Develop Reference

How to order an array/list of int that is received as a string by input in Java

I was trying to test my skills and I try to do a test.
I receive the following input:
[7,11,10,6,9]
[21,24,25,23,26]
[116,115,117,120,121,119]
I need to sort all these values.
I try to do the following:
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String[] parts = null;
List<String> linhas = new ArrayList<>();
for (int i = 0; i < 3; i++) {
String line = br.readLine();
line = line.replace("[","");
line = line.replace("]","");
line = line.replace(" ","");
System.out.println(line);
parts = line.split(",");
}
This way I got to show the output
7,11,10,6,9
21,24,25,23,26
116,115,117,120,121,119
The "String[parts]" got all values, but I don't know how to sort it, because the "parts" parameter is inside a "for loop".
How can I convert it to int/Integer and sort each line?

Assuming [7,11,10,6,9] be the input, we can try converting to a list of integers, and then sort that list:
String input = "[7,11,10,6,9]";
input = input.replaceAll("\\[(.*)\\]", "$1");
String[] vals = input.split(",");
List<Integer> output = Arrays.stream(vals)
.map(v -> Integer.parseInt(v))
.collect(Collectors.toList());
Collections.sort(output);
System.out.println(Arrays.toString(output.toArray()));
This prints:
[6, 7, 9, 10, 11]

Once you have parts you must convert this String[] into an int[]. To do this, first create an int[] for your results to go in. It must be the same size as your String[]:
int[] ints = new int[parts.length];
Then, iterate through the String[] and fill in values in the int[]:
for (int i = 0; i < parts.length; i++) {
ints[i] = Integer.parseInt(parts[i]); // converts a string containing an integer into its int value
}
Finally, to sort each line, a simple call to Arrays.sort(ints); will sort your array of integers.
Bonus:
This can be achieved more cleanly in a single line using Java 8 Streams, as follows:
List<Integer> sortedInts = Arrays.stream(parts).map(Integer::parseInt).sorted().collect(Collectors.toList());

You can do the replace() lines at once and split more cleanly with a regex:
parts = line.split("[\\[\\], ]+");
and use the Iterable technique that cameron1024 demonstrates in his answer. I think that using Iterable is a better choice for this use case than using Streams because the input size is trivially small and Streams has to spend more time to spin up.
The whole thing would look like:
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String[] parts;
List<String> linhas = new ArrayList<>();
for (int i = 0; i < 3; i++) {
String line = br.readLine();
parts = line.split("[\\[\\] ,]+");
}
int ints[] = new int[parts.length];
for(int i = 0; i < parts.length; i++){
ints[i] = Integer.parseInt(parts[i]);
}
Arrays.sort(ints);

CSV input to two dimmensional array in java

I have a read() method and inside I want to separate the Strings(which have spaces between them) and putting them in a two dimensional array, but before that I get rid of all the spaces. After the array initialized, it is given to the CSV constructor and that is creating its own 2D array.
The problem is that I always get the following error: "variable sr might not have been initialized" at CSV csv = new CSV(sr).
How do I make sure that my array gets the valid String?
private String[][] tomb;
private CSV(String[][] t2) {
tomb = new String[t2.length][];
for(int i = 0; i < t2.length; i++) {
tomb[i] = new String[t2[i].length];
for(int j = 0; j < t2[i].length; j++) {
tomb[i][j] = t2[i][j];
}
}
}
public static CSV read(Scanner sc) {
String[][] sr;
int n = 0;
while (sc.hasNextLine())
{
String line = sc.nextLine();
String[] str = line.split(",");
sr = new String[str.length][];
for (int i = 0; i < str.length; i++) {
sr[i][n].replaceAll("\\s+","");
}
n++;
}
CSV csv = new CSV(sr);
return csv;
}

You can resolve the error by setting sr to null in the initialization:
String[][] sr = null;
If you want to make sure sr was set correctly, you can check if sr is still null after the while loop completes.

null pointer exception string builder

I am trying to use the setCharAt method in a StringBuilder but I am getting a null pointer exception. Is there a way I can add values to the StringBuilder array I have made so I wont get these error.
From research I have found the .append() method but I'm not even sure how it works.
import java.util.*; // Allows for the input of a scanner method.
import java.io.*; // Allows for the inputting and outputting of a data file.
import java.lang.*; // Allows for the use of String Methods.
//////////////////////////////////////////////////////////////////////////////////////
public class TESTY
{
static Scanner testanswers;
static PrintWriter testresults;
public static void main(String[] args) throws IOException
{
testanswers = new Scanner(new FileReader("TestInput.dat"));
testresults = new PrintWriter("TestOutput.dat");
String StudentID;
String answers;
// Reads first two lines first to know how many records there are.
String answerKey = testanswers.nextLine();
int count = Integer.parseInt(testanswers.nextLine());
// Allocate the array for the size needed.
String[][] answerArray = new String[count][];
for (int i = 0; i < count; i++)
{
String line = testanswers.nextLine();
answerArray[i] = line.split(" ", 2);
}
for(int row = 0; row < answerArray.length; row++)
{
for(int col = 0; col < answerArray[row].length; col++)
{
System.out.print(answerArray[row][col] + " ");
}
System.out.println();
}
gradeData(answerArray, answerKey);
testanswers.close();
testresults.close();
}
///////////////////////////////////////////////////////////
//Method: gradeData
//Description: This method will grade testanswers showing
//what was missed, skipped, letter grade, and percentage.
///////////////////////////////////////////////////////////
public static double gradeData(String[][] answerArray, String answerKey)
{
String key = answerKey;
double Points = 0;
StringBuilder[] wrongAnswers = new StringBuilder[5];
String studAnswers;
for(int rowIndex = 0; rowIndex < answerArray.length; rowIndex++) /// Counting rows
{
studAnswers = answerArray[rowIndex][1].replace(" ", "S"); ///Counts rows, Col stay static index 1
for(int charIndex = 0; charIndex < studAnswers.length(); charIndex++)
{
if(studAnswers.charAt(charIndex) == key.charAt(charIndex))
{
Points += 2;
}
else if(studAnswers.charAt(charIndex) == 'S')
{
Points --;
}
else if(studAnswers.charAt(charIndex) != key.charAt(charIndex))
{
for(int i = 0; i < wrongAnswers.length; i++)
{
wrongAnswers[i].setCharAt(charIndex, 'X');
}
Points -= 2;
}
}
System.out.println(Points);
}
return Points;
}
}
The error is occurring on line 91 :
wrongAnswers[i].setCharAt(charIndex, 'X');

You have declared an array of StringBuilders, but you haven't initialized any of the slots, so they're still null.
Initialize them:
StringBuilder[] wrongAnswers = new StringBuilder[5];
for (int i = 0; i < wrongAnswers.length; i++)
{
wrongAnswers[i] = new StringBuilder();
}
Additionally, using setCharAt won't work here, because initially, there is nothing in the StringBuilder. Depending on what you want here, you may need to just call append, or you may initially want a string full of spaces so that you can set a specific character to 'X'.

StringBuilder[] wrongAnswers = new StringBuilder[5];
does not create 5 empty StringBuilders but 5 null StringBuilders.
You need to call something like
wrongAnswers[i] = new StringBuilder()
in order to initialize your 5 array members.

Your problem is that
StringBuilder[] wrongAnswers = new StringBuilder[5];
does not create 5 StringBuilder objects. It only creates an array with 5 null StringBuilder references. You need to create each StringBuilder separately with a line such as
wrongAnswers[i] = new StringBuilder();
inside a loop over i.

extract data from csv file and put to 2D Array - refactoring

I need read data from csv file and much more convinience for me is put there to 2D array (to my mind it's easiest way to work with this "schedule" data).
Each file line contained information in following format:
Instructor, Course, Group, Student, Result
as follows example:
Paul Schwartz,Introduction to Computer Architecture,I1,Ben Dunkin,88
Muhamed Olji,Object Oriented Programming,I4,Mike Brown,73
But my code needs some simplify. But I don't know how to make it easier and ask of You.
Code:
private String[][] fileContent(String pathToCSVFile) {
final int ROWS = 100;
final int COLUMNS = 5;
String fileData[][] = new String[ROWS][COLUMNS];
Scanner scanner = new Scanner(pathToCSVFile);
boolean done = false;
int i, j;
while (!done) {
for (i = 0; i >= 0; i++) {
for (j = 0; j >= 0; j++) {
String str[] = scanner.nextLine().split(",");
for (int element = 0; element < str.length; element++) {
fileData[i][element] = str[element];
if (i >= ROWS) {
Arrays.copyOf(fileData, fileData.length * 2);
}
}
}
}
if (!scanner.hasNextLine()) done = true;
}
return fileData;
}
How to refactor this snippet of code for better simplicity?
Does exist any better way for partially filled array (than Arrays.copyOf(fileData, fileData.length * 2))?

Using openCSV, you can get a list containing all the lines and convert it to an array (or just keep the list):
try (CSVReader reader = new CSVReader(new BufferedReader(
new FileReader(pathToCSVFile)));) {
List<String[]> lines = reader.readAll();
return lines.toArray(new String[lines.size()][]);
}
(using Java 7 try-with-resources syntax)

First of all, be careful with those for loops. They are "almost" undefined loops, because they start with i,j=0, and loop while >=0 (always, until they overflow into a negative number).
And why do you need them anyway? I think with you while and the for(element) you are done, right?
Something like that (I didn't tried, is just to explain the concept)
private String[][] fileContent(String pathToCSVFile) {
final int ROWS = 100;
final int COLUMNS = 5;
String fileData[][] = new String[ROWS][COLUMNS];
Scanner scanner = new Scanner(pathToCSVFile);
boolean done = false;
int i=0;
while (!done) {
String str[] = scanner.nextLine().split(",");
for (int element = 0; element < str.length; element++) {
fileData[i][element] = str[element];
if (i >= ROWS) {
Arrays.copyOf(fileData, fileData.length * 2);
}
}
if (!scanner.hasNextLine())
done = true;
else
i++;
}
return fileData;
}
By the way, why don't you use objects, like an ArrayList? It would make your life easier, so you don't have to worry about memory handling. You just add new objects.
Something like an ArrayList <ArrayList <String>>

List<String> ----> to int [ ] [ ] arr

Well I have been stumped as to the best way to do this, I have written the code to read in lines of code from txt files as List. I can then print specific parts or convert this to an array of objects. But, ultimately I would like to have just a 2d int array you can see often in C/C++. I am very green when it comes to java, having only started earlier this week. I have like it up until this point of making dynamic 2d arrays at run time. Can any of you suggest a good way to get to a 2d int array from where i am currently stuck. I was just about to convert it to a char array using 'toChar', then to take the (value#index-48) and store it in its corresponding spot, but that seems pretty ghetto to me.
====updated==========================
eh, thanks for all the replies, but I just figured out how to do it using doubles, so for anyone else, here you go. I would still rather have int, since I have already built my other matrixops classes using this type, but Double shouldn't be an issue i guess.
package uaa.cse215;
import java.io.*;
import java.util.*;
public class ReadMatrix {
private Double[][] A;
private Double[][] B;
private int count;
public int filedir(String matrix) throws Exception{
Double[][] Temp;
String[] arr;
BufferedReader rd = new BufferedReader(new FileReader(matrix));
String s;
List<String> textFile = new ArrayList<String>();
while ((s=rd.readLine())!=null) {
textFile.add(s);
}
String splitarray[] = textFile.get(0).split(" ");//run once to grab # cols
int rows = textFile.size();//number of rows
int cols = splitarray.length;//number of cols
Temp = new Double[rows][cols]; // now can initiate array
for (int i=0; i<rows; i++) {
s = textFile.get(i);
arr = s.split(" ");
for (int j=0; j<cols; j++) {
Temp[i][j] = Double.parseDouble(arr[j]);
}
}
count++;
if (count == 1){
A = Temp;
}
else
B = Temp;
rd.close();
return(1);
}
}

Please note that Java has the char data type which is a 16bit unsigned integer holding a UTF-16 code point. int is in Java always a signed 32 bit integer. So if you want a C like Arrays of chars representing the content of a String, you should use a char[][]
To convert the content of your List<String> into a 2d array you can use the following code:
char[][] twoDarray = new char[textFile.size()];
for(int i = 0; i < textFile.size(); i+)
{
twoDarray[i] = textFile.get(i).toCharArray();
}
The array twoDarray then contains all Strings each as a char array.

This line won't compile
splitarray[j] = textFile.get(i).split(" ");
as splitarray[j] is of type String and split returns an array of Strings
Do the following instead:
for(int row=0;row<textFile.size();row++){
String[] splitarray = textFile.get(row).split(" ");
for(int col=0;col<splitarray.length;col++){
tmp[row][col] = Integer.parse(splitarray[col]);
}
}

if the input matrix dimentions are dynamic or jagged you can use
List<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();
to read numbers and than copy it to raw 2d array if you want.
java.util.Scanner has many handy methods for reading "typed" data from input
Here's an example reading file to 2D array
public static int[][] read2DArray(String fileName) throws FileNotFoundException {
Scanner sc = null;
List<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();
int columnCount = 0;
int[][] arr = null;
try {
sc = new Scanner(new File(fileName));
while (sc.hasNextLine()) {
// Read line
String line = sc.nextLine();
// Split it
String[] nums = line.split(" ");
if (nums.length > columnCount) {
columnCount = nums.length;
}
// Convert to integers and add to list
list.add(new ArrayList<Integer>());
for (String n : nums) {
list.get(list.size() - 1).add(new Integer(n));
}
}
// Convert list to array
int rowCount = list.size();
arr = new int[rowCount][columnCount];
for (int i = 0; i < rowCount; i++) {
for (int j = 0; j < list.get(i).size(); j++) {
arr[i][j] = list.get(i).get(j);
}
}
} finally {
if (sc != null) {
sc.close();
}
}
return arr;
}

Assuming your data file contains ascii-represented numbers that you want parsed into integers:
11 -9 13
12 55 102
1 1 1024
Then you can use the Integer(String s) constructor to parse your string objects.
Also, I suggest splitting each row only once. It won't matter much for small arrays, but the larger your inputs get, the more you'll needlessly recompute the splits.
An (untested) re-writing:
int tmp[][] = new int [rows][cols];
for(int i=0;i<rows;i++){
splitarray = textFile.get(i).split(" ");
for(int j=0;j<cols;j++){
tmp[i][j] = Integer(splitarray[j]);
}
}