Develop Reference

Why does my method overwrite positions in my array

So I have this method here
while(oMenu == 1 || oMenu == 2){
oMeny = Kbd.readInt("\nClick 1 to make an account\nClick 2 to login\nClick 3 to exit the program");
if(oMeny == 1){
for(int i = 0; Account[i] != null; i++){
if(Account[i] == null){
pos = i;
}
}
Account[pos] = new Account();
}
if(oMeny == 2){
String s = Kbd.readString("Input your accountnumber: ");
for(int i = 0; Account[i] != null; i++){
if(Account[i] != null && s.equals(Account[i].getAccountNumber())){
System.out.println("Welcome!");
// Here is rest of my code , the "inner" menu that works menyMetod(iMeny,mMeny);
}
else{
System.out.println("There are no accounts with that given accountnumber!");
}
}
}
}
}
I want to understand why if I access the oMeny == 1 and make 2 accounts Why I can't seem to access the first one I make but rather the latest one? It seems that somehow my array "overwrites" the first empty position. Basically I want to find the first empty position in my array, so in the first case it's always index 0 and then the next time I make an account again, it should be Index 1 logically.
EDIT : Heres my code for the Account class
public class Account{
private int money, transactions;
private String AccountNumber;
public Account(){
money = Kbd.readInt("\nHow much money do you want to put in?");
AccountNumber = Kbd.readString("\nWhat account number do you want?");
}

The error is here:
for (int i = 0; accounts[i] != null; i++) {
if (accounts[i] == null)
The for loop repeats as long i points to a non-null entry. Therefore the if-condition is never true.
This becomes quickly obvious when you run the program line by line in a debugger.
Next time please provide a complete code example that can be compiled. Your code is full of error, It took me a lot of time to fix it before I was able to execute it.
Corrected code:
import java.util.Scanner;
class Main
{
static Scanner kbd = new Scanner(System.in);
static Account[] accounts = new Account[100];
static class Account
{
//public int money;
public String accountNumber;
public Account()
{
//System.out.println("\nHow much money do you want to put in?");
//money = Kbd.nextInt();
System.out.println("\nWhat account number do you want?");
accountNumber = kbd.next();
}
}
public static void main(String[] args)
{
int oMenu = 1;
int pos = 0;
while (oMenu == 1 || oMenu == 2)
{
System.out.println("\nClick 1 to make an account\nClick 2 to login\nClick 3 to exit the program");
oMenu = kbd.nextInt();
if (oMenu == 1)
{
for (int i = 0; i<accounts.length; i++)
{
if (accounts[i] == null)
{
accounts[i] = new Account();
break;
}
}
}
if (oMenu == 2)
{
System.out.println("Input your accountnumber: ");
String s = kbd.next();
Account found=null;
for (int i = 0; i<accounts.length; i++)
{
if (accounts[i] != null && s.equals(accounts[i].accountNumber))
{
found=accounts[i];
}
}
if (found!=null)
{
System.out.println("Welcome! nr. "+found.accountNumber);
}
else
{
System.out.println("There are no accounts with that given accountnumber!");
}
}
}
}
}
Notice how I also fixed the second for-loop.

You did not show the declaration or initialization of pos, so I think it is not working how you expect because you do not go into the for loop where Account[i] is null to set pos. Try this
if(oMenu == 1){
int pos = 0;
while (Account[pos] != null && pos < Account.length)
pos++;
if (pos < Account.length)
Account[pos] = new Account();
else{
//expand array and add account or throw error
}
}

Validating user input in arrays

Hey guys I am doing a project for school and am having a little trouble, I have a variable "reservationNumber" and im attempting to check if the number the user inputs is in the array, if not it returns a string saying the number was not found. It is working fine and displays the correct info when there is a valid input but when an invalid input is detected it gives a null.pointer.exception error. I tried writing it so that if the number is not detected the private method returns -1, then when I call the tickerInformation method, if that the variable 'ticket' returns -1 then it returns "invalid reservation number". This is where is error is being raised and only occurs when I enter an invalid number please help.
public void ticketInformation(String reservationNumber)
{
int ticket = searchArray(reservationNumber);
if (ticket == -1)
{
System.out.println("The reservation number entered was n0t found");
}
else
{
System.out.print("\n" + ticketSale[ticket].toString());
}
}
private int searchArray(String reservationNumber)
{
for (int i = 0; i < ticketSale.length; i++)
{
if (ticketSale[i].getReservationNumber().equals(reservationNumber))
{
return i;
}
}
return -1;
}

ticketSale[i].getReservationNumber().equals(reservationNumber) has an issue. Share the declaration and init for array "ticketSale". If ticketSale array is for abstract data type then why equal is called with String?

You didn't post the whole code but I think that when you enter invalid number as reservation number, it does not assigned to the related object's instance variable. So getReservationNumber() might be returning null.

Add a null check,
private int searchTicketSales(String reservationNumber) {
int reservationNumberIndex = -1;
for (int i = 0; i < ticketSale.length; i++) {
if (null != ticketSale[i].getReservationNumber() && ticketSale[i].getReservationNumber().equals(reservationNumber)) {
reservationNumberIndex = i;
break;
}
}
return reservationNumberIndex;
}
Best Regards,
Rakesh

Add a regex to validate that your input is a valid number "\\d+":
public void ticketInformation(String reservationNumber)
{
String regex = "\\d+";
if(!reservationNumber.matches(regex))
{
System.out.println("The reservation number entered was n0t found");
}
int ticket = searchArray(reservationNumber);
if(ticket == -1)
{
System.out.println("The reservation number entered was n0t found");
}
else
{
System.out.print("\n" + ticketSale[ticket].toString());
}
}
You might want to validate searchArray, particularly if it is not used interdependently from ticketInformation().

specifying the path for input data and output data

I am new in java and I have to use the code below but the code it does work because I have to specifying the path for input data and output data. The code is got it from the internet. please help me
class Svm_scale
{
private BufferedReader rewind(BufferedReader fp, String filename) throws IOException
{
fp.close();
return new BufferedReader(new FileReader(filename));
}
private void output_target(double value)
{
LnCount++;
if(y_scaling)
{
if(value == y_min)
value = y_lower;
else if(value == y_max)
value = y_upper;
else
value = y_lower + (y_upper-y_lower) *
(value-y_min) / (y_max-y_min);
}
formatterscaled.format(value+" ");
System.out.println(" Line Number "+LnCount + " ");
}
private void output(int index, double value)
{
count++;
double Threshold1=0,Threshold2=0;
Threshold1= Avg[index]+(STDV[index]/2);
Threshold2= Avg[index]-(STDV[index]/2);
if(value > Threshold1 )
value = 2;
else if(value < Threshold2 )
value = -2;
else
value = 0;
formatterscaled.format( formatter.format(value) + ",");
// System.out.println(" Counter "+count);
// }
}

String save_filename =Save1; // = null?
String restore_filename =null;
String scale_data_filename =Disc; // set this to the path where the output should be stored, e.g. = "C:\\temp\\scaled";
String data_filename =Libsvm; // set this to the path where the input can be get, e.g. = "C:\\temp\\inputdata"
These are the Strings you need to adapt in order that the program can read and write. Save1, Disc, Libsvm are not in your code, so it can only be guessed where they come from.
data_filename and scale_data_filename are required. save_filename seems to be optional and may be set to null.

Finding duplicates in an array of objects

The purpose of this project is to make a pokedex that adds and holds all the pokemon passed in by user input. When the user inputs a pokemon that is already stored in the pokedex the word "duplicate" is supposed to be printed to the console. The word duplicate is printed even though there are no actual duplicates within the object array. Here is my output from the console :
Welcome to your new PokeDex!
How many Pokemon are in your region?: 3
Your new Pokedex can hold 3 Pokemon. Let's start using it!
List Pokemon
Add Pokemon
Check a Pokemon's Stats
Sort Pokemon
Exit
What would you like to do? 2
Please enter the Pokemon's Species: red
Duplicate
Now here is all the code used that could possibly be making this error
import java.util.Scanner;
public class Project4 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.println("Welcome to your new PokeDex!");
System.out.print("How many Pokemon are in your region?: ");
int size = input.nextInt();
Pokedex pokedex = new Pokedex(size);
System.out.println("\nYour new Pokedex can hold " + size + " Pokemon. Let's start using it!");
int choice = 0;
boolean done = false;
while (!done) {
System.out.println("\n1. List Pokemon\n2. Add Pokemon\n3. Check a Pokemon's Stats" + "\n4. Sort Pokemon\n5. Exit");
System.out.print("\nWhat would you like to do? ");
choice = input.nextInt();
switch (choice) {
case 1:
String[] pokemonList = pokedex.listPokemon();
if (pokemonList == null)
System.out.println("Empty");
else
for (int i = 0; i < pokemonList.length; i++) {
System.out.println((i + 1) + ". " + pokemonList[i]);
}
break;
case 2:
System.out.print("\nPlease enter the Pokemon's Species: ");
String species = input.next();
pokedex.addPokemon(species);
break;
}
}
}
}
In the following class I have the actual method that adds the pokemon and the constructor for Pokedex
public class Pokedex {
Pokemon[] pokedex;
String pokeArray[];
public Pokedex(int size) {
pokedex = new Pokemon[size];
pokeArray = new String[size];
}
public boolean addPokemon(String species) {
Pokemon stuff = new Pokemon(species);
for (int i = 0; i < pokedex.length; i++) {
if (pokedex[i] == null) {
pokedex[i] = stuff;
}
else if (i < pokedex.length && pokedex[i] != null) {
System.out.println("Max");
}
if (pokedex[i].getSpecies().equalsIgnoreCase(species)) {
System.out.print("Duplicate");
break;
}
}
return false;
}
}
Sorry for the mass amounts of code I just need help tracing where this unexpected result is coming from.

The reason it's doing that is because of this bit of code here:
public boolean addPokemon(String species)
{
Pokemon stuff = new Pokemon(species);
for (int i = 0; i < pokedex.length; i++)
{
if (pokedex[i] == null)
pokedex[i] = stuff;
else if (i < pokedex.length && pokedex[i] !=null)
System.out.println("Max");
if(pokedex[i].getSpecies().equalsIgnoreCase(species))
{
System.out.print("Duplicate");
break;
}
}
return false;
}
The problem is just a little bit of syntax missing. In your for loop, you check to see if
A) there are any empty spots in the array
B) if every element in the array up to the user inputted size is full
and C) if any element in the array matches the one we're trying to add.
The problem you're encountering is because your C is an if instead of an else if. Because A sees the index is null, it assigns the new Pokemon to the Pokedex. Then because C is an if instead of an else if, it runs after you assign the new Pokemon and sees the Pokemon we just added and says it's a duplicate. Changing it to an else if would fix this.
Also, since there was no break; in A, it would assign every element of the array to the first one entered, causing any further additions to call Max. I edited the code and this is what I had that worked for me:
public boolean addPokemon(String species)
{
Pokemon stuff = new Pokemon(species);
for (int i = 0; i < pokedex.length; i++)
{
if(pokedex[i] !=null && pokedex[i].getSpecies().equalsIgnoreCase(species))
{
System.out.println("Duplicate");
break;
}
else if (pokedex[i] == null)
{
pokedex[i] = stuff;
break;
}
else if(i + 1 == pokedex.length)
{
System.out.println("Max");
break;
}
}
return false;
}
Also, out of curiosity, why is the addPokemon() function a boolean? You return a value (albeit arbitrarily) and then never do anything with that value. You could just make it a void, have it return nothing, and it would work just as fine.

Exception organization assistance?

I had some success with this site, and I hope I find more excellent programmers to assist me.
So I am at my wit's end with this code. I am very new to programming, especially exceptions. I have looked very hard through my course material and sought help, but I have been quite unsuccessful. I am trying to create an improved parser that will override another parser. It reads a .txt file with student information of it including an ID, a name, a grade, and an optional email address and optional comment as tokens in a String separated by commas. The override checks for errors in each token and throws an exception called ParserException. The exception will check the code and then return an error message if the error is unfixable.
For example, if a student puts in an AB for the grade, the exception will flag and check if the input is a valid grade (which it is) and then return, if it is not, then it will throw a ParserException, in this case
throw new ParserException(ParserException.GRADE_INVALID_GRADE,lineIndex);
This shows that the does not work and sends out a message GRADE_INVALID on the line indexLine
I have a list of what I need to have as an output:
Any violation of the file format specified in the Input File Format Description section above should result in an ParcerException with an appropriate message
Duplicate IDs are not allowed
Grade values must be a float (92.0) or a letter grade and not an integer
I have all the code to correct and check for errors, but I cannot figure out how to get the try-catch to work. Here's is the override code:
#Override
public ParserResult parseLine(int lineIndex) {
String[] tokens = lines.get(lineIndex).split(",");
ArrayList<Integer> idList = new ArrayList<Integer>();
Integer studentId;
String name;
String grade;
String email;
String comments;
boolean isFloat;
float gradeFinal;
String editName;
studentId = new Integer(tokens[0]);
ParserResult result;
try{
return super.parseLine(lineIndex);
}
catch(ParserException e){
// Check reasonable number of tokens
if(tokens.length >= 3 && tokens.length <= 5){
name = tokens[1];
grade = tokens[2];
// Check the student ID
if(idList.contains(studentId)){
throw new ParserException(ParserException.DUPLICATE_ID, lineIndex);
}else{
idList.add(studentId);
}
// Check the grade
if(grade.trim().equalsIgnoreCase("A")){
gradeFinal = gradeA;
}else if(grade.trim().equalsIgnoreCase("AB")){
gradeFinal = gradeAB;
}else if(grade.trim().equalsIgnoreCase("B")){
gradeFinal = gradeB;
}else if(grade.trim().equalsIgnoreCase("BC")){
gradeFinal = gradeBC;
}else if(grade.trim().equalsIgnoreCase("C")){
gradeFinal = gradeC;
}else if(grade.trim().equalsIgnoreCase("CD")){
gradeFinal = gradeCD;
}else if(grade.trim().equalsIgnoreCase("D")){
gradeFinal = gradeD;
}else if(grade.trim().equalsIgnoreCase("F")){
gradeFinal = gradeF;
}else{
try{
Integer.parseInt(grade);
isFloat = false;
}
catch(Exception fl) {
isFloat = true;
}
if(isFloat){
if((Float.parseFloat(grade) < 100f) && (Float.parseFloat(grade) >= 0f)){
gradeFinal = Float.parseFloat(grade);
}else{
throw new ParserException(ParserException.GRADE_INVALID_GRADE,lineIndex);
}
}else{
throw new ParserException(ParserException.GRADE_INTEGER_VALUE,lineIndex);
}
}
// Check the name
if(name.split(" ").length > 3){
throw new ParserException(ParserException.UNKNOWN, lineIndex);
}else{
editName = name.trim().split(" ")[0];
}
result = new ParserResult(studentId, editName, gradeFinal);
// Checks the email
if(tokens.length >= 4){
email = tokens[3];
// Check for at sign
if(!email.contains("#")){
throw new ParserException(ParserException.UNKNOWN, lineIndex);
}
int count = 0;
// Counts number of # symbols
for(int i=0; i<email.length(); i++){
if(email.indexOf(i) == '#'){
count++;
}
}
if(count > 1){
throw new ParserException(ParserException.EMAIL_MULTIPLE_AT,lineIndex);
}
if(email.split(".").length == 2){
if(!(email.trim().split(".")[1].contains(".edu")) && !(email.trim().split(".")[1].contains(".com"))){
throw new ParserException(ParserException.EMAIL_NOT_EDU_OR_COM,lineIndex);
}else{
result.setEmail(email);
}
}
// Checks if email contains .com or .edu
// Checks the comments
if(tokens.length == 5){
comments = tokens[4];
result.setComment(comments);
}
}
return result;
}
}
// TODO Call Parser's parseLine() here to attempt to parse, catch any exceptions
return null;
}
The original parseLine that is overridden, but still used is:
public ParserResult parseLine(int lineIndex) {
String[] tokens = lines.get(lineIndex).split(",");
ParserResult result = new ParserResult(Integer.parseInt(tokens[0]),
tokens[1], Float.parseFloat(tokens[2]));
result.setEmail(tokens[3]);
return result;
}
Here is the main() file:
public static void main(String[] args){
// TODO Change the line below to use ImprovedParser
Parser parser = null;
try {
parser = new ImprovedParser(args[0]);
} catch (FileNotFoundException e) {
e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.
System.exit(-1);
}
List<ParserResult> results = parser.parse();
int count = results.size();
double sum = 0.0;
for (ParserResult result : results) {
sum += result.getGrade();
}
System.out.println("Number of valid input lines: " + results.size());
System.out.println("Number of invalid input lines: "
+ (parser.getLineCount() - results.size()));
System.out.println("Average grade: " + sum / count);
for (ParserResult result : results) {
System.out.println(result);
}
}
Lastly, here is the .txt file that is being read:
# student_id,name,grade,email
1234,Bob,92.0,bob#test.edu
4321,Alice,95.0,alice#test.edu
1111,Eve,80.0,eve#test.edu
1121,Barry,85.0,barrytest.edu
1131,Harry,86.0,h#rry#test.edu
1121,Larry,87.0,larry#test.edu
1141,Jim Song,88.0,jim#song.edu
1151,Jerry,77.0,jerry#test.net
1161,James,65.0,james#test.com
The last six inputs should cause exceptions, but I can't figure out how to organize it to work. The code ignores the line with # symbol.
Here is a sample successful output:
Number of valid input lines: 3
Number of invalid input lines: 0
Average grade: 89.0
1234, 92.0, Bob, bob#test.edu,
4321, 95.0, Alice, alice#test.edu,
1111, 80.0, Eve, eve#test.edu,
The major changes should be in the orverride method
Please help if you can, I sit at my desk still pondering possibilities, and your help will be most-appreciated.

Assuming ParseException has an error field being an int and someMethod() that throws ParseException:
try {
someMethod();
} catch (final ParseExeption ex) {
if (ex.getError() == ParseException.SOME_ERROR) {
// do something
} else if (ex.getError() == ParseException.OTHER_ERROR) {
// do something else
}
}
Note that it's usually better to use specific exceptions for specific error, something like SomeErrorParseException, OtherErrorParseException, ... (those can extends ParseException if you want) and try-catch like this:
try {
someMethod();
} catch (final SomeErrorParseException ex) {
// do something
} catch (final OtherErrorParseException ex) {
// do something else
}
Some reading: http://docs.oracle.com/javase/tutorial/essential/exceptions/index.html

It seems that there is no code to actually cause the catch clause in the first place. Try adding a throw new ParserException(STUFF_HERE); when an error has been detected while reading the file.