How do I add numbers in a text file array to a 2d int array?

Question

I made a 2d array chart that shows and calculates the average noise levels of each car model as my school project. Now I need to have a separate file to store my array values and put them in the chart. I've tried to add the values in using a while loop but it gives me this error. How can I add values from my text file to the array? I am still new to java.

public static void writetoarray(){
 try{
    k = new Scanner(new File("test.txt"));

 }
catch(Exception e){
System.out.println("You got an error");
}
 int i = 0;
 while(k.hasNextInt()){
    firstarray[0][i] = k.nextInt();
    firstarray[1][i] = k.nextInt();
    firstarray[2][i] = k.nextInt();
    firstarray[3][i] = k.nextInt();
    firstarray[4][i] = k.nextInt();
    firstarray[5][i] = k.nextInt();
    firstarray[6][i] = k.nextInt();
    i++;
    }
  }


"Exception in thread "main" java.lang.NullPointerException
 at practice.writetoarray(practice.java:29)
 at practice.main(practice.java:11)"

This is my whole code:

import java.io.File;
import java.util.*;
public class practice {
public static Scanner k;
public int foo = Integer.parseInt(k.next());    
public static int n = 1;
public static int firstarray[][] ={{81,90,92,103,111,121,132,0},
{78,85,90,99,104,111,118,0},{80,86,91,95,100,108,119,0},
{87,90,95,101,111,121,133,0},{66,70,76,86,96,115,125,0},
{81,83,85,93,102,113,122,0},{76,78,80,85,94,104,114,0},{0,0,0,0,0,0,0,0}};
public static int y = 0;    
public static void main(String[] args) {
    String tableheadings[][]={{"\t\t\t\t    MPH"+"                              
|"},{"Model|","20","30","40","50","60","70","80","Avg     |",},
{"_____________________________________
___________________________________|"}};


writetoarray();
displayheader(tableheadings);
countArraytotal(firstarray);
arrayavg(firstarray);
arrayavgc(firstarray);
printrows(firstarray);
countRowandCol(firstarray);
}


 public static void writetoarray(){
 try{
    k = new Scanner(new File("test.txt"));

 }
catch(Exception e){
System.out.println("You got an error");
}
 int i = 0;
 while(k.hasNextInt()){
    firstarray[0][i] = k.nextInt();
    firstarray[1][i] = k.nextInt();
    firstarray[2][i] = k.nextInt();
    firstarray[3][i] = k.nextInt();
    firstarray[4][i] = k.nextInt();
    firstarray[5][i] = k.nextInt();
    firstarray[6][i] = k.nextInt();
    i++;
   }

 }



 public static void displayheader(String a[][]){
    for (int row=0 ;row<a.length;row++){
        for(int column=0; column<a[row].length;column++){
        System.out.print(a[row][column]+"\t");
        }
    System.out.println();
}
}

public static void printrows(int a[][]){

for (int row=0 ;row<a.length;row++){
    if(row<a.length-1){
    System.out.print(n+++"    |\t");
    }
    else{System.out.print("Avg  |\t");}
    for(int column=0; column<a[row].length;column++){

        System.out.print(a[row][column]+"\t");

    }

    System.out.print("|");
    System.out.println();
 }
}

public static void arrayavg(int[][] array) {
int s=   0;
for (int i = 0; i < array.length; i++){ s=0;
for (int j = 0; j < array[i].length; j++){             
s += array[i][j];
}
firstarray[i][7] = Math.round(s/(array.length-1));  
 }
}

public static void arrayavgc(int[][] array) {
int s=   0;

for (int i = 0; i < array.length; i++){ s=0;
for (int j = 0; j < array[i].length; j++){             
s += array[j][i];
}
firstarray[7][i] = Math.round(s/(array[i].length-1));
}
}

public static void countArraytotal(int[][] table){
int total=0;

for (int row=0;row<table.length;row++)
for (int col=0;col<table[0].length;col++)
  total += table[row][col];
firstarray[7][7]=Math.round(total/49);
}

public static void countRowandCol(int[][] array){
int rowsize = array.length;
int columnSize = array.length;
System.out.println("There are " + rowsize + " rows and " + columnSize+ " 
columns in this table.");

}
}

Also, ignore the values I already have in my array.

Possible duplicate of Java serialization of multidimensional array — EJoshuaS - Stand with Ukraine
– EJoshuaS - Stand with Ukraine, Commented May 31, 2017 at 18:56
It looks like the value in the file is more than the size of the array i.e why you are getting NullPointerException. — Hamza Anis
– Hamza Anis, Commented May 31, 2017 at 18:59
Other possible duplicate: What is a NullPointerException and how do I fix it? — EJoshuaS - Stand with Ukraine
– EJoshuaS - Stand with Ukraine, Commented May 31, 2017 at 19:00
in the test.txt is just a couple numbers to test the program: 1 2 3 4 5 6 7 — urmomscarrot
– urmomscarrot, Commented Jun 1, 2017 at 18:00

EJoshuaS - Stand with Ukraine · Accepted Answer · 2017-05-31 19:17:37Z

One problem I notice is here:

try{
    k = new Scanner(new File("test.txt"));
 }
catch(Exception e){
    // You really should print out the full exception details here
    // It'll make debugging much easier
    System.out.println("You got an error");
}

// If you keep going after an exception here, you'll get a NullPointerException
// because k isn't initialized validly
int i = 0;
while(k.hasNextInt()){
    firstarray[0][i] = k.nextInt();
    firstarray[1][i] = k.nextInt();
    firstarray[2][i] = k.nextInt();
    firstarray[3][i] = k.nextInt();
    firstarray[4][i] = k.nextInt();
    firstarray[5][i] = k.nextInt();
    firstarray[6][i] = k.nextInt();
    i++;
}

If there's an exception when you try to initialize k, then you can't use it because it won't actually have been created.

Also, rather than printing out "You got an error" in the case when there's an exception, I strongly suggest printing out the full exception details (e.toString() will print out the exception message and stack trace). Obviously, you wouldn't want to display that to users in an actual production system, but for learning purposes it makes debugging a lot easier if you display (or at least log) the full details. (In production systems, we usually create a log of some kind with the full details of an exception like this so that we can debug more easily).

Collectives™ on Stack Overflow

How do I add numbers in a text file array to a 2d int array?

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related