Develop Reference

How can I remove specific elements from a linkedlist in java based on user input?

I'm very new (6 weeks into java) trying to remove elements from a csv file that lists a set of students as such (id, name, grades) each on a new line.
Each student id is numbered in ascending value. I want to try and remove a student by entering the id number and I'm not sure how I can do this.
So far I've just tried to reduce the value that user inputs to match the index as students are listed by number and I did this in a while loop. However, each iteration doesn't recognize the reduction from the previous user Input, and I think I need a way that can just search the value of the id, and remove the entire line from the csv file.
Have only tried to include the pertinent code. Reading previous stack questions has shown me a bunch of answers related to nodes, which make no sense to me since I don't have whatever prerequisite knowledge is required to understand it, and I'm not sure the rest of my code is valid for those methods.
Any ideas that are relatively simple?
Student.txt (each on a new line)
1,Frank,West,98,95,87,78,77,80
2,Dianne,Greene,78,94,88,87,95,92
3,Doug,Lei,78,94,88,87,95,92
etc....
Code:
public static boolean readFile(String filename) {
File file = new File("C:\\Users\\me\\eclipse-workspace\\studentdata.txt");
try {
Scanner scanner = new Scanner(file);
while(scanner.hasNextLine()) {
String[] words=scanner.nextLine().split(",");
int id = Integer.parseInt(words[0]);
String firstName = words[1];
String lastName = words[2];
int mathMark1 = Integer.parseInt(words[3]);
int mathMark2 = Integer.parseInt(words[4]);
int mathMark3 = Integer.parseInt(words[5]);
int englishMark1 = Integer.parseInt(words[6]);
int englishMark2 = Integer.parseInt(words[7]);
int englishMark3 = Integer.parseInt(words[8]);
addStudent(id,firstName,lastName,mathMark1,mathMark2,mathMark3,englishMark1,englishMark2,englishMark3);
}scanner.close();
}catch (FileNotFoundException e) {
System.out.println("Failed to readfile.");
private static void removeStudent() {
String answer = "Yes";
while(answer.equals("Yes") || answer.equals("yes")) {
System.out.println("Do you wish to delete a student?");
answer = scanner.next();
if (answer.equals("Yes") || answer.equals("yes")) {
System.out.println("Please enter the ID of the student to be removed.");
//tried various things here: taking userInput and passing through linkedlist.remove() but has never worked.

This solution may not be optimal or pretty, but it works. It reads in an input file line by line, writing each line out to a temporary output file. Whenever it encounters a line that matches what you are looking for, it skips writing that one out. It then renames the output file. I have omitted error handling, closing of readers/writers, etc. from the example. I also assume there is no leading or trailing whitespace in the line you are looking for. Change the code around trim() as needed so you can find a match.
File inputFile = new File("myFile.txt");
File tempFile = new File("myTempFile.txt");
BufferedReader reader = new BufferedReader(new FileReader(inputFile));
BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile));
String lineToRemove = "bbb";
String currentLine;
while((currentLine = reader.readLine()) != null) {
// trim newline when comparing with lineToRemove
String trimmedLine = currentLine.trim();
if(trimmedLine.equals(lineToRemove)) continue;
writer.write(currentLine + System.getProperty("line.separator"));
}
writer.close();
reader.close();
boolean successful = tempFile.renameTo(inputFile);

change specific text in text file with scanner class (java)

I write this code that can search for the some specific text (such as word) in the text file with scanner class, but i want also to replace (old text to the new text) in the same old text locuation.
i find in the internet that i must used replaceAll method like ( replaceAll(old, new); )
but it does't work with the scanner class.
This is my code, it just search (if it existed ) write new text in new line without change the old one.
Do i need to change the method (to get the data) form scanner to FileReader ??
File file = new File("C:\\Users....file.txt");
Scanner input = new Scanner(System.in);
System.out.println("Enter the content you want to change:");
String Uinput = input.nextLine();
System.out.println("You want to change it to:");
String Uinput2 = input.nextLine();
Scanner scanner = new Scanner(file).useDelimiter(",");
BufferedWriter writer = new BufferedWriter(new FileWriter(file, true));
while (scanner.hasNextLine()) {
String lineFromFile = scanner.next();
if (lineFromFile.contains(Uinput)) {
lineFromFile = Uinput2;
writer.write(lineFromFile);
writer.close();
System.out.println("changed " + Uinput + " tO " + Uinput2);
break;
}
else if (!lineFromFile.contains(Uinput)){
System.out.println("Don't found " + Uinput);
break;
}
}

You cannot read from a file, then write to that same file. You need 2 different files.
while (read line from input file) {
if (NOT matches your search pattern)
write line to output file.
else { // matches
write start of line to your search pattern.
write your replace string
write from end of search pattern to end of line.
}
}
Unless your replace string is the same size as your search string, yes, you'll have to use 2 files. Consider the file:
Blah
Blah
Blah
Now replace the letter 'a' with "The quick Brown Fox". If you replace the first line, you've overwritten the rest of the file. Now you can't read the 2nd line, so YES, you'll have to use 2 files.

Here's another answer based on #Sedrick comment and your code.
I'm adding it to your pseudo code.
File file = new File("C:\\Users....file.txt");
Scanner input = new Scanner(System.in);
System.out.println("Enter the content you want to change:");
String Uinput = input.nextLine();
System.out.println("You want to change it to:");
String Uinput2 = input.nextLine();
Scanner scanner = new Scanner(file).useDelimiter(",");
java.util.List<String> tempStorage = new ArrayList<>();
while (scanner.hasNextLine()) {
String lineFromFile = scanner.next();
tempStorage.add(lineFromFile);
}
// close input file here
// Open your write file here (same file = overwrite).
// now loop through temp storage searching for input string.
for (String currentLine : tempStorage ) {
if (!lcurrentLine.contains(Uinput)){
String temp = currentLine.replace(Uinput, Uinput2);
write a line using temp variable
} else { // not replaced
write a line using currentLine;
}
// close write file here
By the way, you'll have to encase the reads writes with try catch to trap for IOExceptions. That's how I knew it was pseudo code. There are plenty of examples for reading/writing a file on this web site. It's easy to search for.

Trying to get Scanner to scan entire file

String userInput = stdin.nextLine();
file = new File(userInput);
Scanner fileScanner = new Scanner(file);
while(fileScanner.hasNext()) {
fileContents = fileScanner.nextLine();
}
So I'm trying to figure out how I can get my variable fileContents to hold all of the file from the scanner. with the current way I have it setup the variable fileContents is left with only the last line of the .txt file. for what I'm doing I need it to hold the entire text from the file. spaces, chars and all.
I'm sure there is a simple fix to this I'm just very new to java/coding.

You need to change
fileContents += fileScanner.nextLine();
or
fileContents =fileContents + fileScanner.nextLine();
With your approach you are reassigning the fileContents value instead you need to concat the next line.

String userInput = stdin.nextLine();
file = new File(userInput);
StringBuilder sb = new StringBuilder();
Scanner fileScanner = new Scanner(file);
while(fileScanner.hasNext()) {
sb.append(fileScanner.nextLine()+"\n");
}
System.out.println(sb.toString());
Or follow the #singhakash's answer, because his one is faster performance wise I presume. But I used a StringBuilder to give you an idea that you're 'appending' or in other words, just adding to the data that you wish to use. Where as with your way, you're going to be getting the last line of the text because it keeps overriding the previous data.

You can use below as well:
Scanner sc = new Scanner(new File("C:/abc.txt"));
String fileContents = sc.useDelimiter("\\A").next();
You don't have to use while loop in this case.

Java: reading content from text file to create an object?

I am attempting to read from a text file similar to:
exampleName1 exampleAddress1
exampleName2 exampleAddress2
How can I create an object with the name and address together by reading each line in a text file?
E.g: Record record1= new Record(name, address);
I have attempted to use Scanner but I am not sure how to exactly.
Scanner myscanner= new Scanner (new FileInputStream(myfile.txt);
while (myscanner.hasnext()){
//read from file?
}
//create object here...

I would do something like this:
List<Record> records = new ArrayList<>();
Scanner myscanner= new Scanner (new FileInputStream("myfile.txt"));
while (myscanner.hasnext()){
String line = myscanner.readline();
int index = line.indexOf(' ');
String name = line.substring(0, index-1);//TODO check...
String address = line.substring(index);
records.add(new Record(name, address);
}
Untested code, but should work (somehow). If you have problems, be more specific with the question.
Edit: of course the scanner has not readline(). Btw. why use a Scanner? With a BufferedReader and a proper InputStreamReader you can do it.
Edit2:
With proper I mean, that you pass the Charset of the file like this: new InputStreamReader("filename", StandardCharsets.UTF_8) (or whatever the Charset of the file is...)

Please search a little bit much more to find out such a simple answer...
Cave of Programming exemple
I would try something like this :
try {
String line;
String[] splitedLine;
String name;
String address;
BufferedReader br = new BufferedReader(new FileReader("myfile.txt"));
while((line=br.readLine()) != null) {
splitedLine = line.split(' ');
name = splitedLine[0];
address = splitedLine[1];
new Record(name,address);
//You could also do new Record(splitedLine[0],splitedLine[1]);
}
} catch (IOException e) {
e.printStackTrace();
}

java program to read all text and eliminating whitespace and line

i want to write a java program to read all the text from a file but without whitespace and lines..suppose given below is all text from a file now i want to read this text and copy it to other file
var provinfo={"cdn":"//bluehost-
cdn.com","domain":"xyz.com","name":"xyz","phone":["(888) 401-4678","(801)
765-9400"],"code":"bh"};
provinfo.cdn = location.protocol + provinfo.cdn;
such that the resultant text in new file is like
varprovinfo{"cdn":"//bluehostcdn.com","domain":"xyz.com","name":"xyz","phone["(888)401-4678","(801)765-9400"],"code":"bh"};provinfo.cdn=location.protocol+provinfo.cdn;
as you can see the text is merged into single line by eliminating whitespace and lines. Thats what i want.
scanner = new Scanner(new File("D://actual.txt"));
String a = scanner.useDelimiter("\\Z").next();
String b= a.replaceAll(" ", "");
String c = b.replaceAll("[\\r\\n]+\\s+", "");
System.out.println(c);
I used this code for writing on console but using the same with fileouputstream does not working?

To eliminate the whitespace there is a very useful and overlooked function
yourString.trim()
However, it wont elimante the lines.

Try this,
Scanner scanner = new Scanner(file);
StringBuilder stringBuilder = new StringBuilder();
while (scanner.hasNext())
{
stringBuilder.append(scanner.next().replaceAll("\\s", "").replaceAll("\n", ""));
}
System.out.println(stringBuilder.toString());

This is working absolutely fine !!! with your above program.
File outputFile = new File("output.txt");
outputFile.createNewFile();
FileOutputStream fileOutputStream = new FileOutputStream(outputFile);
fileOutputStream.write(c.getBytes());
fileOutputStream.close();
// read again from disk to make sure
Scanner scanner1 = new Scanner(new File(outputFile.getAbsolutePath()));
System.out.println(scanner1.next());
output :
varprovinfo={"cdn":"//bluehost-cdn.com","domain":"xyz.com","name":"xyz","phone":["(888)401-4678","(801)765-9400"],"code":"bh"};provinfo.cdn=location.protocol+provinfo.cdn;