Develop Reference

Java parsing multiple files

I need to parse multiple files and get access to the object's methods outside of where they were initialized.
This is my code:
public static void main(String[] args) {
try {
File Attrationfile = new File("attractions.txt");
Scanner attractionscanner = null;
attractionscanner = new Scanner(Attrationfile);
while (attractionscanner.hasNext()) {
String nextline = attractionscanner.nextLine();
String[] Attractioncomponents = nextline.split("#");
String ridename =Attractioncomponents[0];
int price = Integer.parseInt(Attractioncomponents[1]);
String type = Attractioncomponents[2];
int unknown = Integer.parseInt(Attractioncomponents[3]) ;
double speed = Attractioncomponents.length <= 4 ? 0 :
Double.parseDouble(Attractioncomponents[4]);
RollerCoaster rollerCoaster = new RollerCoaster(ridename, price , unknown, speed);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}
try {
File Customerfile = new File("customers.txt");
Scanner Customerscanner = new Scanner(Customerfile);
while (Customerscanner.hasNext()) {
String nextline = Customerscanner.nextLine();
String[] Customercomponents = nextline.split("#");
int accountnumber =Integer.parseInt(Customercomponents[0]);
String name = Customercomponents[1];
int age = Integer.parseInt(Customercomponents[2]) ;
int balance = Integer.parseInt(Customercomponents[3]) ;
String discount = Customercomponents.length <= 4
? String.valueOf(0) : Customercomponents[4];
Customer customer= new Customer(accountnumber,name, age, balance, discount);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
This works but I can't get access to the objects outside of their loops. I am not sure how the Сustomer class would get information about the roller coaster, such as the name and price. For example, if the customer and rollercoaster objects were in the same area, I would be able to update the customer balance by taking away rollercoaster.getprice from the customer.getbalance, and setting customer.setbalance to the value of the calculation. As you have probably already gathered, I am a beginner, so I am probably going about this in the wrong way - thanks.

You can change the scope for those variables by declaring them at the start of the main method.
public static void main(String[] args) {
Customer customer = null;
RollerCoaster rollerCoaster = null;
try {
File Attrationfile = new File("attractions.txt");
Scanner attractionscanner = null;
attractionscanner = new Scanner(Attrationfile);
while (attractionscanner.hasNext()) {
String nextline = attractionscanner.nextLine();
String[] Attractioncomponents = nextline.split("#");
String ridename =Attractioncomponents[0];
int price = Integer.parseInt(Attractioncomponents[1]);
String type = Attractioncomponents[2];
int unknown = Integer.parseInt(Attractioncomponents[3]) ;
double speed = Attractioncomponents.length <= 4 ? 0 :
Double.parseDouble(Attractioncomponents[4]);
rollerCoaster = new RollerCoaster(ridename, price , unknown, speed);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}
try {
File Customerfile = new File("customers.txt");
Scanner Customerscanner = new Scanner(Customerfile);
while (Customerscanner.hasNext()) {
String nextline = Customerscanner.nextLine();
String[] Customercomponents = nextline.split("#");
int accountnumber =Integer.parseInt(Customercomponents[0]);
String name = Customercomponents[1];
int age = Integer.parseInt(Customercomponents[2]) ;
int balance = Integer.parseInt(Customercomponents[3]) ;
String discount = Customercomponents.length <= 4 ? String.valueOf(0) :
Customercomponents[4];
customer= new Customer(accountnumber,name , age , balance, discount);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}

Welcome to SO! As Hovercraft pointed out, the objects are declared within the scope of the loop, meaning you can't access them outside of it as you noticed. Also, they are overwritten on every iteration, since you declare and initialize the object on every pass. Consider using an ArrayList like so (here just for the customers):
ArrayList<Customer> customerList = new ArrayList<>();
try {
while (customerScanner.hasNext()) {
// ...
customerList.add(new Customer(accountnumber,name, age, balance, discount));
}
} catch (...) {
// ...
}
Here's the doc for the ArrayList. <T> is a generic type, which for you means that you can have an ArrayList<Customer>, ArrayList<RollerCoaster>, ArrayList<String> ...
Sidenote: By convention, variable names start with a lowercase letter, like Scanner customerScanner instead of Scanner Customerscanner.

Is it a question of scope? Try to declare an object outside the body of the loop.
Because in Java, the brace is a scope. The more nested braces, the smaller the scope. You can try to declare the objects you need to call in the external scope in the same or larger scope
String type = null;
RollerCoaster rollerCoaster = null;
while (attractionscanner.hasNext()) {
String nextline = attractionscanner.nextLine();
String[] Attractioncomponents = nextline.split("#");
String ridename =Attractioncomponents[0];
int price = Integer.parseInt(Attractioncomponents[1]);
type = Attractioncomponents[2];
int unknown = Integer.parseInt(Attractioncomponents[3]) ;
double speed = Attractioncomponents.length <= 4 ? 0 :
Double.parseDouble(Attractioncomponents[4]);
rollerCoaster = new RollerCoaster(ridename, price , unknown, speed);
}

LinkedList of File IO appears the same through output

The LinkedList only shows the same output. I am trying to use the last while loop but it does not work. This is a "Duck Duck Goose" problem. I am not supposed to use Indexing.
19 names
http://collabedit.com/q248e
public class DuckDuckGoose {
public static void main(String[] args) {
LinkedList<String> linkedlist = new LinkedList<String>();
// add try catch to add list
try {
FileReader fr = new FileReader(...players.txt");
Scanner inFile = new Scanner(fr);
while (inFile.hasNextLine()) {
linkedlist.add(inFile.nextLine());
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}
Iterator<String> iterator = linkedlist.iterator();
// checks until the last list
while (!iterator.hasNext()) {
if (iterator.next().equals(getRandomBoolean())) {
iterator.remove();
}
}
System.out.println(linkedlist);
}
public static boolean getRandomBoolean() {
return Math.random() < 10 * 0.5;
}
}

if (iterator.next().equals(getRandomBoolean())) {
This is never true, because the iterator contains Strings, not Booleans, so you never execute the iterator.remove();.
Instead:
iterator.next(); // gets but ignores the next String.
if (getRandomBoolean()) {
Additionally, your loop never executes:
while (!iterator.hasNext()) {
because the iterator initially has a next element.
Remove the !.
Additionally, this:
Math.random() < 10 * 0.5
Is always true, because Math.random() is strictly less than 1, and 10 * 0.5 is 5.
Drop the 10 *, or pick a value on the RHS of the < which is between 0 and 1.

Alternate for multiple try catch to handle the exception

I am trying to read a CSV file with 20 columns which may or may not contain value but the problem is that I have to create 20 try catch in order to maintain the code flow in control manner. Like
String a = ""; loop
try{
a = list.get(0); // converted the csv to list of list and iterated in
}catch(NoSuchElementException e){}
and same for every other variable.The reason I have seperate try catch because In the below code
String a = "";
String b = "";
try{
a = list.get(0);
b = list.get(1);
}catch(NoSuchElementException e){}
If first line of try gave exception the second line will not execute.
So is there any alternate to these n number of try catch situation?
Thanks

You could create a helper method:
private String getField(List<String> list, int n) {
try {
return list.get(n);
} catch (NoSuchElementException e) {
return "";
}
}
String a = getField(list, 0);
String b = getField(list, 1);
EDIT:
Typically you wouldn't rely on exceptions if you do not have sufficient fields, the following achieves the same thing but subjectively feels cleaner:
private String getField(List<String> list, int n) {
if (n < list.size()) {
return list.get(n);
}
return "";
}

Saving Objects from an Iterated List

I'm currently workin' on a sales module using java+hibernate+oracle... I'm done with my order form in my jsp like this:
I'm getting my parameters doing this:
ArrayList<String> idMercaderias = new ArrayList<String>();
ArrayList<String> cantidades = new ArrayList<String>();
ArrayList<String> precios = new ArrayList<String>();
for (int k = 0; k < 10; k++) {
idMercaderias.add(request.getParameter("idMercaderia" + k));
cantidades.add(request.getParameter("cantidad" + k));
precios.add(request.getParameter("precio" + k));
}
I have 10 rows on my order detail, so I made the for, where my inputs are input1, input2, input3, etc. These are attributes of my object Mercaderia so i need to set them up, since they're on lists:
First I'm filtering the first list to avoid repeated articles:
Iterator itra = idMercaderias.listIterator();
ArrayList<String> sortedListIdMercaderias = new ArrayList<String>();
Object m;
while (itra.hasNext()) {
m = itra.next();
if (!sortedListIdMercaderias.contains(m)) {
sortedListIdMercaderias.add((String) m);
}
}
Now I create my object to set all the attributes:
DetallePedido detalle = new DetallePedido();
Now I'm doing a cycle 10 times (thinking of all rows in my form) and start to iterate each list to get my object attributes avoiding null or empty entries.
for (int x = 0; x < sortedListIdMercaderias.size(); x++) {
Iterator itr = idMercaderias.listIterator();
while (itr.hasNext()) {
String mercaderia = (String) itr.next();
if ((mercaderia != null) && (!mercaderia.equals(""))) {
Mercaderia mercaderiaSeleccionada = new MercaderiaDAO().findById(Integer.parseInt(mercaderia));
detalle.setMercaderia(mercaderiaSeleccionada);
}
}
Iterator itr2 = cantidades.listIterator();
while (itr2.hasNext()) {
String cantidad = (String) itr2.next();
if ((cantidad != null) && (!cantidad.equals(""))) {
int cantidadMercaderiaSeleccionada = Integer.parseInt(cantidad);
detalle.setCantidad(cantidadMercaderiaSeleccionada);
}
}
Iterator itr3 = precios.listIterator();
while (itr3.hasNext()) {
String precio = (String) itr3.next();
if ((precio != null) && (!precio.equals(""))) {
BigDecimal precioMercaderiaSeleccionada = new BigDecimal(precio);
detalle.setPrecioUnitario(precioMercaderiaSeleccionada);
}
}
Finally i just persist to my database:
Session session = new DetallePedidoDAO().getSession();
Transaction tx = session.beginTransaction();
try {
session.saveOrUpdate(detalle);
tx.commit();
session.close();
} catch (HibernateException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
I don't know why in the database i only get 1 row inserted (the last one with valid data) instead of all of them.
Any help will be really apreciated, this is for my final test in university project.

You've only ever got one DetallePedido object. You're changing its field values over and over in the various loops, but it's still just one object. Lastly you're saving it. Just once. Naturally, you only get one row inserted in your database.
What you could try is, instead of iterating through your Mercaderia objects, your Cantidad objects and your Precio objects separately; have a single loop that WITHIN EACH ITERATION creates a new DetallePedido object, sets the Mercaderia, the Cantidada and the Precio, and then saves the DetallePedido.

So, following the clues by David Wallace I made some tweaks to the idea and created an object WrapperDetallePedido like this:
public class WrapperDetallePedido {
int idMercaderia;
int cantidad;
double precio;
public int getIdMercaderia() {
return idMercaderia;
}
public void setIdMercaderia(int idMercaderia) {
this.idMercaderia = idMercaderia;
}
public int getCantidad() {
return cantidad;
}
public void setCantidad(int cantidad) {
this.cantidad = cantidad;
}
public double getPrecio() {
return precio;
}
public void setPrecio(double precio) {
this.precio = precio;
}
}
Then in my Controller I created a single ArrayList and set my DetallePedido attributes:
ArrayList<WrapperDetallePedido> listado = new ArrayList<WrapperDetallePedido>();
for (int k = 0; k < 10; k++) {
if (!request.getParameter("idMercaderia" + k).equals("")){
WrapperDetallePedido WDetallePedido = new WrapperDetallePedido();
WDetallePedido.setIdMercaderia(Integer.parseInt(request.getParameter("idMercaderia" + k)));
WDetallePedido.setCantidad(Integer.parseInt(request.getParameter("cantidad" + k)));
WDetallePedido.setPrecio(Double.parseDouble(request.getParameter("precio" + k)));
listado.add(WDetallePedido);
}
}
Finally used Iterator for the previous list and set all the items from listado and persist to the database:
for (Iterator iterador = listado.listIterator(); iterador.hasNext();) {
WrapperDetallePedido detalle = (WrapperDetallePedido) iterador.next();
Mercaderia mercaderiaSeleccionada = new MercaderiaDAO().findById(detalle.getIdMercaderia());
DetallePedido detallePedido = new DetallePedido();
detallePedido.setMercaderia(mercaderiaSeleccionada);
detallePedido.setCantidad(detalle.getCantidad());
detallePedido.setPrecioUnitario(new BigDecimal(detalle.getPrecio()));
detallePedido.setPedidos(pedidoGenerado);
Session session1 = new DetallePedidoDAO().getSession();
Transaction tx1 = session1.beginTransaction();
new DetallePedidoDAO().save(detallePedido);
try {
session1.saveOrUpdate(detallePedido);
tx1.commit();
session1.close();
} catch (HibernateException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
Finally got all my rows inserted as i needed... Thank you!

Calling Two Different Methods into One Method in Java

I wish to:
Reading in two files
Split the files into individual strings
Compare the two string lists and retrieve strings that are unique to a file.
At the moment I am running in to the problem of finding a way to call the two methods used to call in the files (one for each file) to the same method in order to be compared.
Both methods use a try-catch-while statement and if I try to read all of the entries after the while statement only a single is shown and not the entire list.
Is there a way to send parts of both methods as parameter to a single new method?
Here is the code for the program. I know that there are problems with the way that I am doing the program, but I am only doing it the way that I was taught.
File mainEmails = new File("Testrun.txt");
Scanner inputScanner = null;
int counter = 1;
String fullName = null;
String position = null;
String companyName = null;
String telNumber = null;
String emailAddress = null;
try
{
inputScanner = new Scanner(mainEmails);
}
catch(FileNotFoundException e)
{
System.out.println("File has not been found.");
}
while (inputScanner.hasNextLine())
{
String nextLine = inputScanner.nextLine();
String [] splitFile = nextLine.split(",");
for (int i = 0; i <splitFile.length;i++)
{
if(i==0)
{
fullName = splitFile[0];
}
else if(i==1)
{
position = splitFile[1];
}
else if(i==2)
{
companyName = splitFile[2];
}
else if(i==3)
{
telNumber = splitFile[3];
}
else if(i==4)
{
emailAddress = splitFile[4];
}
else if(splitFile[i] == null)
{
System.out.println("You have failed!");
}
}
}
public static void deletionList()
{
File deletionEmails = new File("Testrun1.txt");
Scanner inputScanner1 = null;
String deletionfullName = null;
String deletionposition = null;
String deletioncompanyName= null;
String deletiontelNumber = null;
String deletionemailAddress = null;
try
{
inputScanner1 = new Scanner(deletionEmails);
}
catch(FileNotFoundException e)
{
System.out.println("File has not been found.");
}
while (inputScanner1.hasNextLine())
{
String deletionnextLine = inputScanner1.nextLine();
String [] deletionsplitFile = deletionnextLine.split(",");
for (int i = 0; i <deletionsplitFile.length;i++)
{
if(i==0)
{
deletionfullName = deletionsplitFile[0];
}
else if(i==1)
{
deletionposition = deletionsplitFile[1];
}
else if(i==2)
{
deletioncompanyName = deletionsplitFile[2];
}
else if(i==3)
{
deletiontelNumber = deletionsplitFile[3];
}
else if(i==4)
{
deletionemailAddress = deletionsplitFile[4];
}
else if(deletionsplitFile[i] == null)
{
System.out.println("You have failed!");
}
}
}
}
What I am trying to do is to take the fullName, emailAddress from the first split and deletionfullName and deletionemailAddress from the second split and compare the first and second of each, respectively. Each file will have a number of fields in it, and I am only interested in the fullName and emailAddress fields.

It is quite confusing to understand how you are trying to implement your solution, so may I suggest you look at a different way of doing the whole read-and-compare process. For example, I would suggest doing something like this... (in psuedocode)
public void compareFiles(String file1, String file2){
// Read the lines of each file into String[] arrays
String[] file1Lines = readAndSplitIntoLines(file1);
String[] file2Lines = readAndSplitIntoLines(file2);
// compare the lines
for (int x=0;x<file1Lines.length;x++){
for (int y=0;y<file2Lines.length;y++){
if (file1Lines[x].equals(file2Lines[y])){
// match. set it to null
file1Lines[x] = null;
file2Lines[y] = null;
// break out of the inner loop and start comparing the next line
break;
}
}
// remove the duplicates (which are now null values), creating a smaller array of uniques.
String[] newFile1 = shrinkArrayByRemovingNulls(file1Lines);
String[] newFile2 = shrinkArrayByRemovingNulls(file2Lines);
}

Besides the fact that your question is not very clear, you have at least one glaring problem:
DO NOT use exception handling for logic! Exception handling should be only for exceptions.
Secondly, think about what you are really looking to do. In pseudocode it would look something like this:
list1 = split(file(name1).read())
list2 = split(file(name2).read())
list3 = unique(list1, list2)
What does your code look like?