Develop Reference

algorithm arraylist remove String duplicates and save to new text file

I am currently writing an algorithm that creates an ArrayList from a .txt file, checks it with a loop for duplicates (where the loop should look like this:
Line one is written to new .txt & boolean found is set to true because the string was already found.
Line 2 is written to new .txt etc.
But if two strings are identical, the duplicate, i.e. the second string should just be ignored and continue with the next one).
public class test {
public static void main(String[] args) throws IOException {
String suche = "88 BETRAG-MINUS VALUE 'M'.";
String suche2 = "88 BETRAG-PLUS VALUE 'P'";
boolean gefunden = false;
File neueDatei = new File("C:\\Dev\\xx.txt");
if (neueDatei.createNewFile()) {
System.out.println("Datei wurde erstellt");
}
if (gefunden == false) {
dateiEinlesen(null, gefunden);
ArrayList<String> arr = null;
inNeueDateischreiben(neueDatei, gefunden, arr, suche, suche2);
}
}
public static void dateiEinlesen(File neueDatei, boolean gefunden) {
BufferedReader reader;
String zeile = null;
try {
reader = new BufferedReader(new FileReader("C:\\Dev\\Test.txt"));
zeile = reader.readLine();
ArrayList<String[]> arr = new ArrayList<String[]>();
while (zeile != null) {
arr.add(zeile.split(" "));
zeile = reader.readLine();
}
System.out.println(arr);
} catch (IOException e) {
System.err.println("Error2 :" + e);
}
}
public static void inNeueDateischreiben(File neueDatei, boolean gefunden, ArrayList<String> arr, String suche2,
String suche22) throws IOException {
FileWriter writer = new FileWriter(suche22);
String lastValue = null;
for (Iterator<String> i = arr.iterator(); i.hasNext();) {
String currentValue = i.next();
if (lastValue != null && currentValue.equals(lastValue)) {
i.remove();
{
writer.write(suche2.toString());
gefunden = true;
}
}
writer.close();
}
}
}

Your variable namings (suche2, suche22) makes reading the code difficult.
Other than that, your writing algorithm looks funny. You only compare adjacent lines while duplicate lines could be anywhere. In addition, writer.write only hits when you find a duplicate. Also how you call it and other things don't look right.
Here are some general steps to write this correctly:
Open the file so you can read it line by line.
Create a file writer
Create a set or dictionary like data structure that enables you to look up items in constant time.
For each line that you read do the following:
Look if the line exists in the dictionary.
If not, write it to the new file
If it already exists in the dictionary, skip to step 4.
Add that line to the dictionary for later comparisons and go to step 4.
When the lines are exhausted close both files.
I suggest, you rewrite your code completely as the current version is very difficult to amend.

Java program that concatenates the contents of several files into one file...?

I'm writing a java program that I'm running on the CMD line that copies several .txt files into one. For example I have three .txt files that I created. Chapter1.txt, chapter2.txt Chapter3.txt. All the contents of these files needs to be copied to book.txt. I ran the code and it ran fine until I entered the command.
java CatFiles chapter1.txt chapter2.txt chapter3.txt book.txt
The book.txt file is created but only the contents of one file are copied and I get this error code
java.land.illeglStateException: Scanner
at java.util.Scanner.ensureOpen(unknown Source)
at java.util.Scanner.findWithinHorizon(unknown Source)
at java.util.Scanner.hasNextLine(unknown Source)
at CatFiles.main(CatFiles.java)
Here's my code
public class CatFiles {
public static void main(String[] args) throws IOException {
if (args.length < 2) {
System.out.println("Usage: CatFiles sourcefile1 sourcefile2 . . . targetfile");
return;
}
String target = args[args.length - 1];
FileReader reader = null;
PrintWriter out = new PrintWriter(target);
for (int i = 0; i < args.length - 1; i++) {
String source = args[i];
reader = new FileReader(source);
}
Scanner in = new Scanner(reader);
while ( in .hasNextLine()) {
try {
String line = in .nextLine();
out.println(line);
} finally { in .close();
out.close();
}
}
}
}

Use this (note: checks about arguments are left as an exercise):
public static void main(final String... args)
{
final List<String> list = new ArrayList<>();
Collections.addAll(list, args);
final Path dstFile = Paths.get(list.remove(list.size() - 1));
try (
final OutputStream out = Files.newOutputStream(dstFile);
) {
for (final String s: list)
Files.copy(Paths.get(s), out);
}
}

You should put the while loop inside of the try block and not the contrary. Otherwise you're closing the Scanner at the first loop and you can not use it anymore. Close your Scanner once you're never using it again.
I honestly think correct indentation would have helped here.
JavaDoc
Throws: NoSuchElementException if no line was found
java.lang.IllegalStateException if this scanner is closed
Solution
Scanner in = new Scanner(reader);
try{
while (in.hasNextLine()) {
String line = in.nextLine();
out.println(line);
}
} finally {
in.close();
out.close();
}

Idiomatic Solution using Guava:
This includes basic error checking on valid number of arguments. This does not do robust idiomatic exception handling for brevity and scope control.
This solution also uses Immutable data throughout making it immune to logic errors because of side effects and state mutation.
Q33846584.java
Import statements are available in the link above.
public class Q33846584
{
public static void main(final String[] args) throws Exception
{
checkArgument(args.length > 2, "You must supply at least 3 file paths as arguments dest, src, src, ...");
final List<Path> paths = Lists.transform(Arrays.asList(args), new Function<String, Path>()
{
#Nullable #Override public Path apply(#Nullable String input)
{
return Paths.get(checkNotNull(input));
}
});
final Path destination = paths.get(0);
try (final OutputStream fos = new FileOutputStream(destination.toFile()))
{
for (final Path p : paths.subList(1, paths.size()))
{
if (p.toFile().exists())
{
System.out.format("Reading %s and writing to %s", p.toAbsolutePath(), destination.toAbsolutePath());
final FileInputStream fis = new FileInputStream(p.toFile());
ByteStreams.copy(fis, fos);
System.out.println();
}
else
{
System.err.format("%s does not exist skipping!", p.toAbsolutePath());
System.err.println();
}
}
}
}
}
Without Guava:
You would have to implement the transformation of the String[] yourself in a imperative loop which is straightforward.
You would have to implement copying the InputStream to the OutputStream which is well documented on the internet in general but is basically boilerplate code. You will end up with a possibly buggy or inefficient version of what Guava does. It would only be useful as a learning exercise at best.
Both of these activities are easy to find on Stackoverflow and are left as exercises for the reader.

Creating objects from text file input

I'm still very new to java. I am trying to create an array of objects from a text file. The text file has a list of names, and using these names, I'm trying to create objects. This is the method I've created to create the objects from the text file input. It gives an error when compiled. I'm not sure where I've done wrong.
public boolean createObjects(PersonNames2[] person) throws Exception
{
boolean found = false;
int position = 0;
if(canCreateObjects() == true)
{
for(int i = 0; i < persons.length && !found; i++)
{
if(persons[i] == null)
{
position = i;
found = true;
}
}
Scanner reader = new Scanner(file);
while(reader.hasNext())
{
person[position] = new PersonNames2();
position++;
}
reader.close();
return true;
}
return false;
}

error: array dimension missing PersonNames person[] = new Person[];
That's clearly telling that you are failed to give the size of your array.
You need to write
PersonNames person[] = new Person[size]; // For ex : 10 or any X
Array's are fixed in size and you need to tell the size of it while declaring/initializing it self.
Update:
Since you are reading data from a file and no idea about the length of array, better to choose ArrayList instead of array. Size of the ArrayList increases over the time you add elements to it.

If you are new in Java, than this tiny GitHub project could be a nice set of hints for you.

I've managed to get this working. Thanks! Here is the working code.
public static List<Person> loadPersons(String path) throws Exception
{
BufferedReader reader = new BufferedReader(new FileReader(path));
List<Person> persons = new ArrayList<Person>();
while((line = reader.readLine()) != null)
{
System.out.println("Adding " +line);
persons.add(new Person(line));
}
return persons;
}

How can I read from the next line of a text file, and pause, allowing me to read from the line after that later?

I wrote a program that generates random numbers into two text files and random letters into a third according the two constant files. Now I need to read from each text file, line by line, and put them together. The program is that the suggestion found here doesn't really help my situation. When I try that approach it just reads all lines until it's done without allowing me the option to pause it, go to a different file, etc.
Ideally I would like to find some way to read just the next line, and then later go to the line after that. Like maybe some kind of variable to hold my place in reading or something.
public static void mergeProductCodesToFile(String prefixFile,
String inlineFile,
String suffixFile,
String productFile) throws IOException
{
try (BufferedReader br = new BufferedReader(new FileReader(prefixFile)))
{
String line;
while ((line = br.readLine()) != null)
{
try (PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(productFile, true))))
{
out.print(line); //This will print the next digit to the right
}
catch (FileNotFoundException e)
{
System.err.println("File error: " + e.getMessage());
}
}
}
}
EDIT: The digits being created according to the following. Basically, constants tell it how many digits to create in each line and how many lines to create. Now I need to combine these together without deleting anything from either text file.
public static void writeRandomCodesToFile(String codeFile,
char fromChar, char toChar,
int numberOfCharactersPerCode,
int numberOfCodesToGenerate) throws IOException
{
for (int i = 1; i <= PRODUCT_COUNT; i++)
{
int I = 0;
if (codeFile == "inline.txt")
{
for (I = 1; I <= CHARACTERS_PER_CODE; I++)
{
int digit = (int)(Math.random() * 10);
try (PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(codeFile, true))))
{
out.print(digit); //This will print the next digit to the right
}
catch (FileNotFoundException e)
{
System.err.println("File error: " + e.getMessage());
System.exit(1);
}
}
}
if ((codeFile == "prefix.txt") || (codeFile == "suffix.txt"))
{
for (I = 1; I <= CHARACTERS_PER_CODE; I++)
{
Random r = new Random();
char digit = (char)(r.nextInt(26) + 'a');
digit = Character.toUpperCase(digit);
try (PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(codeFile, true))))
{
out.print(digit);
}
catch (FileNotFoundException e)
{
System.err.println("File error: " + e.getMessage());
System.exit(1);
}
}
}
//This will take the text file to the next line
if (I >= CHARACTERS_PER_CODE)
{
{
Random r = new Random();
char digit = (char)(r.nextInt(26) + 'a');
try (PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(codeFile, true))))
{
out.println(""); //This will return a new line for the next loop
}
catch (FileNotFoundException e)
{
System.err.println("File error: " + e.getMessage());
System.exit(1);
}
}
}
}
System.out.println(codeFile + " was successfully created.");
}// end writeRandomCodesToFile()

Being respectfull with your code, it will be something like this:
public static void mergeProductCodesToFile(String prefixFile, String inlineFile, String suffixFile, String productFile) throws IOException {
try (BufferedReader prefixReader = new BufferedReader(new FileReader(prefixFile));
BufferedReader inlineReader = new BufferedReader(new FileReader(inlineFile));
BufferedReader suffixReader = new BufferedReader(new FileReader(suffixFile))) {
StringBuilder line = new StringBuilder();
String prefix, inline, suffix;
while ((prefix = prefixReader.readLine()) != null) {
//assuming that nothing fails and the files are equals in # of lines.
inline = inlineReader.readLine();
suffix = suffixReader.readLine();
line.append(prefix).append(inline).append(suffix).append("\r\n");
// write it
...
}
} finally {/*close writers*/}
}
Some exceptions may be thrown.
I hope you don't implement it in one single method.
You can make use of iterators too, or a very simple reader class (method).
I wouldn't use List to load the data at least I guarantee that the files will be low sized and that I can spare the memory usage.

My approach as we discussed by storing the data and interleaving it. Like Sergio said in his answer, make sure memory isn't a problem in terms of the size of the file and how much memory the data structures will use.
//the main method we're working on
public static void mergeProductCodesToFile(String prefixFile,
String inlineFile,
String suffixFile,
String productFile) throws IOException
{
try {
List<String> prefix = read(prefixFile);
List<String> inline = read(inlineFile);
List<String> suffix = read(productFile);
String fileText = interleave(prefix, inline, suffix);
//write the single string to file however you want
} catch (...) {...}//do your error handling...
}
//helper methods and some static variables
private static Scanner reader;//I just prefer scanner. Use whatever you want.
private static StringBuilder sb;
private static List<String> read(String filename) throws IOException
{
List<String> list = new ArrayList<String>;
try (reader = new Scanner(new File(filename)))
{
while(reader.hasNext())
{ list.add(reader.nextLine()); }
} catch (...) {...}//catch errors...
}
//I'm going to build the whole file in one string, but you could also have this method return one line at a time (something like an iterator) and output it to the file to avoid creating the massive string
private static String interleave(List<String> one, List<String> two, List<String> three)
{
sb = new StringBuilder();
for (int i = 0; i < one.size(); i++)//notice no checking on size equality of words or the lists. you might want this
{
sb.append(one.get(i)).append(two.get(i)).append(three.get(i)).append("\n");
}
return sb.toString()
}
Obviously there is still some to be desired in terms of memory and performance; additionally there are ways to make this slightly more extensible to other situations, but it's a good starting point. With c#, I could more easily make use of the iterator to make interleave give you one line at a time, potentially saving memory. Just a different idea!

Counting values in a column of a .csv file Java

I'm tasked, by my professor, to write a program to read a .csv file (778 rows (including header row), 8 columns).
I need to:
1. Write a method to receive the name of the file as its argument and then print the number of lines in the file.
public void printNumberOfLinesInFile(String fileName)
Write a method to receive the name of the file as its argument and then print the number of private and non-private colleges.
public void printNumberOfPrivateNonPrivateCollegesInFile(String fileName)
Write a method to receive the name of the file as its argument and then print the private college name with largest out of state tuition.
public void printMostExpensivePrivateCollegeInFile(String fileName)
Write a method to receive the name of the file as its argument and then print the non-private college with largest out of state tuition.
public void printMostExpensiveNonPrivateCollegeInFile(String fileName)
Write a method to receive the name of the file as its argument and then print the number of applications and the number of applicants that are accepted for private and non-private colleges.
public void printNumberOfApplications(String fileName)
Write a method to receive the name of the file as its argument and then print following information for private and non-private colleges.
Average of expenses for books.
Average of expenses for room.
Average of personal expenses.
public void printAverageOfExpenses(String fileName)
Disclaimer: I do not want anyone to do my homework for me. I need to learn so I can apply my knowledge when I graduate and enter industry. I'm simply asking for a hint or a better way at writing the code.
My code thus far:
public class Week14
{
public String data;
public void printNumberOfLinesInFile(String inFile) throws IOException
{
int collegeCount = 0;
FileReader fileRead = new FileReader(inFile);
BufferedReader bufferRead = new BufferedReader(fileRead);
while(true)
{
String line = bufferRead.readLine();
if(line == null)
{
break;
}
collegeCount++;
//System.out.println(line);
}
System.out.println(collegeCount-1 + " Colleges total.");
}
public void printNumberOfPrivateNonPrivateCollegesInFile(String inFile) throws IOException
{
int privateCount = 0;
int nonprivateCount = 0;
int count = 0;
FileReader fileRead = new FileReader(inFile);
BufferedReader bufferRead = new BufferedReader(fileRead);
while((data = bufferRead.readLine())!= null)
{
String line = bufferRead.readLine();
String [] lineItems = line.split(",");
for(int i = 0; i < line.length(); i++)
{
if(lineItems[i].equals("Yes"))
{
privateCount++;
}
}
break;
}
System.out.println(privateCount+" private Colleges.");
System.out.println(nonprivateCount+ " non-private Colleges.");
}
public void printMostExpensivePrivateCollegeInFile(String inFile) throws FileNotFoundException, IOException
{
int mostExpensive = 0;
int currentExpensive = 0;
FileReader fileRead = new FileReader(inFile);
BufferedReader bufferRead = new BufferedReader(fileRead);
while((data = bufferRead.readLine())!= null)
{
String line = bufferRead.readLine();
if(line.equals("OutstateTuition"))
{
System.out.println(line);
}
else
{
System.out.println(line);
}
}
}
public void printMostExpensiveNonPrivateCollegeInFile(String fileName)
{
}
public void printNumberOfApplications(String fileName)
{
}
public void printAverageOfExpenses(String fileName)
{
}
public static void main(String[] args) throws FileNotFoundException, IOException
{
File inFile = new File("College.csv");
FileReader fileReader = new FileReader(inFile);
BufferedReader buffReader = new BufferedReader(fileReader);
Week14 w1 = new Week14();
//w1.printNumberOfLinesInFile("College.csv");
w1.printNumberOfPrivateNonPrivateCollegesInFile("College.csv");
//^^^The above line goes into an infinite loop^^^
//w1.printMostExpensivePrivateCollegeInFile("College.csv");
}
}
The problem is, I'm stuck on trying to count the amount of private and nonprivate colleges. In my method, printNumberOfPrivateNonPrivateCollegesInFile (line 39), I'm running into an exception: java.lang.ArrayIndexOutOfBoundsException: 8
I've asked my professor how I can avoid this, I've looked online and the problem seems to lie with the iterator int 'i'. I'm trying to traverse the array, and 'i' is out of bounds. When I put a '1' in
if(lineItems[i].equals("Yes"))
for my privateCount, there is an output of 67 from privateCount, (I think it is counting the individual characters for some reason).
My question, what would be the most effective way to traverse the entire .csv file, and to access individual columns so I can count them and output them?
Any help would be greatly appreciated.
edit:
I have changed the while loop:
while(true)
{
String line = bufferRead.readLine();
String [] lineItems = line.split(",");
if(line == null)
{
break;
}
for (String lineItem : lineItems) {
privateCount++;
}
}
Now I can traverse the entire .csv file, but I'm receiving a java.lang.NullPointerException when I try and count.
edit 2:
I've redone my while loop again,
while(true)
{
String line = bufferRead.readLine();
String [] lineItems = line.split(",");
for (String lineItem : lineItems) {
if (lineItem.equals("Yes")) {
privateCount++;
}
}
System.out.println(privateCount);
}
I'm now counting the right value for privateCount, but there's a NullPointerException at :
String [] lineItems = line.split(",");
and the loop will not let me put my 'echo' outside of the while-loop without a 'break' statement.

With respect to actual industry-level code, and assuming that assignment did not specifically focus on actual CSV decoding, I would recommend finding and using a library to handle low-level decoding, such as OpenCSV, SuperCSV or CSV-module for Jackson.
This way your code can focus on more interesting part of finding specific values, and not on intricate details like possible escaping and/or quoting of contents.
If the focus is on CSV edge cases this is not the approach to use; but for real production code one hopefully rarely if ever writes the actual low-level decoding part, given the existence of multiple good libraries for the task.

if(lineItems != null && lineItems.length>0){
// do your loop
}
if (lineItem!= null && !lineItem.trim().equals("") && lineItem.equals("Yes")) {
privateCount++;
}
most likely will prevent your null issue

public void printNumberOfPrivateNonPrivateCollegesInFile(String inFile) throws IOException
{
int privateCount = 0;
int nonprivateCount = 0;
FileReader fileRead = new FileReader(inFile);
BufferedReader bufferRead = new BufferedReader(fileRead);
try
{
while(true)
{
String line = bufferRead.readLine();
String [] lineItems = line.split(",");
//System.out.println(Arrays.toString(lineItems));
for (String lineItem : lineItems)
{
if (lineItem!= null && !lineItem.trim().isEmpty() && lineItem.equals("No"))
{
nonprivateCount++;
}
if (lineItem!= null && !lineItem.trim().isEmpty() && lineItem.equals("Yes"))
{
privateCount++;
}
}
//System.out.println(privateCount);
}
}
catch(NullPointerException npe)
{
}
System.out.println(privateCount);
System.out.println(nonprivateCount);
}
Fixed it. I'm now just catching the exception so it isn't as annoying. Thanks all for the help.