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.

Reading and splitting data from a text file

So I have a text file that looks like this...
4234
Bob
6858
Joe
I am trying to read the file with java and insert the data into an array. I want to separate the data by that empty line (space). Here is the code that I have come up with to solve the issue, but I am not quite there.
public class Main {
public static void main(String[] args) {
// This name is used when saving the file
BufferedReader input;
String inputLine;
try {
input = new BufferedReader(new FileReader("test.txt"));
while ((inputLine = input.readLine()) != null) {
System.out.println(Arrays.toString(inputLine.split(" ")));
}
} catch (IOException e) {
System.out.println(e.getMessage());
System.exit(1);
}
}
}
The issue that I am coming across is that the output from the code above looks something like this
[4234]
[Bob]
[]
[6858]
[Joe]
The outcome that I would like to achieve, and for the life of me can't think of how to accomplish, is
[4234, Bob]
[6858, Joe]
I feel like with many things that it is a relatively simple code change; I am just not sure what that is.

You need:
2D array
Logic to keep track of where you are in the array position
If your Line is a Number/String
This sounds like hw :) so I wont be solving it, I will just help a bit.
String[][] myData = define your 2D array;
//You need to create a consumer. This is what will take the String line, figure out where to put it into your 2D array.
Consumer<String> processLine = (line) -> {
if(StringUtils.isNumeric(line)){
//Put into array[counter][1]
}
else{
//its a String
//Put into array[counter][0]
}
};
The below try/catch, Opens a File, Reads its Lines, and goes over each one in order (forEachOrdered), ignoring all empty lines, and send it to your processLine consumer.
try (Stream<String> lines = Files.lines(Paths.get("C:/example.txt"), Charset.defaultCharset())) {
lines.filter(line -> !line.isEmpty()).forEachOrdered(processLine);
}
catch (Exception e){
//Handle Exception
}
Used Apache StringUtils http://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/StringUtils.html
IF you dont want to use any external Libs. You can probably do
Integer.parseInt(line) <-- If that throws an exception, its not a number

Your way of reading the file is not most convenient, in this case.. Scanner would have eased all this work; however, if you insist, that you want to use BufferedReader and FileReader, it's going to be a bit verbose, boilerplate and even ugly code, something like this:
public class Main {
public static void main(String[] args) {
// This name is used when saving the file
BufferedReader input;
String inputLine;
String answer = "";
try {
input = new BufferedReader(new FileReader("path\\to\\your\\test.txt"));
while ((inputLine = input.readLine()) != null) {
answer = answer + "[" + inputLine + ", ";
while ((inputLine = input.readLine()) != null && !inputLine.equals("")) {
answer += inputLine;
}
answer += "]";
System.out.println(answer);
answer = "";
}
} catch (IOException e) {
System.out.println(e.getMessage());
System.exit(1);
}
}
}
This code, with test.txt containing:
4234
Bob
6858
Joe
4234
John
5352
Martin
will output:
[4234, Bob]
[6858, Joe]
[4234, John]
[5352, Martin]

I don't know if it's an actual requirement for you to use arrays of strings, but the better way in the long run is to create a class.
class Person {
public String id;
public String name;
public String toString() { return String.format("[%s, %s]", id, name); }
}
(note: It's a bad idea to actually make the fields public, but this makes the code shorter. You should probably use getters and setters).
Now you can create Persons while reading the file.
List<Person> allInFile = new ArrayList<>();
try (BufferedReader reader = new BufferedReader(new FileReader("path\\to\\your\\test.txt"))) {
String line = reader.readLine();
while (line != null) {
line = line.trim();
// ignore empty lines
if (line.length() == 0) {
continue;
}
// this is an id; create a person and assign id
Person person = new Person();
person.id = line;
// read consecutive field, which is the name
person.name = reader.readLine();
// add the person to the list
allInFile.add(person);
}
}
allInFile.forEach(System.out::println);
Lots of improvements to be done on this, but the main point is to put the two data points into a class.

Try with this code:
it work only when file contains number followed by name otherwise pair would be different format
pair : [number, string]
public static void main(String[] args) {
BufferedReader input;
String inputLine;
List<String> pair = new ArrayList<String>();
List<String> list = new ArrayList<String>();
try {
input = new BufferedReader(new FileReader("Test.txt"));
while ((inputLine = input.readLine()) != null) {
if (!inputLine.isEmpty()) {
pair.add(inputLine);
}
if (pair.size() == 2) {
list.add(pair.toString());
pair.clear();
}
}
for (String s : list) {
System.out.println(s);
}
} catch (IOException e) {
System.out.println(e.getMessage());
System.exit(1);
}
}

After looking at the answers posted by my fellow Stack Overflow members I figured out that there was a very simple way of solving this issue and that was by using Scanner rather than using BufferedReader. I am not sure why I didn't think of this before, but hindsight is 2020. Anyway, the code below is what I used to solve my issue.
public static void main(String[] args) {
ArrayList<String> test = new ArrayList<>();
File file = new File("test.txt");
try {
Scanner sc = new Scanner(file);
while (sc.hasNextLine()) {
test.add(sc.next()); // The id
test.add(sc.next()); // The name
}
sc.close();
System.out.println(test.toString());
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
All this is doing is getting each line with the different data on it and is skipping the blank. From there it is adding it to an ArrayList for later processing. Remember K.I.S.S (Keep It Simple Stupid) no need to overcomplicate anything.

Combine a Read and Parse text.txt

Problem: I can't parse my file test.txt, by spaces. I can 1) read text files, and I can 2) parse strings, but I cannot connect the two and parse a text file! My purpose is to learn how to analyze text files. This is a simplified approach to that.
Progress: Thus far, I can read test.txt using FileReader and BufferedReader, and print it to console. Further, I can parse simple String variables. The individual operations run, but I'm struggling with parsing an actual text file. I believe this is because my test.txt is stored in the buffer, and after I .close() it, I can't print it.
Text File Content:
This is a
text file created, only
for testing purposes.
Code:
import java.io.*;
public class ReadFile {
//create method to split text file, call this from main
public void splitIt(String toTest)
{
String[] result = toTest.split(" ");
for (String piece:result)
{
//loop through the array and print each piece
System.out.print(piece);
}
}
public static void main(String[] args) {
//create readfile method
try
{
File test = new File("C:\\final\\test.txt");
FileReader fileReader = new FileReader(test);
BufferedReader reader = new BufferedReader(fileReader);
String line = null;
//While there are still lines to be read, read and print them
while((line = reader.readLine()) != null)
{
System.out.println(line);
splitIt(line);
}
reader.close();
}
//Catch those errors!
catch (Exception ex)
{
ex.printStackTrace();
}
// readFileMethod a = new readFileMethod(line);
System.out.println(a.splitIt());
}
}
Preemptive thank you for your sharing your knowledge. Many posts on reading and parsing have been solved here on SO, but I've not the understanding to implement others' solutions. Please excuse me, I've only been learning Java a few months and still struggle with the basics.

Ok lets make the splitting into a mthod
private static void splitIt (String toTest) {
String[] result = toTest.split(" ");
for (String piece:result)
{
//loop through the array and print each piece.
System.out.println(piece);
}
}
then you can call it from within
while((line = reader.readLine()) != null)
{
System.out.println(line);
splitIt (line);
}

Building on Scary Wombat and your code, i made some changes.
It should now print the Line that is being read in and each word that is separated by space.
import java.io.*;
public class ReadFile {
//create method to split text file, call this from main
public static void splitIt(String toTest)
{
String[] result = toTest.split(" ");
for (String piece:result)
{
//loop through the array and print each piece
System.out.println(piece);
}
}
public static void main(String[] args) {
//create readfile method
try
{
File test = new File("C:\\final\\test.txt");
FileReader fileReader = new FileReader(test);
BufferedReader reader = new BufferedReader(fileReader);
String line = null;
//While there are still lines to be read, read and print them
while((line = reader.readLine()) != null)
{
System.out.println(line); // print the current line
splitIt(line);
}
reader.close();
}
//Catch those errors!
catch (Exception ex)
{
ex.printStackTrace();
}
}
}

How to search a word in file in java

I am trying to search a string in a file in java and this is what, I tried . In the below program I am getting output as No Data Found and I am sure that the file has the word which I am searching
import java.io.*;
import java.util.Scanner;
public class readfile {
static String[] list;
static String sear = "CREATE";
public void search() {
Scanner scannedFile = new Scanner("file.txt");
while (scannedFile.hasNext()) {
String search = scannedFile.next();
System.out.println("SEARCH CONTENT:"+search);
if (search.equalsIgnoreCase(sear)) {
System.out.println("Found: " +search);
}
else {
System.out.println("No data found.");
}
}
}
public static void main (String [] args) throws IOException {
readfile read = new readfile();
read.search();
}
}

Don't do:
search.equalsIgnoreCase(sear)
Try:
search.toUpperCase().contains(sear)
I think the search is the whole String of the File, so you never would become true with equals.

Use nextLine() instead of next() and then use split. Like this :
What's the difference between next() and nextLine() methods from Scanner class?
Difference :
next() can read the input only till the space. It can't read two words separated by space. Also, next() places the cursor in the same line after reading the input.
nextLine() reads input including space between the words (that is, it reads till the end of line \n). Once the input is read, nextLine() positions the cursor in the next line.
Use following code :
String search = scannedFile.nextLine();
String[] pieces = data.split("\\s+");
for(int i=0; i<pieces.length(); i++)
{
if(pieces[i].equalsIgnoreCase(sear))
{
System.out.println("Found: " +search);
}
else
{
System.out.println("No data found.");
}
}

Ok, here is my understanding of your program.
You search in the file file.txt the word CREATE.
To do so, you read each word in the file and if it is CREATE you print Found create.
The issue here is that for every word in the file, if it isn't CREATE you print No data found.
Instead you should wait for the end of the file and then if you haven't found it you will print the error message.

Try this :
import java.io.*;
import java.util.ArrayList;
import java.util.List;
public class readfile {
static String[] list;
static String sear = "CREATE";
public void search() throws IOException {
List<String> saveAllLinesForRewriting = new ArrayList<String>();
// Need to read file line by line
BufferedReader bufferedReader = new BufferedReader(new FileReader("file.txt"));
String saveLine;
while ((saveLine = bufferedReader.readLine()) != null) {
saveAllLinesForRewriting.add(saveLine);
}
bufferedReader.close();
// Check if your word exists
if (saveAllLinesForRewriting.toString().contains(sear)) {
System.out.println("Found: " + sear);
} else {
System.out.println("No data found.");
}
}
public static void main(String[] args) throws IOException {
readfile read = new readfile();
read.search();
}
}

Instead of reading file using scanner, first create a file resource to read by adding the below line
File file = new File("Full Path of file location");
before
Scannner scannedfile = new Scanner("file.txt");
and change the above line to
Scanner scannedfile = new Scanner(file);
rest your code is working fine.

The problem is that the scanner is scanning the String "file.txt" and not the file.
To fix this you have to do what amit28 says. Your finally code is as follows
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.Scanner;
public class readfile {
static String[] list;
static String sear = "CREATE";
public void search() {
File f = new File("file.txt");
Scanner scannedFile;
try {
scannedFile = new Scanner(f);
while (scannedFile.hasNext()) {
String search = scannedFile.next();
System.out.println("SEARCH CONTENT:"+search);
if (search.equalsIgnoreCase(sear)) {
System.out.println("Found: " +search);
}
else {
System.out.println("No data found.");
}
}
} catch (FileNotFoundException e) {
// FIXME Auto-generated catch block
e.printStackTrace();
}
}
public static void main (String [] args) throws IOException {
readfile read = new readfile();
read.search();
}
}

Java: Methods, Files, and Arrays

I'm supposed to be coding an app that can read names from a hardcoded text file, save them as a string array, then write those names in a different text file but sorted. I believe I have the first two parts down but I'm confused on how to sort the names then write them into a new file.
These is the actual problem I'm working on:
"Take an input file with 10 names in it (hard coded). Write a program to read the file, save the names in a String array and write into a different file names in sorted order. Use Methods appropriately."
BTW I'm a rookie coder, this is what I have so far.
public static void main(String[] args) throws FileNotFoundException {
// TODO code application logic here
readFile();
saveStringArray();
}
public static void readFile() {
File file = new File("/Users/nicoladaaboul/Desktop/Programming/C++, "
+ "HTML5, Java, PHP/Java/Question2/names.txt");
try {
Scanner sc = new Scanner(file);
while (sc.hasNextLine()) {
String i = sc.next();
}
sc.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
public static void saveStringArray() throws FileNotFoundException {
String token1 = "";
Scanner inFile1 = new Scanner(new File("names.txt")).useDelimiter(",\\s*");
List<String> temps = new ArrayList<String>();
while (inFile1.hasNext()) {
token1 = inFile1.next();
temps.add(token1);
}
inFile1.close();
String[] tempsArray = temps.toArray(new String[0]);
Arrays.sort(tempsArray);
for (String s : tempsArray) {
System.out.println(s);
}
}
public static void sortingNames() {
}
public static void writingFile() throws FileNotFoundException {
PrintWriter writer = new PrintWriter("sortedNames.txt");
writer.close();
}

Its important that you break your problem down into instructions.
1. You need to read the file you can use bufferedReader(code below).
2. Create an array(or arraylist) to store your string values.
3. Then as you read each line, store these values in the array.
4. When finished reading the file you then would pass this array to a function that would sort it(Why does my sorting loop seem to append an element where it shouldn't?).
5. Once sorted you simply write this array, to a file.
BufferedReader br = new BufferReader(new FileReader("name.txt"));
int count = 0;
String line;
String[] names = new String[100];
while((line = br.nextLine()) != null){
names[count] = line;
count++;
}