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How can I create a "high score list" on a txt file which stores top 10 scores and names of the players who scored them?

I need to make high score list in a txt file. In the first game, the txt file should be empty as it is the first game. After the first game, the score list must be updated each time with the player's name and the player's score. The list should of course be ordered from high to low according to player's score. After 10 games, the last ones should be removed and only 10 should remain in the list.
I am trying to do this but every time my txt file is stays empty. How can I fix this issue?
My HighScore class:
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;
import java.util.Formatter;
import java.nio.file.Paths;
public class HighScore {
public class HighScoreEntry {
private String name;
private int score;
public HighScoreEntry(String name, int score) {
this.name = name;
this.score = score;
}
public String getName() {
return name;
}
public int getScore() {
return score;
}
}
public void writeHighScores(HighScoreEntry[] highScores) {
Formatter f = null;
FileWriter fw = null;
try {
fw = new FileWriter("highscores.txt",true);
f = new Formatter(fw);
for (int i = 0; i < highScores.length; i++) {
f.format("%s:%d%n", highScores[i].getName(), highScores[i].getScore());
}
} catch (IOException e) {
System.out.println("An error occurred while writing the high scores file.");
} finally {
if (f != null) {
f.close();
}
}
}
public HighScoreEntry[] readHighScores() {
HighScoreEntry[] highScores = new HighScoreEntry[10];
// Initialize the high scores array with default values
for (int i = 0; i < highScores.length; i++) {
highScores[i] = new HighScoreEntry("", 0);
}
Scanner reader = null;
try {
reader = new Scanner(Paths.get("highscores.txt"));
int i = 0;
while (reader.hasNextLine() && i < 10) {
String line = reader.nextLine();
String[] parts = line.split(":");
String name = parts[0];
int score = Integer.parseInt(parts[1]);
highScores[i] = new HighScoreEntry(name, score);
i++;
}
} catch (IOException e) {
System.out.println("An error occurred while reading the high scores file.");
} finally {
if (reader != null) {
reader.close();
}
}
return highScores;
}
public void updateHighScores(String name, int score) {
System.out.println("Updating high scores with name " + name + " and score " + score);
// Write the player's score and name to the high scores file
writeHighScores(new HighScoreEntry[] {new HighScoreEntry(name, score)});
// Read the high scores from the file
HighScoreEntry[] highScores = readHighScores();
// Sort the high scores
sortHighScores(highScores);
}
private void sortHighScores(HighScoreEntry[] highScores) {
for (int i = 0; i < highScores.length - 1; i++) {
for (int j = i + 1; j < highScores.length; j++) {
if (highScores[i].getScore() < highScores[j].getScore()) {
HighScoreEntry temp = highScores[i];
highScores[i] = highScores[j];
highScores[j] = temp;
}
}
}
}
}
My calling method in Game class:
HighScore highScore = new HighScore();
highScore.updateHighScores(user, playerPoints);
I just have to use them. I can't use anything other than these.

The Formatter class returns a formatted string, but you're not capturing the return value of your format call, nor are you writing the resulting string to your FileWriter.
It should look something like this:
String result = f.format("%s:%d%n", highScores[i].getName(), highScores[i].getScore());
fw.write(string);
Give or take a newline.

how to select players join the game and start a game

I am a beginner in Java, and I've been creating a practicing project for a game. For this purpose, I've already put some features in this project, and I separate the entire project into three files: Nimsys, NimPlayer, NimGame.
I've created these features.
addplayer into playerList in the NimPlayer.
removeplayer
editplayer
Now, I want two of the players to join the game, and do the following:
Score record
The times the player has played.
What I did was trying to store the user data (addplayer) from the prompt input, and brought the game to be played (last part of the incomplete code).
import java.util.Scanner;
public class Nimsys {
public static String[] splitName(String inName) {
String[] splittedLine = inName.split(",");
String[] name = null;
if (splittedLine.length==3) {
String userName = splittedLine[0].trim();
String familyName = splittedLine[1].trim();
String givenName = splittedLine[2].trim();
name = new String[3];
name[0] = userName;
name[1] = familyName;
name[2] = givenName;
}
return name;
}
public static String [] splitData(String dataIn) {
String[] splittedLine = dataIn.split(",");
String[] data = null;
if (splittedLine.length==4) {
String initialStone = splittedLine[0];
String stoneRemoval = splittedLine[1];
String player1 = splittedLine[2].trim();
String player2 = splittedLine[3].trim();
data = new String[4];
data[0] = initialStone;
data[1] = stoneRemoval;
data[2] = player1;
data[3] = player2;
}
return data;
}
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
while (true) {
System.out.print('$');
String commandin = in.next();
if (commandin.equals("addplayer")) {
String inName = in.nextLine();
String[] name = splitName(inName);
//Make sure the vadality of in name
if (name!=null && name.length==3) {
for (int i = 0; i < NimPlayer.getId(); i ++) {
String userCheck = NimPlayer.getPlayer()[i].getUserName();
if (userCheck.contains(name[0])) {
System.out.println("The player already exist");//Test if player has been created
}
}
NimPlayer.createPlayer(name[0], name[1], name[2]);
System.out.println("The player has been created.");
} else {
System.out.println("Not Valid! Please enter again!");
}
}
if (commandin.equals("removeplayer")) {
//cannot loop through the entire null array, would be NullPointerException
String removeUserName = in.nextLine().trim();
/*System.out.println("Are you sure you want to remove all players? (y/n) \n");
//System.out.print('$');
commandin = in.next();
if (commandin.equals("y")) {
for (int i = 0; i < NimPlayer.getId(); i++) {
NimPlayer.getPlayer()[i] = null;
System.out.println("Remove all the players");
}
} else {
System.out.print('$');
}*/
//commandin = in.next();
for (int i = 0; i < NimPlayer.getId(); i++) {
String userName = NimPlayer.getPlayer()[i].getUserName().trim();
if (removeUserName != null && userName.equals(removeUserName)) {
NimPlayer.getPlayer()[i] = null;
System.out.println("Remove successfully!");// A test to see if the code runs
} else {
System.out.println("The player does not exist");
}
}
}
if (commandin.equals("editplayer")) {
String inName = in.nextLine();
String[] splittedLine = inName.split(",");
if (splittedLine!=null && splittedLine.length==3) {
String userName = splittedLine[0].trim();
String familyName = splittedLine[1].trim();
String givenName = splittedLine[2].trim();
//System.out.println(userName+","+familyName+","+givenName);//Test if in name in the if loop
for (int i = 0; i < NimPlayer.getId(); i++) {
String userCheck = NimPlayer.getPlayer()[i].getUserName().trim();
if (userName != null && userCheck.equals(userName)) {
NimPlayer.getPlayer()[i].setFamilyName(familyName);
NimPlayer.getPlayer()[i].setGivenName(givenName);
System.out.println("Edit successfully");
} else {
System.out.println("The player does not exist.");
}
}
} else {
System.out.println("Invalid in! Please enter again.");
}
}
if (commandin.equals("displayplayer")) {
for (int i = 0; i < NimPlayer.getId(); i++) {
String userName = NimPlayer.getPlayer()[i].getUserName();
String familyName = NimPlayer.getPlayer()[i].getfamilyName();
String givenName = NimPlayer.getPlayer()[i].getGivenName();
System.out.println(userName+","+familyName+""+givenName);
}
}
if (commandin.equals("startgame")) {
String dataIn = in.nextLine();
String [] data = splitData(dataIn);
//Check if player in the array
if (data.length==4 && data !=null) {
for (int i = 0; i < NimPlayer.getId(); i++) {
for (int j = i + 1; j < NimPlayer.getId(); j++) {
String player1 = NimPlayer.getPlayer()[i].getUserName();
String player2 = NimPlayer.getPlayer()[j].getUserName();
if (player1==null || player2==null) {
System.out.println("One of the players does not exist. Please enter again");
} else {
System.out.println("Data built successfully.Game starts!");
break;
}
}
}
dataIn = in.nextLine();
}
int dataStone = Integer.parseInt(data[0]);
int dataRemoval = Integer.parseInt(data[1]);
}
}}
//username, given name, family name, number of game played, number of games won
public class NimPlayer {
private String userName;
private String familyName;
private String givenName;
static NimPlayer[] playerList = new NimPlayer[10]; // set an array here
static int id;
//define NimPlayer data type
public NimPlayer(String userName,String surName, String givenName) {
this.userName = userName;
this.familyName = surName;
this.givenName = givenName;
}
// create new data using NimPlayer data type
public static void createPlayer(String userName, String familyName, String givenName) {
if (id<10) {
playerList[id++] = new NimPlayer(userName, familyName, givenName);
} else {
System.out.println("Cannot add more players.");
}
}
public static int getId() {
return id;
}
public static NimPlayer [] getPlayer() {
return playerList;
}
public void setUserName(String userName) {
this.userName = userName;
}
public void setFamilyName(String familyName) {
this.familyName = familyName;
}
public void setGivenName(String givenName) {
this.givenName = givenName;
}
public String getUserName() {
return userName;
}
public String getfamilyName() {
return familyName;
}
public String getGivenName() {
return givenName;
}
}
Above are my Nimsys and NimPlayers class. So far, I have a question:
Is it wrong to manipulate the players in the Nimplayer?
Or it is better to create an object in Nimsys if I want to store the record and the times game played?
public class NimGame {
int stoneBalance;
int stars;
public int initializeStone(int startStones) {
stoneBalance = startStones;
return stoneBalance;
}
public void removeStones(int stonesTaken) {
int updatedBalance = stoneBalance - stonesTaken;
stoneBalance = updatedBalance;
}
public void printStar(int star) {
stars = star;
stars = stoneBalance;
for (int stars = 1; stars <= star; stars++) {
System.out.print(" *");
}
System.out.println();
}
Scanner in = new Scanner(System.in);
String playOrNot;
do {
System.out.println("Initial stone count: "+datastone);
System.out.println("Maximum stone removal: "+dataRemoval);
System.out.println("Player 1: "+player1.getUserName());
System.out.println("Player 2: "+player2.getUserName());
// while stoneBalance > 0, two players keep playing the game
while (stoneBalance > 0) {
System.out.print(initialStone + " stones left:");
printStar(initialStone);
// player1's turn and remove the stones; decision of winning
System.out.println(player1 + "'s turn - remove how many?\n");
int takeStone = in.nextInt();
while (takeStone > dataRemoval || takeStone <= 0) {
System.out.println(
"Invalid, you need to remove stones under upper "+
"bound limit or above 0. \n Please enter again.");
takeStone = in.nextInt();
}
removeStones(takeStone); //remove the stone
if (stoneBalance > 0) {
//show the remaining stones
System.out.print(stoneBalance + " stones left:");
printStar(stoneBalance);
} else if (stoneBalance <= 0) {
System.out.println("Game Over\n" + player2 + " wins!\n");
break;
}
// player2's turn and remove the stones; decision of winning
System.out.println(player2 + "'s turn - remove how many?\n");
takeStone = in.nextInt();
while (takeStone > dataRemoval || takeStone <= 0) {
System.out.println(
"Invalid, you need to remove stones under upper " +
"bound limit or above 0. \n Please enter again.");
takeStone = in.nextInt();
}
removeStones(takeStone);
if (stoneBalance > 0) {
System.out.print(stoneBalance + " stones left:");
printStar(stoneBalance);
} else if (stoneBalance <= 0) {
System.out.println("Game Over\n" + player1 + " wins!\n");
break;
}
}
// ask players to play again
in.nextLine();
System.out.println("Do you want to play again (Y/N):");
playOrNot = in.nextLine();
} while (playOrNot.equals("Y"));
}
And this above is my NimGame class. It's the process of the classical Nim game. What should I do to introduce the player? What I did in Nimsys is only to check if players are inside the playerList.
Thanks for taking the time to review my code. Any help is highly appreciated!

On a side note (because it won't affect the execution of the program), the name of an identifier should be self-explanatory e.g. your getPlayer method should be named as getPlayerList as it is returning the playerList, not a single player.
Your logic for startgame should be as follows:
if (commandin.equals("startgame")) {
String dataIn = null, player1 = null, player2 = null;
do {
dataIn = in.nextLine();
String [] data = splitData(dataIn);
//Check if player in the array
if (data !=null && data.length==4) {
NimPlayer[] players = NimPlayer.getPlayerList();
for (int i = 0; i < players.length; i++) {
if(players[i].getUserName().equals(data[2])) {// Checking player1
player1 = players[i].getUserName();
break;
}
}
for (int i = 0; i < players.length; i++) {
if(players[i].getUserName().equals(data[3])) {// Checking player2
player2 = players[i].getUserName();
break;
}
}
}
} while(player1 == null || player2 == null)
//...
}
You can put the repeated code in a function to make your program modular e.g.
String findPlayerByName(String name){
String player = null;
NimPlayer[] players = NimPlayer.getPlayerList();
for (int i = 0; i < players.length; i++) {
if(players[i].getUserName().equals(name)) {
player = players[i].getUserName();
break;
}
}
return player;
}
Then, the logic for startgame will reduce to:
if (commandin.equals("startgame")) {
String dataIn = null, player1 = null, player2 = null;
do {
dataIn = in.nextLine();
String [] data = splitData(dataIn);
//Check if player in the array
if (data !=null && data.length==4) {
player1 = findPlayerByName(data[2]);
player2 = findPlayerByName(data[3]);
}
} while(player1 == null || player2 == null)
//...
}
Another thing I would like you to understand is the problem with the following line:
if (data.length==4 && data !=null)
It should be
if (data !=null && data.length==4)
This way, if data is null, the condition, data.length==4 will not be checked because && operator allows to proceed further only if the condition on its left side evaluates to true.
The problem with your line is that if data is null, you will get the NullPointerException because you will be checking .length on a null reference.
Now, I want two of the players to join the game, and do the following:
Score record
The times the player has played.
Currently, you have userName, familyName, and givenName attributes in NimPlayer class. You need to create two more attributes, private int score and private int numbersOfGamesPlayed with their public getters and setters. You need to use these attributes to store the value of score and the numbers of time a player has played the game.

ArrayIndexOutOfBounds Exception Error When Displaying Reservations After Booking - Java

I'm making a reservation feature for my events, and I can successfully add the attendee, however when I want to display the details for every attendee, it gives me a ArrayIndexOutOfBounds exception error, which I'm not quite sure how to fix.
Main.java
private static Scanner sc = new Scanner(System.in);
private static int eventCreationLimit = 5;
private static Event[] events = new Event[eventCreationLimit];
private static int eventsCreated;
public static void main(String args[]) {
String input;
// Main menu.
do {
System.out.println("\n~ BOOKING SYSTEM ~");
System.out.println("------------------");
System.out.println("A. Schedule an Event");
System.out.println("B. Add an Attendee");
System.out.println("C. View Reservations");
System.out.println("X. Exit\n");
System.out.print("Select an option: ");
input = sc.nextLine();
switch (input.toUpperCase()) {
case "A":
scheduleAnEvent();
break;
case "B":
addAttendee();
break;
case "C":
displayReservations();
break;
case "X":
System.out.println("INFO: You have exited the booking system.");
break;
default:
System.out.println("ERROR: Invalid input!");
}
} while (!input.equalsIgnoreCase("X"));
}
private static void scheduleAnEvent() {
System.out.println("\n~ SCHEDULE A EVENT ~");
System.out.println("--------------------");
System.out.print("Enter the ID: ");
String ID = sc.nextLine();
...
System.out.print("Enter the attendee limit: ");
int attendeeLimit = Integer.parseInt(sc.nextLine());
// Add the new event to the array.
events[eventsCreated++] = new Event(ID, ..., attendeeLimit, attendeeLimit, ...);
for (int i = 0; i < eventsCreated; i++)
// Set the places available for the specific event being created to subtract it later when an attendee is added.
if (ID.equals(events[i].getID()))
// The number of places available left in the event can be displayed by going to "B. View All Events".
events[i].setPlacesAvailable(attendeeLimit);
// Give the user a confirmation message.
System.out.println("\nINFO: Sucessfully created Event: " + ID + ".");
}
private static void addAttendee() {
Event event = null;
boolean result = false;
System.out.println("\n~ ADD AN ATTENDEE ~");
System.out.println("-------------------");
System.out.print("Enter attendee name: ");
String name = sc.nextLine();
System.out.print("Enter attendee phone number: ");
String phone = sc.nextLine();
Attendee a = new Attendee(name, phone);
System.out.print("Enter event ID: ");
String eventID = sc.nextLine();
// Check if the given ID matches an event.
for (int i = 0; i < eventsCreated; i++)
if (events[i].getID().equals(eventID))
event = events[i];
if (event != null) {
if (event.getID().equals(eventID)) {
result = ((Event) event).addAttendee(a);
if (result) {
// If the event has enough room, then add the attendee.
System.out.println("INFO: Attendee successfully added to Event: " + eventID + ".");
displayReservations();
}
else
// If the event is full, then the attendee will not be added.
System.out.println("ERROR: The Event: " + eventID + " is full, the attendee could not be added.");
} else
System.out.println("ERROR: The given ID does not match any existing event.");
} else
System.out.println("ERROR: The event was not found.");
}
private static void displayReservations() {
System.out.println("\n~ RESERVATIONS ~");
System.out.println("----------------");
String pattern = "%-18s %-18s %-22s %-1s\n";
System.out.printf(pattern, "NAME", "PHONE", "EVENT ID", "FEE");
System.out.println("----------------------------------------------------------------");
// Display all reservations for events.
for (int i = 0; i < events[i].getAttendeeCount(); i++)
events[i].displayReservations();
}
Event.java
...
private String ID;
private int attendeeLimit;
private int attendeeCount;
private int placesAvailable;
private Attendee[] a = new Attendee[attendeeCount];
public Demonstration(..., String ID, int placesAvailable, int attendeeLimit, ...) {
this.ID = ID;
this.placesAvailable = placesAvailable;
this.attendeeLimit = attendeeLimit;
}
public String getID() { return this.ID; }
public int getPlacesAvailable() { return this.placesAvailable; }
public int getAttendeeLimit() { return this.attendeeLimit; }
public void setPlacesAvailable(int placesAvailable) { this.placesAvailable = placesAvailable; }
public boolean addAttendee(Attendee at) {
// Proceed to add the attendee if there is enough room.
if (attendeeCount <= placesAvailable) {
attendeeCount++;
// Decrease the number of places available by one.
setPlacesAvailable(placesAvailable - 1);
return true;
}
return false;
}
public void displayReservations() {
System.out.println("ID: " + ID);
if (attendeeCount > 0)
for (int i = 0; i < attendeeCount; i++)
a[i].attendeeDetails();
}
Attendee.java
private String name;
private String phone;
public Attendee(String name, String phone) {
this.name = name;
this.phone = phone;
}
public String getName() { return this.name; }
public String getPhone() { return this.phone; }
public void attendeeDetails() {
System.out.println("Name: " + name);
System.out.println("Phone: " + phone);
}
The above code gives me a ArrayIndexOutOfBoundsException error in the displayReservations() method (a[i].attendeeDetails()) whenever I try to add an attendee to an event.
Problem: How do I display all reservation details for all events? Thank you for your help!
EDIT
The error:
Index 0 out of bounds for length 0.

There are a couple of issues with your code:
You are maintaining an attendeeCount separately than the size of the Attendee[], but in your addAttendee() method, you never actually add the new Attendee to the array
Because Attendee[] is an array, it can't grow larger than the size when first initialized. If you want to use an array, instead of an ArrayList that can grow dynamically, you need to initialize the array to the maximum size: placesAvailable:
So, my recommendation would be to switch from using an array to an ArrayList by importing java.util.Arraylist, changing the declaration of the Attendee[] to an ArrayList, and updating the rest of the Event.java code to use the ArrayList, as well as making sure you add the new Attendee in the addAttendee() method. Finally, you don't need to maintain the attendee count separately, just ask the attendees ArrayList it's current size.
Event.java
...
import java.util.*; //You can import all java.util classes
private String ID;
private int attendeeLimit;
private int placesAvailable;
private List<Attendee> attendees = new ArrayList<>(); //Initialize the attendees ArrayList
public Demonstration(..., String ID, int placesAvailable, int attendeeLimit, ...) {
this.ID = ID;
this.placesAvailable = placesAvailable;
this.attendeeLimit = attendeeLimit;
}
public String getID() { return this.ID; }
public int getPlacesAvailable() { return this.placesAvailable; }
public int getAttendeeLimit() { return this.attendeeLimit; }
public void setPlacesAvailable(int placesAvailable) { this.placesAvailable = placesAvailable; }
public boolean addAttendee(Attendee at) {
// Proceed to add the attendee if there is enough room.
if (attendeeCount <= placesAvailable) {
attendees.add(at); //Make sure you add the new Attendee to the list
// Decrease the number of places available by one.
setPlacesAvailable(placesAvailable - 1);
return true;
}
return false;
}
public void displayReservations() {
System.out.println("ID: " + ID);
int attendeeCount = attendees.size(); //Calculate the number of Attendees
if (attendeeCount > 0)
for (int i = 0; i < attendeeCount; i++)
attendees.get(i).attendeeDetails();
}

attendeCount does not have a value as at the time you creating the Array "a". For what you are trying to achieve, I suggest:
i. Use an Arraylist.
ii. Initialize you array in the constructor to attendeLimit.
If possible, I also suggest you use parameter methods where neccessary.

Need help using an ArrayList

It seems that 20 regiments were in a continuous process of formation. The first had 1000 men, the second had 950, the third 900, and so on down to the twentieth regiment, which garrisoned only 50. During each week, 100 men were added to each regiment, and at week's end, the largest regiment was sent off to the front.This lasted for a total of 20 weeks.
For this program I have already managed to print out the original number of men for each regiment. But I am having difficult adding 100 men to each regiment.The adding men must be a method in the army class. I am getting the regiment objects using a .txt file. All this files contains is the names of regiments numbered 1-20.
I currently have no errors my only problem is that I do not know how to add men to my regiment. I have to use the addMen method in the army class which I currently have blank.
public class Regiment {
private String name; //name of regiment
private int regNumber; //regiment number
private int men; // regiment men
public Regiment(int regNumber, String name, int men) {
this.name = name;
this.regNumber = regNumber;
this.men = men;
}
public String getName() {
return name;
}
public int getregNumber() {
return regNumber;
}
public int getMen() {
return men;
}
public int addMen2(int RegNumber) {
int men = 1050 - (regNumber * 50);
return men;
}
}
ArmyDataList:
class ArmyDataList {
public ArrayList<Regiment> list;
public ArmyDataList() {
list = new ArrayList<Regiment>();
}
public void AddToList(Regiment current) {
list.add(current);
}
public void RemoveFromList(Regiment current) {
list.remove(current);
}
public Regiment getLargest() {
if (list.isEmpty()) {
return null;
}
Regiment Reg1 = list.get(0);
for (int i = 1; i < list.size(); i++) {
Regiment current = list.get(i); // get next regiment
// is current regiment > largest
if (current.getMen() > Reg1.getMen()) {
Reg1 = current;
}
}
return Reg1;
}
public void addMen() {
}
public String toString() {
String out
= String.format("%28s%12s%n", "Regiments", " Men")
+ String.format("%12s%n", "Number")
+ String.format("%12s%16s%14s%n", "=======", "===============",
"=========");
for (int i = 0; i < list.size(); i++) {
Regiment regim = list.get(i);
int regNumber = regim.getregNumber();
String name = regim.getName();
int men = regim.addMen2(regNumber);
out = out + String.format("%12s", regNumber)
+ String.format("%16s", name)
+ String.format("%10s", men)
+ "\n";
}
return out + "\n";
}
}
RegimentTest:
public class RegimentTest {
public static void main(String[] args) throws IOException
{
ArmyDataList army = new ArmyDataList();
Scanner fileScan = new Scanner(new File("regiments.txt"));
System.out.println("Report Summary:\n");
while (fileScan.hasNext()) {
String line = fileScan.nextLine();
System.out.println(line);
Scanner in = new Scanner(line) ;
int regNumber = in.nextInt();
String name = in.next();
int men = 0 ; //men is set to 0 only because I havent add the men yet
Regiment adder = new Regiment(regNumber, name, men );
army.AddToList(adder) ;
}
System.out.println(army.toString());
}

Add a setMen(int numberOfMen) method to your Regiment class. Then in your addMen() method, you can do something like this:
public void addMen(){
for(Regiment r : list){ //iterate through the list of regiments
r.setMen(r.getMen() + 100); //add 100 men to each regiment
}
}
The setMen method would look like this:
public void setMen(int numberOfMen){
men = numberOfMen;
}
There is another issue with your toString method, where the regiment's addMen2 method is called - right now you're just printing the number, not initializing the number of men. In the constructor for your Regiment class, replace the line
this.men = men;
with
this.men = addMen2(regNumber);
Then in your toString method, replace
int men = regim.addMen2(regNumber);
with
int men = regim.getMen();
Here is what your main should look like:
public static void main(String[] args) throws IOException{
ArmyDataList army = new ArmyDataList();
Scanner fileScan = new Scanner(new File("regiments.txt"));
System.out.println("Report Summary:\n");
while (fileScan.hasNext()) {
String line = fileScan.nextLine();
System.out.println(line);
Scanner in = new Scanner(line);
int regNumber = in.nextInt();
String name = in.next();
int men = 0 ; //men is set to 0 only because I havent add the men yet
Regiment adder = new Regiment(regNumber, name, men );
army.AddToList(adder);
}
System.out.println(army.toString()); //print out the initial # of men
for(int i = 0; i < 20; i++)
army.addMen();
System.out.println(army.toString()); //print the final # of men
}

in Regiment get rid of method addMen2, and replace it with
public void addMen(int men) {
this.men +=men;
}
then in your army you could have method
public void addMen(int men) {
for(Regiment regiment : list){
regiment.addMen(men);
}
}
that will be simplest solution to add 100 men to each regiment,
other thing is, your toString is bit nasty, regiment should know how meny soldiers it ghas, you shouldnt need additional method to calculate it (reason why i recommend you to trash addMen2 method)
to initiate your Regiment, use constructor. You want to have regiments in sizes 1000, 1950, 1900 etc, do it when you are creating them
while (fileScan.hasNext()) {
String line = fileScan.nextLine();
System.out.println(line);
Scanner in = new Scanner(line) ;
int regNumber = in.nextInt();
String name = in.next();
int men = 1050 - (regNumber * 50);
Regiment adder = new Regiment(regNumber, name, men );
army.AddToList(adder) ;
}

Cannot read text file into array and write to text file again

This my whole code.
I want to make a simple program that will read a
text file and put it to array then write it to the
same text file,
also can add and delete the existing input and my input.
Problem
The delete and writer part seems not working, only blank text file when I run the code
These are the error after I select the exit.
java.lang.NullPointerException at ContactList.writer(ContactList.java:51) at
ContactListDriver.main(ContactListDriver.java:73) at
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at
sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at
sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at
java.lang.reflect.Method.invoke(Unknown Source) at
edu.rice.cs.drjava.model.compiler.JavacCompiler.runCommand(JavacCompiler.java:27‌​2)
public class Contact {
//Each contact stores the name, phone number, and email address
private String name;
private String number;
private String email;
public Contact(String name, String number, String email)
{
this.name = name;
this.number = number;
this.email = email;
}
public String getName()
{
return name;
}
public String getNumber()
{
return number;
}
public String getEmail()
{
return email;
}
public void setName(String name)
{
this.name = name;
}
public void setNumber(String number)
{
this.number = number;
}
public void setEmail(String email)
{
this.email = email;
}
}
class for processing the inputs.
import java.io.*;
import java.lang.*;
import java.util.*;
public class ContactList {
public Contact[] myContacts;
public static final int MAX = 100;
private int numContacts;
public ContactList()
{
myContacts = new Contact[MAX];
numContacts = 0;
}
public void addContact(String name, String number, String email)
{
Contact c = new Contact(name, number, email);
myContacts[numContacts] = c;
numContacts++;
}
public void deleteContact(String name)
{
for ( int i = 0; i <= numContacts-1 ; i++){
if( name == myContacts[i].getName())
{
myContacts[i] = null;
break;
}
}
numContacts--;
}
public void writer(){
String x = "MyContacts.txt";
try {
PrintWriter outputs = new PrintWriter(x);
for( int i=0; i < myContacts.length; i++)
{
Contact c = myContacts[i];
if(c!=null){ // check if c is null before writing to file
outputs.println(""+c.getName()+" "+c.getNumber()+" "+c.getName());
outputs.flush();
}
}
outputs.close();
}catch (IOException e) {
e.printStackTrace();
}
catch(NullPointerException ex){
}
}
public void displayContacts()
{
int i;
for(i=0; i < myContacts.length; i++)
{
Contact c = myContacts[i];
if(null != c){
System.out.println("Name: " + c.getName());
System.out.println("Number: " + c.getNumber());
System.out.println("Email: " + c.getEmail());
System.out.println("------------------------------------");
}
}
}
}
/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
The Driver....
public class ContactListDriver {
public static void main(String[] args) throws FileNotFoundException
{
ContactList cList = new ContactList();
File in = new File("MyContacts.txt");
Scanner sc = new Scanner(in);
int option;
char again = 'n';
String name = null;
String number = null;
String email = null;
while(sc.hasNext())
{
//read one line from text file
String entry = sc.nextLine();
//System.out.println(entry);
String[] con = entry.split("\\s+");
//System.out.println(con[0] + " " + con[1] + " " + con[2]);
cList.addContact(con[0], con[1], con[2]);
}
Scanner userIn = new Scanner(System.in);
do{
displayOptions();
option = userIn.nextInt();
switch(option)
{
case 1:
System.out.println(" Name > ");
name = userIn.next();
System.out.println(" Number > ");
number = userIn.next();
System.out.println(" Email Address > ");
email = userIn.next();
cList.addContact(name, number, email);
break;
case 2:
//delete contact
System.out.println("Contact Name > ");
name = userIn.next();
cList.deleteContact(name);
break;
case 3:
//display contact
cList.displayContacts();
break;
case 4:
cList.writer();
System.out.println(" are you sure ? press y ");
String x = userIn.next();
again = x.charAt(0);
break;
}
}while( again == 'n' );
}
private static void displayOptions() {
System.out.println("(1) Add");
System.out.println("(2) Delete");
System.out.println("(3) Show Contacts");
System.out.println("(4) Exit");
}
}

One problem I see is:
You have a extra break; statement inside deleteContact(String name) function
and String comparision name == myContacts[i].getName() should be name.equals(myContacts[i].getName())
public void deleteContact(String name)
{
for ( int i = 0; i <= numContacts-1; i++){
if( name.equals( myContacts[i].getName()))// string comparison uses equals();
{
myContacts[i] = null;
numContacts--; // this line should be inside of if condition
break;
}
// break; No need of breaking the loop here
}
}
Another problem is at writer() function
public void writer(){
String x = "MyContacts.txt";
try {
PrintWriter outputs = new PrintWriter(x);
for( int i=0; i < myContacts.length; i++)
{
Contact c = myContacts[i];
if(c!=null){ // check if c is null before writing to file
outputs.println(""+c.getName()+" "+c.getNumber()+" "+c.getName());
outputs.flush();
}
}
outputs.close();
}catch (IOException e) {
e.printStackTrace();
}
catch(NullPointerException ex){ // Or just catch the NPE
}

You have declared and initialized the Contact array of size MAX. but,it seems to be that you haven't initialized the elements though. i.e. c is null in the below code
Contact c = myContacts[i];
outputs.println(""+c.getName()+" "+c.getNumber()+" "+c.getName());
outputs.flush();
myContacts[i] should return a Contact instance. As said by Meno, there are lot of other problems in your code. You have to always cover all the possible scenarios while writing the code.

Most importantly you need to fix the ContactList class. It is inserting new elements into the last index, and deleting at any location using the name.
For example, let's say the ContactList has three elements in it at 0, 1 and 2 indexes. So numContacts is set to 3.
Now ContactList has elements as:
[0]C0, [1]C1, [2]C2, [3]null, ...
Then if the contact at 0 index is deleted (set to null), then numContacts is set to 2.
Now the ContactList has elements as:
[0]null, [1]C1, [2]C2, [3] null, ...
A new insert will be added to the index 2, and it will override the C2 value.
Simplest solution is to use an ArrayList instead of an array.
As others have mentioned there are few more issues to fix, but above is the most important in my opinion.

There are many issues with your code so not easy to say where to begin.
First: Your public void deleteContact(String name)-method is broken. It compares Strings using == instead of equals(). And worse: It creates null pointers mid in your array which will cause problems in your writer()-method.
Second: Why do you use arrays? You should use java.util.ArrayList which offers out-of-the-box implementations for adding, getting and deleting contacts.
Third: If you are missing your text file, you might have overlooked it because of missing path so you don't know where to look for this file. So please add a full path to file name.
Fourth: I would also use scanner.hasNextLine() instead of scanner.hasNext() if you then call scanner.nextLine().
Since you said you are not allowed to use ArrayList you should study its source code especially for removing elements. It does not only nullify the array bucket, but also to shift all following elements one index backwards so you don't have any null gap until the index given by element count. And two breaks in deleteContact()-method are really not necessary.