Develop Reference

How do I get rid of java.lang.NumberFormatException error

This code takes two txt files, reads them puts them in 2d arrays and should check if the numbers in the files are magic squares but it keeps returning NumberFormatException error. I'm new to java so if anyone could help me that would be great. I'm pretty sure the problem come from the txt file being string and the 2d array needing to be in int form. But how and where do I make that conversion on my code?
this is what i have:
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Arrays;
import java.util.Scanner;
public class ms {
public static void main(String[] args) throws FileNotFoundException {
String filename1 = "magicSquaresData.txt", filename2 = "magicSquaresData.txt";
int nos[][] = null;
nos = getArray(filename1);
boolean b = isMagicSquare(nos);
printArray(nos);
if (b) {
System.out.println("It is a magic Square");
} else {
System.out.println("It is not a magic Square");
}
System.out.println("\n");
nos = getArray(filename2);
b = isMagicSquare(nos);
printArray(nos);
if (b) {
System.out.println("It is a magic Square");
} else {
System.out.println("It is not a magic Square");
}
}
private static int[][] getArray(String filename) throws FileNotFoundException {
String line;
int nos[][] = null;
int size = 0, rows = 0;
Scanner sc = null;
try {
sc = new Scanner(new File(filename));
while (sc.hasNext()) {
if (!sc.nextLine().isEmpty())
size++;
}
sc.close();
nos = new int[size][size];
sc = new Scanner(new File(filename));
while (sc.hasNext()) {
line = sc.nextLine();
if (!line.isEmpty()) {
String arr[] = line.split("\t");
for (int i = 0; i < arr.length; i++) {
nos[rows][i] = Integer.valueOf(arr[i]);
}
rows++;
}
}
sc.close();
} catch (FileNotFoundException e) {
System.out.println(e);
}
return nos;
}
private static void printArray(int[][] nos){
for(int i = 0; i<nos[0].length;i++) {
for (int j = 0; j < nos[0].length; j++){
System.out.printf("%-3d",nos[i][j]);
}
System.out.println();
}
}
private static boolean isMagicSquare(int[][] square) {
boolean bool = true;
int order = square.length;
int[] sumRow = new int[order];
int[] sumCol = new int[order];
int[] sumDiag = new int[2];
Arrays.fill(sumRow, 0);
Arrays.fill(sumCol, 0);
Arrays.fill(sumDiag, 0);
for (int row = 0; row < order; row++){
for (int col = 0; col < order; col++) {
sumRow[row] += square[row][col];
}
}
for (int col = 0; col < order; col++) {
for (int row = 0; row < order; row++) {
sumCol[col] += square[row][col];
}
}
for (int row = 0; row < order; row++) {
sumDiag[0] += square[row][row];
}
for (int row = 0; row < order; row++) {
sumDiag[1] += square[row][order - 1 - row];
}
bool = true;
int sum = sumRow[0];
for (int i = 1; i < order; i++) {
bool = bool && (sum == sumRow[i]);
}
for (int i = 0; i < order; i++) {
bool = bool && (sum == sumCol[i]);
}
for (int i = 0; i < 2; i++) {
bool = bool && (sum == sumDiag[i]);
}
return bool;
}
}

SUGGESTION:
Substitute nos[rows][i] = Integer.valueOf(arr[i]); for a custom method that will tell you WHERE the error is occurring.
EXAMPLE:
public static Integer tryParse(String text, int row, int i) {
try {
return Integer.parseInt(text);
} catch (NumberFormatException e) {
System.out.println("ERROR: row=" + row + ", i=" + i + ", text=" + text);
return null;
}
}
CAVEAT: This is for helping you troubleshoot ONLY. You definitely wouldn't want to release this in "production code" ;)

What is the NumberFormatException?
Thrown to indicate that the application has attempted to convert a string to one of the numeric types, but that the string does not have the appropriate format.
Offtopic:
A thing that i can notice is that both filesnames have the same name. So you will verify the same file 2 times.
String filename1 = "magicSquaresData.txt", filename2 = "magicSquaresData.txt";
I checked your program and you error appears when you put like this on a file:
1. 5 5
2. 5 5
So the error shows beacause you are trying to parse to int the String "5 5". So your code pick the all line and tries to convert to int and " " it's not an int. And there lives the NumberFormatException error.
How do to solve it?
The function that we will work on is the one that you pass from file to an array in
private static int[][] getArray(String filename) throws FileNotFoundException{
The of the function is after we read the file.
As you said, you are leading with a 2d array so to insert all the numbers we need to have loops for each dimension on the array.
So we will start from there.
I will use a while beacause we are dealing with a string and it's easier to verify the text that its left on the line. Will add a new int variable that starts in 0 to pass in every column of a line to use with the while loop. And with this we got this:
for (int i = 0; i < lines.length; i++) {
while(!"".equals(line)){
whileIterator++;
}
whileIterator = 0;
}
Next setep, we will divide in 2 behaviors because we will substring the String that has in the line, and will work differently when it's the last number that we are verifying:
for (int i = 0; i < lines.length; i++) {
while(!"".equals(line)){
if(whileIterator + 1 == size){//If its the last iteration that we need in a line
}else{//All other iterations
whileIterator++;
}
whileIterator = 0;}
To finalize let's add the new logic to insert in nos array. So lets pick all line for example 2 7 6 and we want to add the number 2, so lets do that. You just need to substring(int startIndex, int finalIndex) the line and add to the nos array. After that let remove the number and the space ("2 ") from the line that we are veryfying.
for (int i = 0; i < lines.length; i++) {
while(!"".equals(line)){
if(whileIterator + 1 == size){//If its the last iteration that we need
nos[rows][whileIterator] = Integer.parseInt(line.substring(0));//Add to array
line = "";//To not pass the while verification
}else{//All other iterations
nos[rows][whileIterator] = Integer.parseInt(line.substring(0, line.indexOf(" ")));//Add to array
line = line.substring(line.indexOf(" ") + 1);//remove the number we added behind
}
whileIterator++;
}
whileIterator = 0;}
And here you go, that how you add the numbers to an array and don't get the error.
If you need some further explanation just ask. Hope it helps :)

Going back and forth with methods in Java

I built a tic tac toe game using java but I just have one issue. I want my code to bounce back and forth from the validPlayerOneInput and validPlayerTwoInput methods. As you can see in my main, I'm calling both methods procedurally which be incorrect as it just stops after the method is called. I want this to keep running until a winner is determined.
How do I do so?
import java.util.*;
public class tictactoe {
private static char board[][] = {{1,2,3}, {4,5,6}, {7,8,9}};
char p1Sym, p2Sym;
public tictactoe() {
p1Sym ='X';
p2Sym = 'O';
boardFill();
}
void boardFill() {
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
System.out.print(board[i][j]);
System.out.print(" | ");
}
System.out.println();
}
}
void validInputPlayerOne() {
boolean isSet = true;
int player1Input, player1CorrectedInput;
System.out.println("Player 1, enter a number between 1-9: ");
Scanner player1 = new Scanner(System.in);
player1Input = player1.nextInt();
Scanner correctedInput = new Scanner(System.in);
while(player1Input < 1 || player1Input >= 10) {
System.out.println("This isn't a number between 1-9, try again: ");
player1CorrectedInput = correctedInput.nextInt();
player1Input = player1CorrectedInput;
}
// or
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
if (board[i][j] == player1Input) {
// set new value
board[i][j] = p1Sym;
// set
isSet = true;
}
}
}
if (!isSet) {
System.out.println("not found");
}
}
void validInputPlayerTwo() {
boolean isSet = true;
int player2Input, player2CorrectedInput;
System.out.println("Player 2, enter a number between 1-9: ");
Scanner player2 = new Scanner(System.in);
player2Input = player2.nextInt();
Scanner correctedInput = new Scanner(System.in);
while(player2Input < 1 || player2Input >= 10) {
System.out.println("This isn't a number between 1-9, try again: ");
player2CorrectedInput = correctedInput.nextInt();
player2Input = player2CorrectedInput;
}
// or
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
if (board[i][j] == player2Input){
board[i][j] = p2Sym;
isSet = true;
}
}
}
if (!isSet) {
System.out.println("not found");
}
}
public static void main(String[] args) {
tictactoe t = new tictactoe();
t.validInputPlayerOne();
t.boardFill();
t.validInputPlayerTwo();
t.boardFill();
}
}

You could do something like:
int turn = 0;
while (t.noWinner()) {
if (turn % 2 == 0) t.validInputPlayerOne();
else t.validInputPlayerTwo();
t.boardFill();
turn += 1;
}
Of course, now you have to actually write the noWinner function.

Answering your question directly, you could have a boolean that toggles on each move:
boolean firstPlayer = true;
while (t.gameIsNotFinished()) {
if (firstPlayer)
t.validInputPlayerOne();
else
t.validInputPlayerTwo();
firstPlayer = !firstPlayer;
}
However you have a lot of other issues with your code that you need to address. For example if a player enters an invalid value then it goes to the next player rather than asking for them to reenter the value.
You should also try to have a single validInputPlayer method that works for both players with the firstPlayer variable passed in. At the moment you have a lot of repeated code in those methods.

Matching array values with variables

In this code I have an array with 5 elements and each element contains a value. Below in the while loop, I'm trying to give the user 3 attempts to guess what number is contained in the array (the user enters their guesses). My problem is that I don't know how to make match the user's guess (stored in a variable choose) with the array values caja[i] to print whether the user won or lost depending on a correct or incorrect guess respectively.
public static void main(String[] args)
{
int[] caja = new int [5];
caja[0] = 1;
caja[1] = 3;
caja[2] = 5;
caja[3] = 7;
caja[4] = 9;
System.out.println("Mostrando todos los numeros del arreglo");
for (int i = 0; i < caja.length; i++)
{
System.out.println(caja[i]);
}
System.out.println();
int electionGame = 3;
int o = 0;
while(electionGame > 0)
{
Scanner sc = new Scanner(System.in);
int choose = sc.nextInt();
for (int i = 0; i < caja.length; i++)
{
o = o + 1;
if(choose == caja[i])
{
System.out.println("Ganastes");
break;
}
else
{
System.out.println("Perdiestes");
break;
}
}
electionGame--;
}
}
}

Your problem is that you break out of your loop in every case:
if(choose == caja[i])
{
System.out.println("Ganastes");
break;
}
else
{
System.out.println("Perdiestes");
break;
}
Instead of doing this (and printing the result after only the first comparison), you should have a Boolean indicating whether the number was found in the array:
int electionGame = 3;
boolean found = false; //indicates whether user has found right number
while (electionGame > 0 && !found) {
Scanner sc = new Scanner(System.in);
int choose = sc.nextInt();
for (int i = 0; i < caja.length && !found; i++) {
if (choose == caja[i]) {
found = true;
}
}
electionGame--;
if (found) {
System.out.println("you won");
} else {
System.out.println("nope");
}
}
This way, you can check the variable and tell the user whether he won or lost.

Here are some additional suggestions. The answer by Alex (https://stackoverflow.com/a/36133864/6077352) is good. Please note the comments in the code.
import java.util.Scanner;
/** https://stackoverflow.com/q/36133524/6077352 */
public class GuessNumber {
public static void main(String[] args) {
int[] caja = new int[5];
caja[0] = 1;
caja[1] = 3;
caja[2] = 5;
caja[3] = 7;
caja[4] = 9;
System.out.println("Mostrando todos los numeros del arreglo");
for (int i = 0; i < caja.length; i++) {
System.out.println(caja[i]);
}
System.out.println();
int tries = 3;
Scanner sc = new Scanner(System.in);// no need to create scanners in loop
while (tries-- > 0) {// count down tries
System.out.print("Please guess a number... ");
int guess = sc.nextInt();
boolean win = false;// flag to determine if won
for (int i : caja) {// iterate through array and check if guess is inside
win |= (i == guess);// when inside: win=true
}
System.out.println("Answer right? " + win);
System.out.println();
}
}
}

So if the user can attempt to get any of the values of the array you might to change your while loop to this one:
while (electionGame > 0) {
Scanner sc = new Scanner(System.in);
int choose = sc.nextInt();
boolean ganaste = false;
for (int i = 0; i < caja.length; i++) {
o = o + 1;
if (choose == caja[i]) {
ganaste = true;
break;
}
}
if (ganaste)
System.out.println("Ganastes");
else
System.out.println("Perdiestes");
electionGame--;
}

Sorting Java Multidimensional Array

I'm trying to sort the contents of an array and while it seems to be working (no runtime errors; is performing sort tasks), the first 10 rows, while sorted, are not in order with the rest of the rows.
class coordSort.java
import java.io.*;
import java.util.Arrays;
import java.util.Scanner;
public class coordSort {
#SuppressWarnings({ "unchecked", "unused" })
public static void main (String args[]) throws IOException {
String xCoord, yCoord;
int coordSum;
Scanner input = new Scanner(System.in);
//Get x coordinate from user
System.out.print("Enter x coordinate: ");
xCoord = input.next();
//Get x coordinate from user
System.out.print("Enter y coordinate: ");
yCoord = input.next();
boolean sort = false;
char[] a = xCoord.toCharArray();
char[] b = yCoord.toCharArray();
//validate user input is a digit
if ( (Character.isDigit(a[0])) ) {
if(Character.isDigit(b[0]) ){
//digits entered - begin processing all coordinate values
sort = true;
}
}
//If validation failed, inform user
if(!sort){
System.out.println("Please enter a positive numeric value.");
}
if(sort){
//determine SUM of user entered coordinates
coordSum = Integer.parseInt(xCoord) + Integer.parseInt(yCoord);
//define coordinate array
String[][] coordUnsortedArray = new String[26][3];
int counter;
int commaCount;
String xCoordIn, yCoordIn;
int intXCoordIn, intYCoordIn, sumCoordIn, coordDiff;
//define input file
FileInputStream fileIn = new FileInputStream("coords.txt");
BufferedReader reader = new BufferedReader(new InputStreamReader(fileIn));
for (int j = 0; j < coordUnsortedArray.length; j++){
counter = 0;
commaCount = 0;
//line from file to variable
String coordSet = reader.readLine();
//look for the second "," to determine end of x coordinate
for(int k = 0; k < coordSet.length(); k++){
if (coordSet.charAt(k) == ',') {
commaCount++;
counter++;
if (commaCount == 2){
break;
}
}else{
counter++;
}
}
//define x coordinate
xCoordIn = (coordSet.substring(2,(counter - 1)));
intXCoordIn = Integer.parseInt(xCoordIn);
//define y coordinate
yCoordIn = (coordSet.substring((counter),coordSet.length()));
intYCoordIn = Integer.parseInt(yCoordIn);
//coordinate calculations
sumCoordIn = Integer.parseInt(xCoordIn) + Integer.parseInt(yCoordIn);
coordDiff = sumCoordIn - coordSum;
//load results to array
coordUnsortedArray[j][0] = xCoordIn;
coordUnsortedArray[j][1] = yCoordIn;
coordUnsortedArray[j][2] = Integer.toString(coordDiff);
//Output Array (BEFORE SORTING)
//System.out.println((j + 1) + ") " + coordUnsortedArray[j][0] + " : " + coordUnsortedArray[j][1] + " : " + coordUnsortedArray[j][2]);
}
System.out.println("\n");
fileIn.close();
String[][] coordsSorted = new String[26][3];
//Sort array coordDiff, column 3
Arrays.sort(coordUnsortedArray, new ColumnComparator(2));
//Print the sorted array
for(int i = 0; i < coordUnsortedArray.length; i++){
String[] row = coordUnsortedArray[i];
System.out.print((i + 1) + ") ");
for(int j = 0; j < row.length; j++) {
//System.out.print(row[j] + " | ");
coordsSorted[i][j] = row[j];
System.out.print(coordsSorted[i][j] + " : ");
}
System.out.print("\n");
}
}
}
}
class sortCoords.java --
import java.util.Comparator;
#SuppressWarnings("rawtypes")
class ColumnComparator implements Comparator {
int columnToSort;
ColumnComparator(int columnToSort) {
this.columnToSort = columnToSort;
}
//overriding compare method
public int compare(Object o1, Object o2) {
String[] row1 = (String[]) o1;
String[] row2 = (String[]) o2;
//compare the columns to sort
return row1[columnToSort].compareTo(row2[columnToSort]);
}
//overriding compare method
public int compare1(Object o1, Object o2) {
String[] row1 = (String[]) o1;
String[] row2 = (String[]) o2;
//compare the columns to sort
return row1[columnToSort].compareTo(row2[columnToSort]);
}
}
I am trying to sort the array in numerical order by the 3rd column. The unsorted array is populated by a text file containing something like:
a,44,67
b,31,49
c,93,6
I am performing calculations on the array compared to user input and populating the array as follows:
44,67,101
31,49,70
93,6,89
I would like the sortedArray to output the following:
31,49,70
93,6,89
44,67,101

One possible confusion here:
return row1[columnToSort].compareTo(row2[columnToSort])
This is a string comparison, not a numerical one. If you sort based on strings, you will get different results than if you do by numbers - ie "1","10","100","9" vs 1,9,10,100
Check out Integer.parseInt and if you can't figure out the rest, feel free to ask more questions.

As spinning_plate stated. You need to compare their int values i.e. you need a cast there
int num1 = Integer.parseInt(row1[columnToSort]);
int num2 = Integer.parseInt(row2[columnToSort]);
if(num1 > num2)
return 1;
else
return 0;
Place this code in the compareTo method and check. Swap the return statements to sort in reverse order.
Also, adding some error checking in the compareTo method will make the code more efficient.

Ok, so after the assistance provided here, below is the solution that we found. Thanks again for the help everyone! Hopefully the code below helps someone else out.
Code for class1 --
import java.io.*;
import java.util.Arrays;
import java.util.Scanner;
public class coordSort {
#SuppressWarnings({ "unchecked" })
public static void main (String args[]) throws IOException {
String xCoordChar, yCoordChar;
int xCoord, yCoord, coordSum;
Scanner input = new Scanner(System.in);
//Get x coordinate from user
System.out.print("Enter x coordinate: ");
xCoordChar = input.next();
//Get x coordinate from user
System.out.print("Enter y coordinate: ");
yCoordChar = input.next();
boolean sort = false;
char[] a = xCoordChar.toCharArray();
char[] b = yCoordChar.toCharArray();
//validate user input is a digit
if ( (Character.isDigit(a[0])) ) {
if(Character.isDigit(b[0]) ){
//digits entered - begin processing all coordinate values
sort = true;
}
}
//If validation failed, inform user
if(!sort){
System.out.println("Please enter a positive numeric value.");
}
if(sort){
//Parse user input characters to Integers
xCoord = Integer.parseInt(xCoordChar);
yCoord = Integer.parseInt(yCoordChar);
//determine SUM of user entered coordinates
coordSum = xCoord + yCoord;
//define coordinate array
int[][] coordUnsortedArray = new int[26][3];
int counter;
int commaCount;
String xCoordIn, yCoordIn;
int intXCoordIn, intYCoordIn, sumCoordIn, coordDiff;
//define input file
FileInputStream fileIn = new FileInputStream("coords.txt");
BufferedReader reader = new BufferedReader(new InputStreamReader (fileIn));
for (int j = 0; j < coordUnsortedArray.length; j++){
counter = 0;
commaCount = 0;
//line from file to variable
String coordSet = reader.readLine();
//look for the second "," to determine end of x coordinate
for(int k = 0; k < coordSet.length(); k++){
if (coordSet.charAt(k) == ',') {
commaCount++;
counter++;
if (commaCount == 2){
break;
}
}else{
counter++;
}
}
//define x coordinate
xCoordIn = (coordSet.substring(2,(counter - 1)));
intXCoordIn = Integer.parseInt(xCoordIn);
//define y coordinate
yCoordIn = (coordSet.substring((counter),coordSet.length()));
intYCoordIn = Integer.parseInt(yCoordIn);
//coordinate calculations
sumCoordIn = Integer.parseInt(xCoordIn) + Integer.parseInt (yCoordIn);
coordDiff = sumCoordIn - coordSum;
if (coordDiff < 0){
coordDiff = coordDiff * (-1);
}
//load results to array
coordUnsortedArray[j][0] = intXCoordIn;
coordUnsortedArray[j][1] = intYCoordIn;
coordUnsortedArray[j][2] = coordDiff;
}
fileIn.close();
System.out.print("\n");
System.out.println("Array Before Sorting:");
System.out.println("=====================");
//Array Before Sorting
for(int i = 0; i < coordUnsortedArray.length; i++){
int[] row = coordUnsortedArray[i];
System.out.print((i + 1) + ") ");
for(int j = 0; j < (row.length - 1); j++) {
coordUnsortedArray[i][j] = row[j];
if(j < 1){
System.out.print(coordUnsortedArray [i] [j] + ",");
}else{
System.out.println(coordUnsortedArray [i] [j]);
}
}
}
System.out.print("\n");
System.out.print("\n");
//Sort array coordDiff, column 3
Arrays.sort(coordUnsortedArray, new ColumnComparator(2));
System.out.println("Array After Sorting:");
System.out.println("====================");
//Original Array After Sorting
for(int i = 0; i < coordUnsortedArray.length; i++){
int[] row = coordUnsortedArray[i];
System.out.print((i + 1) + ") ");
for(int j = 0; j < (row.length - 1); j++) {
coordUnsortedArray[i][j] = row[j];
if(j < 1){
System.out.print(coordUnsortedArray[i][j] + ",");
}else{
System.out.println(coordUnsortedArray [i] [j]);
}
}
}
}
}
}
Code for class2 --
import java.util.Comparator;
#SuppressWarnings("rawtypes")
class ColumnComparator implements Comparator {
int columnToSort;
ColumnComparator(int columnToSort) {
this.columnToSort = columnToSort;
}
//Compare method
public int compare(Object o1, Object o2) {
int[] row1 = (int[]) o1;
int[] row2 = (int[]) o2;
int intRow1 = (row1[columnToSort]);
int intRow2 = (row2[columnToSort]);
return new Integer(intRow1).compareTo(new Integer(intRow2));
}
}

matrix manipulation in java OOP

This code gives me errors at lines 153, 158 and 163 stating"variables not found". i need to print them using the menu but not sure if this is working. help would be appreciated.
import java.io.*;
import java.util.*;
class Matrix {
double[][] element;
int rows, cols;
Matrix(int rows, int cols) {
this.rows = rows;
this.cols = cols;
element = new double[rows][cols];
}
public double getValue(int row, int col) {
return element[row][col];
}
public void setValue(int row, int col, double value) {
element[row][col] = value;
}
public int getNoRows() { // returns the total number of rows
return rows;
}
public int getNoCols() { // returns the total number of cols
return cols;
}
// The methods for the main calculations
public Matrix AddMatrix(Matrix m2) {
int row1 = getNoRows();
int col1 = getNoCols();
Matrix result = new Matrix(row1, col1);
for (int i = 0; i < row1; i++) {
for (int j = 0; j < col1; j++) {
result.setValue(i, j, this.getValue(i, j) + m2.getValue(i, j));
}
}
return result;
}
public Matrix MultiplyMatrix(Matrix m2) {
if (this.getNoCols() != m2.getNoRows()) {
throw new IllegalArgumentException("matrices can't be multiplied");
}
int row2 = this.getNoRows();
int col2 = m2.getNoCols();
Matrix result = new Matrix(row2, col2);
for (int i = 0; i < row2; i++) {
for (int j = 0; j < col2; j++) {
result.setValue(i, j, result.getValue(i, j) + this.getValue(i, j) * m2.getValue(i, j));
}
}
return result;
}
public Matrix TransposeMatrix() {
int row3 = this.getNoCols();
int col3 = this.getNoRows();
Matrix result = new Matrix(row3, col3);
for (int i = 0; i < row3; i++) {
for (int j = 0; j < col3; j++) {
result.setValue(i, j, this.getValue(j, i));
}
}
return result;
}
public void DisplayMatrix() {
for (int i = 0; i < this.getNoRows(); i++) {
for (int j = 0; j < this.getNoCols();
j++) {
System.out.print((this.getValue(i, j)) + " ");
}
System.out.print("\n");
}
System.out.print("\n");
}
}
public class Lab1 {
public static void main(String args[]) throws FileNotFoundException {
int choice;
Scanner in = new Scanner(System.in);
Boolean loopcont= true;
while (loopcont){
System.out.println("1. Add two matrices \n");
System.out.println("2. Multiplymatrix two matrices \n");
System.out.println("3. Take transpose of a matrix \n");
System.out.println("4. Display a matrix \n");
System.out.println("5. Exit \n");
System.out.println("Enter your choice \n");
choice = in.nextInt();
switch (choice) {
case 1:{
System.out.println("For the first matrix");
Matrix m1 = MatrixReader();
m1.DisplayMatrix();
System.out.println("For the second matrix");
Matrix m2 = MatrixReader();
m2.DisplayMatrix();
Matrix m3 = new Matrix(m1.getNoRows(), m1.getNoCols());
m3 = m1.AddMatrix(m2);
m3.DisplayMatrix();
break ;
}
case 2:{
System.out.println("For the first matrix");
Matrix m1 = MatrixReader();
m1.DisplayMatrix();
System.out.println("For the second matrix");
Matrix m2 = MatrixReader();
m2.DisplayMatrix();
Matrix m3 = new Matrix(m1.getNoRows(), m2.getNoCols());
m3 = m1.MultiplyMatrix(m2);
m3.DisplayMatrix();
break;
}
case 3:{
System.out.println("For the first matrix");
Matrix m1 = MatrixReader();
m1.DisplayMatrix();
Matrix m3 = new Matrix(m1.getNoRows(), m1.getNoCols());
m3 = m1.TransposeMatrix();
m3.DisplayMatrix();
break;
}
case 4:{
int printInput;
System.out.println("What matrix do you want to print?");
printInput = in.nextInt();
switch(printInput){
case 1:{
System.out.println("Printing Matrix m1");
m1.DisplayMatrix();
break;
}
case 2:{
System.out.println("Printing Matrix m2");
m2.DisplayMatrix();
break;
}
case 3:{
System.out.println("Printing Matrix m3");
m3.DisplayMatrix();
break;
}
default:{
System.out.println("Invalid Input. please enter again");
break;
}
}
}
case 5:{
loopcont= false;
break;
}
default:{
System.out.println("Incorrect input. Kindly enter again \n");
break;
}
}
}
}
public static Matrix MatrixReader() throws FileNotFoundException {
System.out.println("Give the filename for the matrix");
Scanner filescanner = new Scanner(System.in);
Scanner scanner = new Scanner(new File(filescanner.nextLine()));
scanner.nextLine(); // removes the first line in the input file
String rowLine = scanner.nextLine();
String[] arr = rowLine.split("=");
int rows = Integer.parseInt(arr[1].trim());
String colLine = scanner.nextLine();
String[] arr2 = colLine.split("=");
int cols = Integer.parseInt(arr2[1].trim());
Matrix test = new Matrix(rows, cols);
for (int i = 0; i < rows; i++) {
for (int j = 0; j < cols; j++) {
test.setValue(i, j, scanner.nextDouble());
}
}
return test;
}
}

EDIT:
Under Case 4: variables m1, m2, m3 are not initialized.
Matrix m1;
Matrix m2;
Matrix m3;
switch (choice) {
case 1: {
System.out.println("For the first matrix");
m1 = MatrixReader();
m1.DisplayMatrix();
System.out.println("For the second matrix");
m2 = MatrixReader();
m2.DisplayMatrix();
m3 = new Matrix(m1.getNoRows(), m1.getNoCols());
m3 = m1.AddMatrix(m2);
m3.DisplayMatrix();
break;
}
case 2: {
System.out.println("For the first matrix");
m1 = MatrixReader();
m1.DisplayMatrix();
System.out.println("For the second matrix");
m2 = MatrixReader();
m2.DisplayMatrix();
m3 = new Matrix(m1.getNoRows(), m1.getNoCols());
m3 = m1.MultiplyMatrix(m2);
m3.DisplayMatrix();
break;
}
case 3: {
System.out.println("For the first matrix");
m1 = MatrixReader();
m1.DisplayMatrix();
m3 = m1.TransposeMatrix();
m3.DisplayMatrix();
break;
}
case 4: {
int printInput;
System.out.println("What matrix do you want to print?");
printInput = in.nextInt();
switch (printInput) {
case 1: {
System.out.println("Printing Matrix m1");
m1 = MatrixReader();
m1.DisplayMatrix();
break;
}
case 2: {
System.out.println("Printing Matrix m2");
m2 = MatrixReader();
m2.DisplayMatrix();
break;
}
case 3: {
System.out.println("Printing Matrix m3");
m3 = new Matrix(m1.getNoRows(), m1.getNoCols());
m3.DisplayMatrix();
break;
}
default: {
System.out.println("Invalid Input. please enter again");
break;
}
}
}
case 5: {
loopcont = false;
break;
}
default: {
System.out.println("Incorrect input. Kindly enter again \n");
break;
}
}

If you tired to write your own code with matrix, just download library I developed. It can add, multiply, invert, transpond, calculate determinant and solve linear systems.
please check: Linear Math Library
This is open source you can download the source code too and look how in works.