Develop Reference

Adding console input to ArrayList in Java

I'm trying to add items from the console input and scanner input to arraylists in java.
(To run the program user types Program ID)
The problem is that each time I run the program the contents of the arraylists update to only what has been entered that time. I would like the arraylists to contain all of the inputs that have been entered.
public class User{
private static List<String> listNames = new ArrayList<String>();
private static List<Integer> listIds = new ArrayList<Integer>();
public static void main(String[] args)
{
int tempID = 5000;
if (args.length>0) tempID= Integer.parseInt(args[0]);
System.out.println("Login "+tempID);
Scanner scanner = new Scanner(System.in);
System.out.print("Enter your Name : ");
tempName = scanner.nextLine();
User n = new User();
n.ID= tempID;
n.name = tempName;
listIds.add(n.ID);
listNames.add(n.name);
}
}
}
Does anyone know if this is possible?

Everytime you run the program it is going to initialize a different array. To solve this, you can store your data in a database such as MySQL or Oracle. But a more efficient way to solve this is that to save your ArrayList as an object locally using java.io.ObjectInputStream and java.io.ObjectOutputStream
I wrote the following 2 functions
public static ArrayList<Object> loadArrayList(String filename)
{
ObjectInputStream ois = null;
try {
ois = new ObjectInputStream(new FileInputStream(filename));
ArrayList<Object> arr = (ArrayList<Object>) ois.readObject();
return arr;
} catch (IOException e) {
e.printStackTrace();
return null;
} catch (ClassNotFoundException e) {
e.printStackTrace();
return null;
} finally {
if (ois != null) {
try {
ois.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
public static void saveArrayList(ArrayList<Object> arr, String filename)
{
ObjectOutputStream oos = null;
try {
oos = new ObjectOutputStream(new FileOutputStream(filename));
oos.writeObject(arr);
} catch (IOException e) {
e.printStackTrace();
} finally {
if (oos != null) {
try {
oos.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
Call saveArrayList with the first argument is your ArrayList instance and the second argument the filename. You can then load from your local file system using the loadArrayList method with the argument is your filename.
In your case, just call the saveArrayList method when your user exits the program and call the loadArrayList to get all your elements from the previous inputs to resume the user's progress

Every time you compile your program you create new Arrays. So you need another way of saving your inputs like in a SQL Database or you can run your program infinitely with a loop and ask each time for a new entry and collect it with the scanner like you already did but with that method, you can do nothing with the array entries because your asking for entries never stops.

Any explanation as to why Output Stream only prints the last line of the translated variable to a new file instead of all the lines?

I am trying to convert English words from a text file to a new file that translates the words into pig Latin. Everything translates the way it should when it is simply printed to the console but the issue I am having is that only the last line from the initial file appears on the new one.
public static void newFile(String pigLatin) {
OutputStream os = null;
try {
os = new FileOutputStream(new File("/Users/amie/Documents/inputnewnew.pig.txt"));
os.write(pigLatin.getBytes(), 0, pigLatin.length());
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
os.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}

By default FileOutputStream is overriding the existing file. What you need to do is to use another constructor with append parameter
FileOutputStream(String name, boolean append)
like
os = new FileOutputStream(new File("/Users/...", true))
Take a look at the reference

Java-Write in file

I want get name, last name and a spacial code from user, and save in one array, after that write to a file. My code doesn't have compiler error but it doesn't work.
public class WriteFile {
public static void main(String[] args){
try {
String array[][] = new String[100][2];
for (int i = 0; i < array.length; i++) {
RandomAccessFile raf=new RandomAccessFile("D://employee.txt","rw");
String inputName=JOptionPane.showInputDialog("Please Insert First Name");
array[i][0]=inputName;
String inputLName=JOptionPane.showInputDialog("Please Insert Last Name");
array[i][1]=inputLName;
String inputMeliiC=JOptionPane.showInputDialog("Please Insert Melii Code");
array[i][2]=inputMeliiC;
raf.writeUTF(array[i][0]);
raf.writeUTF(array[i][1]) ;
raf.writeUTF(array[i][1]);
}
} catch (FileNotFoundException e) {
e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.
} catch (IOException e) {
e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.
}
}

You are doing many things wrong.
First of all, why do you use an array at all here? It is unwarranted. Collect in a List!
Second: .writeUTF() will not write text.
Third: why write as you ask for input? Write all at once.
Fourth: you don't close your resource at all.
Ask for input first, then attempt to write to the file. And don't use File, it's obsolete. Use this (supposes Java 7+):
final Path dst = Paths.get("d:\\employee.txt");
// Change open options if necessary
try (
final BufferedWriter writer = Files.newBufferedWriter(dst,
StandardCharsets.UTF_8,
StandardOpenOption.CREATE, StandardOpenOption.APPEND);
) {
// write your data
}
Or even better yet, use this. Provided you have collected all of your employee data in a List as I suggest, and not an array, this is as easy as:
Files.write(thePath, myList, StandardCharsets.UTF_8, yourOpenOptionsHere);

Ok well you can for this modified code:
public static void main(String[] args){
RandomAccessFile raf = null;
try {
String array[][] = new String[2][3];
raf=new RandomAccessFile("D:\\employee.txt","rw");
for (int i = 0; i < array.length; i++) {
String inputName=JOptionPane.showInputDialog("Please Insert First Name");
array[i][0]=inputName;
String inputLName=JOptionPane.showInputDialog("Please Insert Last Name");
array[i][1]=inputLName;
String inputMeliiC=JOptionPane.showInputDialog("Please Insert Melii Code");
array[i][2]=inputMeliiC;
raf.writeChars(array[i][0]);
raf.writeChar(':');
raf.writeChars(array[i][1]) ;
raf.writeChar(':');
raf.writeChars(array[i][2]);
raf.writeChars("\n");
}
raf.seek(0);
String str = raf.readLine();
while(str != null ){
System.out.println(str);
String arr[] = str.split(":");
System.out.println(Arrays.asList(arr));
str = raf.readLine();
}
raf.close();
} catch (FileNotFoundException e) {
try {
raf.close();
} catch (IOException ex) {
Logger.getLogger(Ideone.class.getName()).log(Level.SEVERE, null, ex);
}
e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.
} catch (IOException e) {
try {
raf.close();
} catch (IOException ex) {
Logger.getLogger(Ideone.class.getName()).log(Level.SEVERE, null, ex);
}
e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.
}
}

Couple of issues:
You defined array as new String[100][2] and using it till the index array[i][2]=inputMeliiC; As array starts from 0, you should define your array as new String[100][3]. Are you doing further processing on your array?
You are not writing the inputMeliiC, instead you are duplicating the inputLName bu doing raf.writeUTF(array[i][1]); twice. You should do raf.writeUTF(array[i][2]);
Most importantly why you r write is not working is, you need to flush out the buffer. So you should do raf.close(); once you are done. Make sure UTF wont write in simple text as you are entering and you are opening file in both read write mode.

reading variables buried in java exception handling

I am writing a function to take a text file and count how many lines it has while outputting the lines to an array of strings. Doing this I have several exceptions I need to look out for. The class function has several variables that should have a scope throughout the function but when I write a value to the function inside of an exception, the return statement cannot find it. I've moved the declaration around and nothing helps
The value returned "h5Files" "Might not have been initialized" Since I don't know how long the array will be I cannot initialize it to a certain length. I do this within the code and I need a way to tell the return statement that I now have a values
Here is the code
public String[] ReadScanlist(String fileIn){
int i;
String directory ="c:\\data\\"; // "\" is an illegal character
System.out.println(directory);
int linereader = 0;
String h5Files[];
File fileToRead = new File(directory + fileIn);
System.out.println(fileToRead);
try {
FileInputStream fin = new FileInputStream(fileToRead); // open this file
}
catch(FileNotFoundException exc) {
System.out.println("File Not Found");
}
try{
//read bytes until EOF is detected
do {
FileReader fr = new FileReader(fileToRead);// Need to convert to reader
LineNumberReader lineToRead = new LineNumberReader(fr); // Use line number reader class
//
while (lineToRead.readLine() != null){
linereader++;
}
linereader = 0;
lineToRead.setLineNumber(0); //reset line number
h5Files = new String[linereader];
while (lineToRead.readLine() != null){
h5Files[linereader] = lineToRead.readLine(); // deposit string into array
linereader++;
}
return h5Files;
}
while(i !=-1); // When i = -1 the end of the file has been reached
}
catch(IOException exc) {
System.out.println("Error reading file.");
}
try{
FileInputStream fin = new FileInputStream(fileToRead);
fin.close(); // close the file
}
catch(IOException exc) {
System.out.println("Error Closing File");
}
return h5Files;
}

Your code is very very odd. For example these two blocks make no sense:
try {
FileInputStream fin = new FileInputStream(fileToRead); // open this file
}
catch(FileNotFoundException exc) {
System.out.println("File Not Found");
}
try{
FileInputStream fin = new FileInputStream(fileToRead);
fin.close(); // close the file
}
catch(IOException exc) {
System.out.println("Error Closing File");
}
I don't know what you think they do, but besides the first one leaking memory, they do nothing at all. The comments are more worrying, they suggest that you need to do more reading on IO in Java.
Deleting those blocks and tidying the code a (moving declarations, formatting) gives this:
public String[] ReadScanlist(String fileIn) {
String directory = "c:\\data\\";
String h5Files[];
File fileToRead = new File(directory + fileIn);
try {
int i = 0;
do {
FileReader fr = new FileReader(fileToRead);
LineNumberReader lineToRead = new LineNumberReader(fr);
int linereader = 0;
while (lineToRead.readLine() != null) {
linereader++;
}
linereader = 0;
lineToRead.setLineNumber(0);
h5Files = new String[linereader];
while (lineToRead.readLine() != null) {
h5Files[linereader] = lineToRead.readLine();
linereader++;
}
return h5Files;
} while (i != -1);
} catch (IOException exc) {
System.out.println("Error reading file.");
}
return h5Files;
}
My first bone of contention is the File related code. First, File abstracts from the underlying OS, so using / is absolutely fine. Second, there is a reason File has a File, String constructor, this code should read:
File directory = new File("c:/data");
File fileToRead = new File(directory, fileIn);
But it should really be using the new Path API anyway (see below).
So, you declare h5Files[]. You then proceed to read the whole file to count the lines. You then assign h5Files[] to an array of the correct size. Finally you fill the array.
If you have an error anywhere before you assign h5Files[] you have not initialised it and therefore cannot return it. This is what the compiler is telling you.
I don't know what i does in this code, it is assigned to 0 at the top and then never reassigned. This is an infinite loop.
So, you need to rethink your logic. I would recommend throwing an IOException if you cannot read the file. Never return null - this is an anti-pattern and leads to all those thousands of null checks in your code. If you never return null you will never have to check for it.
May I suggest the following alternative code:
If you are on Java 7:
public String[] ReadScanlist(String fileIn) throws IOException {
final Path root = Paths.get("C:/data");
final List<String> lines = Files.readAllLines(root.resolve(fileIn), StandardCharsets.UTF_8);
return lines.toArray(new String[lines.size()]);
}
Or, if you have Java 8:
public String[] ReadScanlist(String fileIn) throws IOException {
final Path root = Paths.get("C:/data");
try (final Stream<String> lines = Files.lines(root.resolve(fileIn), StandardCharsets.UTF_8)) {
return lines.toArray(String[]::new);
}
}

Since I don't know how long the array will be I cannot initialize it
to a certain length.
I don't think an array is the correct solution for you then - not to say it can't be done, but you would be re-inventing the wheel.
I would suggest you use a LinkedList instead, something like:
LinkedList<String> h5Files = new LinkedList<>();
h5Files.add(lineToRead.readLine());
Alternatively you could re-invent the wheel by setting the array to an arbritary value, say 10, and then re-size it whenever it gets full, something like this:
h5Files = new String[10];
if (linereader = h5Files.size())
{
String[] temp = h5Files;
h5Files = new String[2 * linereader];
for (int i = 0; i < linereader; i++)
{
h5Files[i] = temp[i];
}
}
Either one of these solutions would allow you to initialize the array (or array alternative) in a safe constructor, prior to your try block, such that you can access it if any exceptions are thrown

Here is your problem. Please take a look on digested version of your code with my comments.
String h5Files[]; // here you define the variable. It still is not initialized.
try{
..................
do {
h5Files = new String[linereader]; // here you initialize the variable
} while(i !=-1); // When i = -1 the end of the file has been reached
..................
catch(IOException exc) {
// if you are here the variable is still not initialized
System.out.println("Error reading file.");
}
// you continue reading file even if exception was thrown while opening the file
I think that now the problem is clearer. You try to open the file and count lines. If you succeed you create array. If not (i.e. when exception is thrown) you catch the exception but still continue reading the file. But in this case you array is not initialized.
Now how to fix this?
Actually if you failed to read the file first time you cannot continue. This may happen for example if file does not exist. So, you should either return when first exception is thrown or just do not catch it at all. Indeed there is nothing to do with the file if exception was thrown at any phase. Exception is not return code. This is the reason that exceptions exist.
So, just do not catch exceptions at all. Declare your method as throws IOException and remove all try/catch blocks.

I need to contain all matches of a Regex into a text file; I'm new to java programming

I'm trying to contain all matches found into a text document, I have been banging my head on my desk for the past 3 hours and figured it would be time I asked for help.
My current issue is with the List<String> and I'm not sure if it because the information entered is wrong or if it's my file print methods. It does not print to file and with other means of printing such as writer.println(returnvalue) and even then, it still only displays one of the matches and not all, I do have the matches appearing in console just to make sure they are showing and they are.
Edit2: Sorry this would be my first question on stackoverflow, I guess my question is How would you print all the data from a list array to a text file?
Edit3: My newest problem is printing out all matches i am currently stuck printing out the last match, any advice?
public static void RegexChecker(String TheRegex, String line){
String Result= "";
List<String> returnvalue = new ArrayList<String>();
Pattern checkRegex = Pattern.compile(TheRegex);
Matcher regexMatcher = checkRegex.matcher(line);
int count = 0 ;
FileWriter writer = null;
try {
writer = new FileWriter("output.txt");
} catch (IOException e1) {
e1.printStackTrace();
}
while ( regexMatcher.find() ){
if (regexMatcher.group().length() != 0){
returnvalue.add(regexMatcher.group());
System.out.println( regexMatcher.group().trim() );
}
for(String str: returnvalue) {
try {
out.write(String.valueOf(returnvalue.get(i)));
writer.write(str);
} catch (IOException e) {
e.printStackTrace();
}
}
}
}

Get the for out of while. You want to write to the file only after all matches have been added to the list. The for-each block needs some modifications as well.
The for-each construct gives you values from iteration over the collection. You need not obtain the values again using an index.
Try this:
while (regexMatcher.find()) {
if (regexMatcher.group().length() != 0) {
returnvalue.add(regexMatcher.group());
System.out.println(regexMatcher.group().trim());
}
}
try {
for (String str : returnvalue) {
writer.write(str + "\n");
}
writer.flush();
writer.close();
} catch (IOException e) {
e.printStackTrace();
}