I have read in a text file and am scanning said file. The question I have is how would I skip over lines that include a certain character (in my case lines that start with " // " and " " (whitespace).
Here is my code at the moment. Can someone point me in the right direction?
File dataFile = new File(filename);
Scanner scanner = new Scanner(dataFile);
while(scanner.hasNext())
{
String lineOfText = scanner.nextLine();
if (lineOfText.startsWith("//")) {
System.out.println(); // not sure what to put here
}
System.out.println(lineOfText);
}
scanner.close();
You will only want to execute the code within the while-loop if the line of text doesn't start with a / or whitespace. You can filter these out as seen below:
while(scanner.hasNext()) {
String lineOfText = scanner.nextLine();
if (lineOfText.startsWith("//") || lineOfText.startsWith(" ")) {
continue; //Exit this iteration if line starts with space or /
}
System.out.println(lineOfText);
}
As you are iterating over the lines of text in the file, use String's startsWith() method to check if the line starts with the sequences you are trying to avoid.
If it does, continue to the next line. Otherwise, print it.
while (scanner.hasNext()) {
String lineOfText = scanner.nextLine();
if (lineOfText.startsWith("//") || lineOfText.startsWith(" ") ) {
continue;
}
System.out.println(lineOfText);
}
Just use a continue like -
if (lineOfText.startsWith("//")) {
continue; //would skip the loop to next iteration from here
}
Detials - What is the "continue" keyword and how does it work in Java?
If you're just interested in printing out the lines of code that begin with a "//" then you should just use the continue keyword in java.
String lineOfText = scanner.nextLine();
if (lineOfText.startsWith("//")) {
continue;
}
See this post for more information regarding the "continue" keyword.
You can just insert "else" in your code like:
public static void main(String[] args) throws FileNotFoundException {
File dataFile = new File("testfile.txt");
Scanner scanner = new Scanner(dataFile);
while(scanner.hasNext())
{
String lineOfText = scanner.nextLine();
if (lineOfText.startsWith("//")) {
System.out.println();
}
else
System.out.println(lineOfText);
}
scanner.close();
}
}
Related
Is there any way for java.util.Scanner to include the newline escape character when reading from a file?
This is my code:
File myFile = new File("file.txt");
Scanner myReader = new Scanner(myFile);
String content = "";
while(myReader.hasNextLine()) {
content += myReader.nextLine();
}
System.out.println(content);
myReader.close();
When it reads from the file, it doesn't include '\n' or any new lines. Does anyone know how to do this?
Thanks
When it reads from the file, it doesn't include '\n' or any new lines.
Does anyone know how to do this?
You can add the new line explicitly as follows:
while(myReader.hasNextLine()) {
content += myReader.nextLine() + "\n";
}
I also recommend you use StringBuilder instead of String for appending in a loop.
StringBuilder content = new StringBuilder();
while (myReader.hasNextLine()) {
content.append(myReader.nextLine()).append(System.lineSeparator());
// or the following
// content.append(myReader.nextLine()).append('\n');
}
Check StringBuilder vs String concatenation in toString() in Java to learn more about it.
If you you just want to read in lines and the line terminator you can do it by changing the behavior of Scanner.next(). If you run the following it will take in the line and the new line terminator as one unit.
\\z is a regex directive that says to include the line terminator.
Scanner scan = new Scanner(System.in);
scan.useDelimiter("\\z");
for (int i = 0; i < 5; i++) {
String line = scan.next();
System.out.println(line + "on next line");
}
To read from a file, try this.
try {
Scanner scan = new Scanner(new File("f:/Datafile.txt"));
scan.useDelimiter("\\z");
while (scan.hasNextLine()) {
String line = scan.next();
System.out.print(line);
}
} catch (FileNotFoundException fe) {
fe.printStackTrace();
}
The scanner reads the wrong data, the text file format is:
111，Smith，Sam, 40，10.50
330，Jones，Jennifer，30，10.00
The program is:
public class P3 {
public static void main(String[] args) {
String file=args[0];
File fileName = new File(file);
try {
Scanner sc = new Scanner(fileName).useDelimiter(", ");
while (sc.hasNextLine()) {
if (sc.hasNextInt( ) ){ int id = sc.nextInt();}
String lastName = sc.next();
String firstName = sc.next();
if (sc.hasNextInt( ) ){ int hours = sc.nextInt(); }
if (sc.hasNextFloat()){ float payRate=sc.nextFloat(); }
System.out.println(firstName);
}
sc.close();
} catch(FileNotFoundException e) {
System.out.println("Can't open file "
+ fileName + " ");
}
}
}
The output is:
40，10.50
330，Jones，Jennifer，30，10.00
It is supposed to be:
Sam
Jennifer
How do I fix it?
The problem is that your data isn't just delimited by commas. It is also delimited by line-endings, and also by Unicode character U+FF0C (FULLWIDTH COMMA).
I took your code, replaced the line
Scanner sc = new Scanner(fileName).useDelimiter(", ");
with
Scanner sc = new Scanner(fileName, "UTF-8").useDelimiter(", |\r\n|\n|\uff0c");
and then ran it. It produced the output it was supposed to.
The text , |\r\n|\n|\uff0c is a regular expression that matches either:
a comma followed by a space,
a carriage-return (\r) followed by a newline (\n),
a newline on its own,
a Unicode full-width comma (\uff0c).
These are the characters we want to delimit the text by. I've specified both types of line-ending as I'm not sure which line-endings your file uses.
I've also set the scanner to use the UTF-8 encoding when reading from the file. I don't know whether that will make a difference for you, but on my system UTF-8 isn't the default encoding so I needed to specify it.
First, please swap fileName and file. Next, I suggest you use a try-with-resources. Your variables need to be at a common scope if you intend to use them. Finally, when using hasNextLine() I would then call nextLine and you can split on optional white space and comma. That could look something like
String fileName = // ...
File file = new File(fileName);
try (Scanner sc = new Scanner(file)) {
while (sc.hasNextLine()) {
String line = sc.nextLine();
String[] arr = line.split("\\s*,\\s*");
int id = Integer.parseInt(arr[0]);
String lastName = arr[1];
String firstName = arr[2];
int hours = Integer.parseInt(arr[3]);
float payRate = Float.parseFloat(arr[4]);
System.out.println(firstName);
}
} catch (FileNotFoundException e) {
System.out.println("Can't open file " + fileName + " ");
e.printStackTrace();
}
I tried to do counting lines, words, character from user "inputted" file.
After this show counting and keep asking again.
If file doesn't exist print all data which have been counted during running.
Code:
public class KeepAskingApp {
private static int lines;
private static int words;
private static int chars;
public static void main(String[] args) {
boolean done = false;
//counters
int charsCount = 0, wordsCount = 0, linesCount = 0;
Scanner in = null;
Scanner scanner = null;
while (!done) {
try {
in = new Scanner(System.in);
System.out.print("Enter a (next) file name: ");
String input = in.nextLine();
scanner = new Scanner(new File(input));
while(scanner.hasNextLine()) {
lines += linesCount++;
Scanner lineScanner = new Scanner(scanner.nextLine());
lineScanner.useDelimiter(" ");
while(lineScanner.hasNext()) {
words += wordsCount++;
chars += charsCount += lineScanner.next().length();
}
System.out.printf("# of chars: %d\n# of words: %d\n# of lines: ",
charsCount, wordsCount, charsCount);
lineScanner.close();
}
scanner.close();
in.close();
} catch (FileNotFoundException e) {
System.out.printf("All lines: %d\nAll words: %d\nAll chars: %d\n",
lines, words, chars);
System.out.println("The end");
done = true;
}
}
}
}
But I can't understand why it always show output with no parameters:
All lines: 0
All words: 0
All chars: 0
The end
Why it omits all internal part.
It may be coz I'm using few scanners, but all look ok.
Any suggestions?
UPDATE:
Thanks all who give some hint. I rethinking all constructed and rewrite code with newly info.
To awoid tricky scanner input line, I used JFileChooser:
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
import javax.swing.JFileChooser;
public class KeepAskingApp {
private static int lines;
private static int words;
private static int chars;
public static void main(String[] args) {
boolean done = false;
// counters
int charsCount = 0, wordsCount = 0, linesCount = 0;
Scanner in = null;
Scanner lineScanner = null;
File selectedFile = null;
while (!done) {
try {
try {
JFileChooser chooser = new JFileChooser();
if (chooser.showOpenDialog(null) == JFileChooser.APPROVE_OPTION) {
selectedFile = chooser.getSelectedFile();
in = new Scanner(selectedFile);
}
while (in.hasNextLine()) {
linesCount++;
lineScanner = new Scanner(in.nextLine());
lineScanner.useDelimiter(" ");
while (lineScanner.hasNext()) {
wordsCount++;
charsCount += lineScanner.next().length();
}
}
System.out.printf(
"# of chars: %d\n# of words: %d\n# of lines: %d\n",
charsCount, wordsCount, linesCount);
lineScanner.close();
lines += linesCount;
words += wordsCount;
chars += charsCount;
in.close();
} finally {
System.out.printf(
"\nAll lines: %d\nAll words: %d\nAll chars: %d\n",
lines, words, chars);
System.out.println("The end");
done = true;
}
} catch (FileNotFoundException e) {
System.out.println("Error! File not found.");
}
}
}
}
Couple of issues (actually there are many issues with your code, but I will address the ones directly related to the output you have posted):
First of all, the stuff in the catch block only happens if you get a FileNotFoundException; that's there to handle and recover from errors. I suspect you meant to put a finally block there, or you meant to do that after the catch. I suggest reading this tutorial on catching and handling exceptions, which straightforwardly describes try, catch, and finally.
Once you read that tutorial, come back to your code; you may find that you have a little bit of reorganizing to do.
Second, with the above in mind, it's obvious by the output you are seeing that you are executing the code in that catch block, which means you are getting a FileNotFoundException. This would be caused by one of two (possibly obvious) things:
The file you entered, well, wasn't found. It may not exist or it may not be where you expect. Check to make sure you are entering the correct filename and that the file actually exists.
The input string is not what you expect. Perhaps you read a blank line from previous input, etc.
Addressing reason 2: If there is already a newline on the input buffer for whatever reason, you will read a blank line with Scanner. You might want to print the value of input just before opening the file to make sure it's what you expect.
If you're seeing blank lines, just skip them. So, instead of this:
String input = in.nextLine();
scanner = new Scanner(new File(input));
Something like this instead would be immune to blank lines:
String input;
do {
input = in.nextLine().trim(); // remove stray leading/trailing whitespace
} while (input.isEmpty()); // keep asking for input if a blank line is read
scanner = new Scanner(new File(input));
And, finally, I think you can work out the reason that you're seeing 0's in your output. When you attempt to open the file with new Scanner(new File(input)); and it fails because it can't find the file, it throws an exception and the program immediately jumps to the code in your catch block. That means lines, words, and chars still have their initial value of zero (all code that modifies them was skipped).
Hope that helps.
Your println()s are in a catch block
} catch (FileNotFoundException e) {
System.out.printf("All lines: %d\nAll words: %d\nAll chars: %d\n",
lines, words, chars);
System.out.println("The end");
done = true;
}
That means you caught a FileNotFoundException. I think you can figure out from here.
private Scanner inputFile;
private String corpusFileString = "";
try
{
File file = new File(sourceFile.getText());
inputFile = new Scanner(file);
JOptionPane.showMessageDialog(null, "The file was found.");
if (text != null)
{
translate.setEnabled(true);
}
}
catch (FileNotFoundException ex)
{
JOptionPane.showMessageDialog(null, "The file was not found.");
}
try
{
numberWords = inputFile.nextInt();
}
catch (InputMismatchException ex)
{
JOptionPane.showMessageDialog(null, "The first line on the file must be an integer");
}
while (inputFile.hasNext())
{
corpusFileString = corpusFileString + inputFile.nextLine() + " ";
}
So when I read this file, the first line should be an integer(a different variable will hold that) or it will throw an exception.
The rest of the file should be data(another variable for all the data) but for some reason the String contains an empty space at the beginning and when I split it I have to use +1 in my array cause of that empty space.
The issue is that it's reading the first int, then the rest of the first line.
Basically:
15\n a line here \n another line here
Where \n is a newline.
It reads 15, then it reads to \n, which is "" (omitting the newline character). The rest it reads as you expected.
Try using:
numberWords = Integer.parseInt(inputFile.nextLine());
Instead of
numberWords = inputFile.nextInt();
Use String.Trim() to remove whitespace at the beginning and end of the string.
Link to the method: http://msdn.microsoft.com/de-de/library/t97s7bs3(v=vs.110).aspx
I am not sure about java. Possibly you have to call hasNext() before you try to read with nextInt(). This is how .NET readers and enumerators work. In c# I would write something like
while (reader.MoveNext()) {
string s = reader.Current;
}
In your case you could try
if (inputFile.hasNext()) {
numberWords = inputFile.nextInt();
}
Task: read a line from an input file. If the first word of the line is PRINT, then print the contents of the rest of the line.
Code:
else if(Data.compareTo("PRINT") == 0){
while(inFile.hasNext()){
Data = inFile.next();
System.out.print( Data + " ");
}
}
Question: How to code the scanner so that the scanner only reads one line of information at a time?
public static void ReadAndProcessPrint(File fileToRead) throws FileNotFoundException {
java.util.Scanner scanner = new Scanner(fileToRead);
while(scanner.hasNextLine()){
String line = scanner.nextLine();
if(line.startsWith("PRINT")){
String restOfLine = line.substring(5);
System.out.println(restOfLine);
}else{
//do other things
}
}
}
Hint: http://docs.oracle.com/javase/7/docs/api/java/io/BufferedReader.html
Create a InputStreamReader and using it create a BufferedReader, use readLine method.