in them.

public static void main(String[] args) < long sum = 0; int dimension = 3000; int i, j; int matrix[][] = new int[dimension][dimension]; for (i = 0; i < dimension; i++) < for (j = 0; j < dimension; j++) < matrix[i][j] = 1; // Number you want to store, could be a scanner input >> for (i = 0; i < dimension; i++) < for (j = 0; j < dimension; j++) < sum = sum + matrix[i][j]; >> System.out.println(sum); > 

An array is simply a list of something. A matrix, in Java, would be a list of lists, so to access one point in the grid, you access arr[y][x] , where x is the x position, and y is the y position.

So then, to add all of it together, you can use code with this structure:

int sum = 0; // Define the sum to add to int[][] grid = new int[] < // Define the grid , , , , >; for (int x = 0; x < grid[0].length; x++) // Loop through X indicies for (int y = 0; y < grid.length; y++) // Loop through Y indicies sum += grid[y][x]; // Add value to the sum 

This code loops through every integer, and adds it to the sum. Remember, the first index is the row, so therefore y , and the second is the column, so therefore x . You loop through both indicies, catching every number stored in the grid and storing it.

I have modified iNan's answer a bit:

public static void main(String[] args) < long sum = 0; int dimension = 3000; int i, j; int matrix[][] = new int[dimension][dimension for (i = 0; i < dimension; i++) < for (j = 0; j < dimension; j++) < matrix[i][j] = 1; // Number you want to store, could be a scanner input sum = sum + matrix[i][j]; >> System.out.println(sum); > 

You don't need to iterate separately over the matrix filling the entries and then iterating over it again summing all the things up. You can fill and sum up in one step accelerating your program a bit. With large matrices it could speed up the program significantly.

Matrix - Add Matrices in Java, Teams. Q&A for work. Connect and share knowledge within a single location that is structured and easy to search. Learn more

How to make a matrix from scratch in java

I'm trying to make a program that will make square matrices based on user input. I know that arrays exist, but I wanted to make a matrix from scratch so that I could better understand the basic concept of it and further extend my understanding of loops. So far I have been able to make a square matrix that will accept one number as an input into that matrix, for example I input a square 2x2 matrix and while I want it to look like this 1 2 3 4 with 1 and 2 being above 3 and 4. I have only gotten it to accept one user input that it places in all four slots. For example, if my user input is 1 then the matrix looks like this 1 1 1 1

My code looks like this thus far:

 int number; System.out.println("What are the dimensions of the matrix?"); number = in.nextInt(); for (int k = 0; k < number; k = k +1) < System.out.println("What are the numbers in your matrix?"); int matrix_number = in.nextInt(); for (int i = 0; i < number; i = i + 1) < for (int j = 0; j < number; j = j + 1) < System.out.print(matrix_number); >System.out.println(); > > 

I believe that my problem lies in my first for loop where I have the user input the matrix number. Any helpful suggestions on how I can better write this so that the user can input a different number for each slot in the matrix?

It looks like you are trying to create a matrix and then populate it with values read from the user.

To create an N x N matrix of integers

Obviously, if you want to read a different value for each cell, you need to call nextInt() multiple times; i.e. once for each value you want to read.

(Note to other readers: I'm not coding this for the OP, because he will learn more by coding it himself.)

You can create a matrix using 2 dimensional arrays:

int[][] matrix = new int[row][column]; //row is the number of matrix rows //column is the number of matrix columns 

To access the elements of the matrix and define it after the declaration, you can use a nested for loop:

As you mention in your question, user has to input only onces and that it places in all four slots. For example, if user input is 1 then the matrix looks like this 1 1 1 1. Then no need for first for loop, just remove it.

 int number; System.out.println("What are the dimensions of the matrix?"); number = in.nextInt(); System.out.println("What are the numbers in your matrix?"); int matrix_number = in.nextInt(); for (int i = 0; i < number; i = i + 1) < for (int j = 0; j < number; j = j + 1) < System.out.print(matrix_number); >System.out.println(); > 

You want the user to say the size of the square matrix, then you want the user to tell you every number in the matrix. You only need two loops here:

int number; System.out.println("What are the dimensions of the matrix?"); number = in.nextInt(); for (int i = 0; i < number; i = i + 1) < for (int j = 0; j < number; j = j + 1) < System.out.println("What are the numbers in your matrix?"); int matrix_number = in.nextInt(); System.out.print(matrix_number); >System.out.println(); > 

If you don't want your matrix polluted by "What are the numbers in your matrix?" questions, then you're going to need to learn how to store user input into some sort of data structure. As you said in your question, arrays are a great way to do this (as are 2d arrays).

If you were willing to learn file input or file output, then you could do what you seek without "storing" the numbers in an array. Either read the numbers in from a file and output them to the screen, or have the user type them as user input and output the matrix to a file.

Edit: You could try to erase the "What are the numbers in your matrix?" system out by printing backspace characters on linux systems. More here: How to delete stuff printed to console by System.out.println()?

Java - Creating a Matrix with ArrayLists, Java works with references. So in your program, mainList will contain 5 references to the same unique intList.Anything you do to intList will reflect in all the "rows" in …

Java : create a matrix of strings

I begin with java and I'm searching for how to create an array 2d of strings : my array 2d should contains :

10 20 "OK" 5 30 "KO" 20 100 "NA" 10 60 "OK" String[][] matrix = new String[i][j]; for(r=0;i

What Florin said, but with simplified for-loop:

String [][] matrix = < , , , >; for (String [] line : matrix) < for (String s: line) < System.out.print ("10 " + s); >> 

All seems good. Maybe you could do a better use of for each loops in java :

String[][] matrix = new String[i][j]; for( String[] rows : matrix)

Arrays - How can I create a matrix with Java and add all, An array is simply a list of something. A matrix, in Java, would be a list of lists, so to access one point in the grid, you access arr[y][x], where x is the x position, and y …

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Matrix Programs in Java

While we believe that this content benefits our community, we have not yet thoroughly reviewed it. If you have any suggestions for improvements, please let us know by clicking the “report an issue“ button at the bottom of the tutorial.

A Matrix is a rectangular array. The elements are arranged in the rows and columns. In this tutorial, we will look at some matrix programs in Java.

Graphical Representation of Matrix

Matrix in Java

We can implement a matrix using two dimensional array in Java. The element at row “r” and column “c” can be accessed using index “array[r][c]”.

Matrix Programs in Java

Since we are using two-dimensional arrays to create a matrix, we can easily perform various operations on its elements. In this tutorial, we will learn how to create a matrix from user input. Then we will add, subtract, and multiply two matrices and print the result matrix on the console.

1. Adding Two Matrix

Here is the simple program to populate two matrices from the user input. Then add its elements at the corresponding indices to get the addition of the matrices. Finally, we will print the sum of the matrices.

package com.journaldev.examples; import java.util.Scanner; public class MatrixPrograms < public static void main(String[] args) < System.out.println("Please enter the rows in the matrix"); Scanner sc = new Scanner(System.in); int row = sc.nextInt(); System.out.println("Please enter the columns in the matrix"); int column = sc.nextInt(); int[][] first = new int[row][column]; int[][] second = new int[row][column]; for (int r = 0; r < row; r++) < for (int c = 0; c < column; c++) < System.out.println(String.format("Enter first[%d][%d] integer", r, c)); first[r][c] = sc.nextInt(); >> for (int r = 0; r < row; r++) < for (int c = 0; c < column; c++) < System.out.println(String.format("Enter second[%d][%d] integer", r, c)); second[r][c] = sc.nextInt(); >> // close the scanner sc.close(); // print both matrices System.out.println("First Matrix:\n"); print2dArray(first); System.out.println("Second Matrix:\n"); print2dArray(second); // sum of matrices sum(first, second); > // below code doesn't take care of exceptions private static void sum(int[][] first, int[][] second) < int row = first.length; int column = first[0].length; int[][] sum = new int[row][column]; for (int r = 0; r < row; r++) < for (int c = 0; c < column; c++) < sum[r][c] = first[r][c] + second[r][c]; >> System.out.println("\nSum of Matrices:\n"); print2dArray(sum); > private static void print2dArray(int[][] matrix) < for (int r = 0; r < matrix.length; r++) < for (int c = 0; c < matrix[0].length; c++) < System.out.print(matrix[r][c] + "\t"); >System.out.println(); > > > 

2. Subtracting Two Matrices

Here is the function to subtraction second matrix elements from the first matrix and then print the result matrix.

private static void subtract(int[][] first, int[][] second) < int row = first.length; int column = first[0].length; int[][] sum = new int[row][column]; for (int r = 0; r < row; r++) < for (int c = 0; c < column; c++) < sum[r][c] = first[r][c] - second[r][c]; >> System.out.println("\nSubtraction of Matrices:\n"); print2dArray(sum); > 

3. Multiplying Two Matrices

private static void multiply(int[][] first, int[][] second) < int row = first.length; int column = first[0].length; int[][] sum = new int[row][column]; for (int r = 0; r < row; r++) < for (int c = 0; c < column; c++) < sum[r][c] = first[r][c] * second[r][c]; >> System.out.println("\nMultiplication of Matrices:\n"); print2dArray(sum); > 

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