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Java File Problems

So we want an application to allow the user to enter the names and grades of students the user should be prompted for the name of the file to create and for the number of students to be entered (1 grade per student). Then the program takes all of the grades and averages them. The problem is that it is not reading the file and always gives us a average of -0.0.
`
public static void main(String[] args) throws IOException {
System.out.println("What is the name of the file you would like to create?");
filename = p.next();
File fd = new File(filename + ".txt");
fd.createNewFile();
students(fd);
}
public static void students(File fd) throws IOException {
int numbstudents;
FileWriter ap = new FileWriter(fd, true);
BufferedWriter ad = new BufferedWriter(ap);
System.out.println("How many students would you like to add?");
numbstudents = p.nextInt();
int i = 0;
while (i != numbstudents) {
for (i = 0; i < numbstudents; i++) {
System.out.println("What is the name of student number " + i + " ?");
String name = p.next();
ad.write(name);
ad.newLine();
System.out.println("What grade did student number " + i + " acheive?");
String a = f.next();
ad.write(a);
ad.newLine();
}
}
read(fd);
ad.close();
}
public static void read(File fd) throws FileNotFoundException {
int counter = 0;
FileReader h;
BufferedReader g;
String test;
double average, total = 0;
int number = 0;
int i = 0;
try {
h = new FileReader(fd);
g = new BufferedReader(h);
while ((test = g.readLine()) != null) {
number += 1;
System.out.println(test);
counter = counter + 1;
i = counter % 2;
if (i == 0) {
total += Double.parseDouble(test);
}
}
average = total / (number - 1);
System.out.println("The students average is: " + average);
g.close();
fd.delete();
} catch (FileNotFoundException e) {
System.out.println("File could not be found.");
} catch (IOException e) {
System.out.println("Your file could not be read.");
}
}
}
`

You're attempting to read from the file before you've closed the writer.
The close() call includes flushing buffered data to disk. You're reading before data is flushed to disk.
As a side note, consider what you're accomplishing with this pair of statements:
while (i != numbstudents) {
for (i = 0; i < numbstudents; i++) {
The while is unnecessary. The for statement iterates over the comfortably numb students.
Also note the difference in conditions between the two. In general, when iterating over numbers, it's safer to use '<', '<=', '>' or '>=' than '==' or '!='. Otherwise, if you pass by the endpoint before an equality condition, it will continue happily past the end.
Finally, consider naming your methods with descriptive verb phrases. This will help you with breaking the big problem down into smaller pieces. For example, you could have one method called inputStudents() that reads input and creates and closes the file, called before another method printAverageOfStudents() that reads the file and computes the average.

How to prime multiple blank records and then add data to them

I've been struggling trying to understand this area in java, so I figured perhaps someone online could help with it. Basically, I need to "prime" 9,000 blank records (for a bank) and then choose to enter data in specific areas (i.e. account number, name, balance).
I know I have to use for loops but I don't know where they should go. Currently, I can create 9,000 records, but after entering data for one record it just duplicates 9,0000 times, instead of putting the record in one specific spot and leaving the rest blank.
import java.nio.file.*;
import java.io.*;
import static java.nio.file.StandardOpenOption.*;
import java.util.Scanner;
public class WriteEmployeeFile
{
public static void main(String[] args)
{
Scanner input = new Scanner(System.in);
File myFile = new File ("C:\\Users\\USSI\\Desktop\\CustomerRecords.txt");
Path file = Paths.get("C:\\Users\\USSI\\Desktop\\CustomerRecords.txt");
String s = "000, ,00.00" +
System.getProperty("line.separator");
String delimiter = ",";
int account;
String name;
double balance;
final int QUIT = 999;
final int MAX = 9001;
try
{
OutputStream output = new
BufferedOutputStream(Files.newOutputStream(file, CREATE));
BufferedWriter writer = new
BufferedWriter(new OutputStreamWriter(output));
System.out.print("Enter client account number: ");
account = input.nextInt();
while(account != QUIT)
{
System.out.print("Enter last name for client #" +
account + ": ");
input.nextLine();
name = input.nextLine();
System.out.print("Enter account balance: ");
balance = input.nextDouble();
s = account + delimiter + name + delimiter + balance;
for(int count = 0; count < MAX; ++count)
writer.write(s, 0, s.length());
writer.newLine();
System.out.print("Enter next ID number or " +
QUIT + " to quit: ");
account = input.nextInt();
}
writer.close();
}
catch(Exception e)
{
System.out.println("Message: " + e);
}
}
}
EDIT: These are my assignment instructions (if someone was curious or if I didn't explain it clearly.
The Winter Park Bank maintains customer records in a random access file. Write an application that creates 9,000 blank records and then allows the user to enter customer account information, including an account number that is 9999 or less, a last name, and a balance. Insert each new record into a data file at a location that is equal to the account number. Assume that the user will not enter invalid account numbers. Force each name to eight characters, padding it with spaces or truncating it if necessary. Also assume that the user will not enter a bank balance greater than 99,000.00. Save the file as WinterParkBankFile.java.

Not sure what you want, but to give the idea of instantinating 9000 bank accounts and then access them by their place in the list they are put:
class BankAccount {
int number;
int balance;
String name;
public static void main(String[] args) {
List<BankAccount> accounts = new ArrayList<BankAccount>();
for (int i = 0; i < 9000; i++) {
accounts.add(new BankAccount());
}
// fill these variables from console however you want
int i = 0;
int balanceReadFromConsole = 0;
int numberReadFromConsole = 0;
accounts.get(i).name = "Whatever you want to set as the i-th account's name";
accounts.get(i).balance = balanceReadFromConsole;
accounts.get(i).number = numberReadFromConsole;
}
}

Coin flip game save issue

I am creating a coin flip game for an assignment that saves your last high score and name. the program works fine if there is not a high score file already there, but if there is a file there the program stops working.
import java.util.Scanner;
import java.io.File;
import java.io.FileWriter;
import java.io.PrintWriter;
public class BradySkuza43
{
public static void main( String[] args ) throws Exception
{
Scanner keyboard = new Scanner(System.in);
String coin, again, bestName, saveFile = "coin-flip-score.txt";
int flip, streak = 0, best;
File in = new File(saveFile);
if ( in.createNewFile() )
{
System.out.println("Save game file doesn't exist. Created.");
best = 1;
bestName = " ";
}
else
{
Scanner input = new Scanner(in);
bestName = input.next();
best = input.nextInt();
input.close();
System.out.println("High score is " + best + " flips in a row by " + bestName );
}
do
{
flip = 1 + (int)(Math.random()*2);
if ( flip == 1 )
{
coin = "HEADS";
}
else
{
coin = "TAILS";
}
System.out.println( "You flip a coin and it is... " + coin );
if ( flip == 1 )
{
streak++;
System.out.println( "\tThat's " + streak + " in a row...." );
System.out.print( "\tWould you like to flip again (y/n)? " );
again = keyboard.next();
}
else
{
streak = 0;
again = "n";
}
} while ( again.equals("y") );
System.out.println( "Final score: " + streak );
if ( streak > best )
{
System.out.println("That's a new high score!");
System.out.print("Your name: ");
bestName = keyboard.next();
best = streak;
}
else if ( streak == best )
{
System.out.println("That ties the high score. Cool.");
}
else
{
System.out.println("You'll have to do better than " + streak + "if you want a high score.");
}
PrintWriter out = new PrintWriter( new FileWriter(saveFile) );
out.println(bestName);
out.println(best);
out.close();
}
}
when there is a file already there I get a NoSuchElement error. I am assuming it has to do with the import functions but I am unaware of how to fix it.

The way you read 'best' when there is already a file (with the 'best' value) seems to be incorrect. You may be looking for something like this (modify based on your data) to read the 'saved best value'.
BufferedReader reader = new BufferedReader(new FileReader(in));
String readNumber = "";
while (reader.readLine() != null) {
readNumber += reader.readLine();
}
best = Integer.valueOf(readNumber);

Ended up having to just run the code to see how the savefile is being produced. Seeing that NoSuchElement exception is coming from the second read from the file (input.nextInt()) pointed to the problem.
If you don't beat the existing the streak (including getting TAILS as your first flip), you aren't prompted for a name. This makes the savefile read
\n
1
\n
Scanner by default ignore whitespace. You don't check if there is available input (hasNext methods). When you call the next() or nextInt() when there is no input you get NoSuchElement. Why is this happening from the save?
Line by line:
bestName = input.next(); <-- This is getting the "1" since there is a name saved
best = input.nextInt(); <-- since the 1 was already read, so there's nothing to get
That second input with the savefile after getting an initial TAILS, is causing your crash.
Two solutions, make sure you are getting and saving the bestName in the else at the end of your main, or be more careful in reading the savefile.
(edit)
In general when using Scanner (or just about anything API that has a the hasNext()/next() style), it's best to call and check hasNext() before each next(). This will ensure you have something to get from the next().
Even if you don't think there is a possible reason for there not to be something there, having something like
if(!foo.hasNext) {
System.out.println("foo should really have something here, but hasNext says it doesn't);
System.exit();
}
will stop your code in its tracks if there is a problem, and give you a stop to add some debug statements to see what's going on.

Here are some suggestions:
Your high score file's name doesn't change, right? It shouldn't be a variable, it should be a static final variable.
Play the game and then decide whether or not this is a high score. So you should have a getHighScore() method (which can be static).
If the new score is a high score, then write it to the high score file. There should be a method static writeHighScore(final String name, final int score).
So I would change your program to something more like this:
public class BradySkuza43
{
public static final String HIGH_SCORE_FILE = "coin-flip-score.txt";
public static void main( String[] args ) throws Exception
{
final Scanner keyboard = new Scanner(System.in);
final int highScore = getHighScore();
final int newScore = getScore(keyboard);
if(newScore != 0 && newScore > highScore){
final String name = getName(keyboard);
writeHighScore(name, newScore);
}
private static int highScore(){
// read high score from high score file or return Integer.MIN_VALUE if
// no high score file exists
}
private static int getScore(final Scanner keyboard){
// play game, prompt user, get input, etc. and then
// return the player's score.
}
private static String getName(final Scanner keyboard){
// prompt the user for their name and return their input
}
private static void writeHighScore(final String name, final int score){
// write this high score (with the name) to the high score file
}
}

How can I read numeric passwords in Java?

I am trying to get the user to enter a four digit pin but I don't want it to be printed out on the screen as they type it. I have tried using System.console().readPassword(); like so:
import java.util.Scanner;
import java.io.*;
import java.util.InputMismatchException;
public class VirtualATM{
private static String Details;
public static void main(String [] args){
try{
//Create variables & scanner to be used throughout the program.
Scanner sc = new Scanner(System.in);
boolean RegisterOrExist = false;
int cardNo = 0;
String DirToWriteFile = System.getProperty("user.dir") + "/VirtualATM.txt"; //Get path to write text file to.
DirToWriteFile.trim();
File file = new File(DirToWriteFile);
// if file doesn't exists, then create it
if (!file.exists()) {
file.createNewFile();
}
//Create writer to write to files.
FileWriter fw = new FileWriter(file.getAbsoluteFile());
BufferedWriter bw = new BufferedWriter(fw);
System.out.println("Enter card number, or type register to register a new card.");
String register = sc.nextLine();
if(register.equalsIgnoreCase("register")){
RegisterOrExist = false;
RegisterNewCard();
} else {
RegisterOrExist = true;
cardNo = Integer.valueOf(register);
}
bw.write(Details);
//Close the writer.
bw.close();
} catch(IOException e) {
e.printStackTrace();
}
}
/*** Method for registering a new card **/
public static void RegisterNewCard(){
Scanner sc = new Scanner(System.in);
System.out.print("Name: ");
String name = sc.nextLine();
int MaxVal = Integer.MAX_VALUE;
int CardNo = new java.util.Random().nextInt(MaxVal) + 1;
int balance = new java.util.Random().nextInt(10000) + 1;
boolean OverDraft = false;
int OverDraftLimit = 0;
if(OverDraft = true){
OverDraftLimit = 250;
}
char [] PIN = {};
System.out.println("Create a FOUR digit pin: ");
try{
PIN = System.console().readPassword();
}catch(InputMismatchException e){
e.printStackTrace();
}
int P1 = (int) PIN[0];
int P2 = (int) PIN[1];
int P3 = (int) PIN[2];
int P4 = (int) PIN[3];
int [] PinNo = {P1, P2, P3, P4};
Details = "Name: " + name + " CardNo: " + CardNo + " Current Balance: " + balance + " overdraft? " + OverDraft + " OverDraftLimit: " + OverDraftLimit + " pin: " + PinNo;
}
}
I then try to write the pin int [] pinNo = {P1, P2, P3, P4} to a text file using the BufferedWriter. I get the following this text in the text file when I input the pin as 2566:
[I#42a57993
Is there another way to read a password without it printing on the screen as the user types?

well this line
bw.write(Details);
is writing the details in the file where
Details = "..otherdetails..."+"pin: " + PinNo;
shows that you are writing the hash of the array. So simply replace "pin: " + PinNo with
the actual elements of the array
You can simply follow what Rod said or try this
Details = "..otherdetails..."+"pin: " + java.util.Arrays.toString(PinNo)
Tip - using this makes you password more secure
try like this
char[] PIN = System.console.readPassword();
Arrays.fill(password, ' ');

problem:
pin: " + PinNo;
You are actually printing the memory location of the array object not the array elements itself
solution:
you can get each index of the PinNo array and append each of them to the string
"pin: " + PinNo[0] + PinNo[1] + PinNo[2] + PinNo[3]

If you are trying to run your code on Eclipse IDE console then it'll not work. It is bug System.console() (Java 6.0) returns null when running inside Eclipse.
You need to run from command prompt or teminal, etc.
For more on this see these post :-
Hide input on command line - stackoverflow
Masking password input from the console - stackoverflow

How to find average mark of an array list that comes from a csv file (JAVA) [closed]

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I have a csv file that has a list with student id's, lastname, firstname, marks, phone number, etc. I have organized them into an array list so when you call stu[100].mark it will find the mark of the 100th student on the list of the csv file. There are 1000 students. I need to calculate the total overall average mark for all the students (each student only has one mark) I have put it in a loop, but it just prints out their mark. If you need more details, than I apologize.
Here is the code:
public class StudentRecs {
public static String user;
public int StuRec;
public static int numstu;
public static double average;
//public static StuRec[] stu;
static StuRec[] stu = new StuRec[1000];
public static void main(String[] args) throws IOException {
for (int i = 0; i < 1000; i++) {
stu[i] = new StuRec();
}
StuRec stu = new StuRec();
readFile(user);
menu();
}
public static String filename;
Scanner reader = new Scanner(filename);
public static Boolean readFile(String filename) throws IOException { //Constructor for filename
try {
Scanner userInput = new Scanner(System.in);
System.out.println("Type R To Read a File or Type Default for the default file");
user = userInput.nextLine();
if (user.equalsIgnoreCase("r")) {
user = userInput.nextLine();
}
filename = user;
if (user.equalsIgnoreCase("default")) {
filename = "newreg2.csv";
}
Scanner input = new Scanner(new FileReader(filename));
while (input.hasNext()) {
in(input.nextLine());
numstu++;
}
input.close();
return true;
} catch (IOException e) {
System.err.println(e.getMessage());
}
return false;
}
public static void in(String reader) {
String splitter[];
splitter = reader.split(",");
stu[numstu] = new StuRec();
stu[numstu].studentID = splitter[0];
stu[numstu].lastName = splitter[1];
stu[numstu].firstName = splitter[2];
stu[numstu].phoneNumber = splitter[3];
stu[numstu].courseCode = splitter[4];
stu[numstu].periodNumber = Integer.parseInt(splitter[5]); // parseInt turns a string of digits into an integer
stu[numstu].mark = Integer.parseInt(splitter[6]);
}
public static boolean menu() {
int total = 0;
String choice;
Scanner userInput = new Scanner(System.in);
System.out.println("=============================================");
System.out.println("Type R To Read Another File");
System.out.println("Type L To Print all File Records");
System.out.println("Type AA To Print The Average Of All The Marks");
choice = userInput.nextLine();
for (int i = 0; i < numstu; i++) {
if (choice.equalsIgnoreCase("L")) {
System.out.println(stu[i].lastName + ", " + stu[i].firstName + ", " + stu[i].studentID + ", " + stu[i].phoneNumber + ", " + stu[i].courseCode + ", " + stu[i].periodNumber + ", " + stu[i].mark);
}else if (choice.equalsIgnoreCase("R")){
} else if (choice.equalsIgnoreCase("AA")) {
total = total + stu[i].mark;
} else {
System.err.println("Unknown Key Try Again...");
}
average = total / 1000; // compute the average.
System.out.println(average);
} return menu();
}
}

Your average routine is computing incorrectly. It's simply taking the n'th mark and adding it to itself, divided by 1000. Since you're using integers, it will just round down, effectively giving you n'th mark + 0 for average on each iteration, leaving you with the last mark on the loop completion.
You need to keep adding to average, and divide by 1000 when you are done to get the value.
public static boolean menu() {
String choice;
Scanner userInput = new Scanner(System.in);
System.out.println("=============================================");
System.out.println("Type R To Read Another File");
System.out.println("Type L To Print all File Records");
System.out.println("Type AA To Print The Average Of All The Marks");
choice = userInput.nextLine();
for (int i = 0; i < numstu; i++) {
if (choice.equalsIgnoreCase("L")) {
System.out.println(stu[i].lastName + ", " + stu[i].firstName + ", " + stu[i].studentID + ", " + stu[i].phoneNumber + ", " + stu[i].courseCode + ", " + stu[i].periodNumber + ", " + stu[i].mark);
}else if (choice.equalsIgnoreCase("R")){
} else if (choice.equalsIgnoreCase("AA")) {
average += stu[i].mark; // keep adding to average
} else {
System.err.println("Unknown Key Try Again...");
}
}
// divide by zero protection
if ( numstu > 0 ) {
average = average/numstu; // compute the average. Always use the size in terms of a variable whenever possible.
System.out.println(average); // as noted below, if this is an integer value, < #of students computations will eval to 0.
// might be better to use double
}
else {
System.out.println("Oops! No students! :(");
}
return menu();
}
Note that your menu is a little inefficient, but the problem at hand should be solved.

Others have already pointed out the issue with not correctly calculating the sum of the scores, the numerator of the average calculation. I want to focus on the issue of the number of scores, the denominator of the average calculation.
Think real world. As others have mentioned, you cannot depend on the number of students in the file being fixed. File/class size can vary, so you cannot divide by a fixed number.
But neither can you depend on the number of scores being the same as the number of students, so you cannot simply divide by the number of students in that file. A student might not have a mark for a particular assignment (sickness, excused absence, or whatever). A good routine will account for the possibility of blanks (as well as invalid values), and thus I would expect you to need to count the valid, non-blank marks at the same time that you total them so that you can take the appropriate quotient at the end.

This statement is the problem
average = stu[i].mark + stu[i].mark / 1000;
This does not accumulate a total. Instead try
total = total + stu[i].mark;
And then at the end, outside the loop
average = total / 1000;