It's not showing any error but the content should be saved to my file, which is not saving...
import java.util.Scanner;
import java.io.*;
import java.util.logging.Level;
import java.util.logging.Logger;
public class FileReadLine {
public static void main(String[] args) {
try {
String str;
Scanner sc=new Scanner(System.in);
do {
System.out.println("Enter your lines");
str=sc.nextLine();
FileWriter fw = new FileWriter("C:/test/abcd.txt");
if(!str.equals("stop"))
fw.write(str);
fw.write("\n");
fw.close();
} while(!str.equals("stop"));
} catch (Exception ex) {
System.out.println(ex);
}
}
}
please correct my code if i am wrong
You are trying to create a new file inside the loop. So it gets overridden. Change the program to create the file once(before loop) and use it inside the loop to write it.
Also do not close the file as soon as you have written it. Use it once you encounter "stop". Close() should be used when you are done with writing into the file.
Try using flush() before close() to send all data in the buffer to the the file.
You must close you FileWriter (fw) out of while loop.
Try below code
public static void main(String[] args) throws IOException {
FileWriter fw = null;
try {
fw = new FileWriter("C:/Users/MYPC/Desktop/abcd.txt");
String str;
Scanner sc = new Scanner(System.in);
do {
System.out.println("Enter your lines");
str = sc.nextLine();
if (!str.equals("stop")){
fw.write(str);
}
fw.write("\n");
} while (!str.equals("stop"));
} catch (Exception ex) {
System.out.println(ex);
// Logger.getLogger(FileReadLine.class.getName()).log(Level.SEVERE,
// null, ex);
}finally{
if(fw != null){
fw.close();
}
}
}
You were closing the writer in every iteration since you are not using braces in the if condition...
Try this solution, is working
try {
String str;
Scanner sc=new Scanner(System.in);
File fw = new File("C:/Users/MYPC/Desktop/abcd.txt");
FileOutputStream fos = new FileOutputStream(fw);
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(fos));
do {
System.out.println("Enter your lines");
str=sc.nextLine();
if(!str.equals("stop")) {
bw.write(str);
bw.newLine();
} else {
bw.close();
}
} while(!str.equals("stop"));
} catch (Exception ex) {
System.out.println(ex);
}
Related
I have the below piece of code.
import java.io.*;
public class FileTest {
public static void main(String[] args) throws IOException {
WriteLinesToFile("miss.txt","This is a special file");
}
public static void WriteLinesToFile(String outputFileName, String lineConverted) throws IOException {
File f = new File(outputFileName);
if (f.createNewFile()) {
System.out.println("File is created!");
FileWriter writer = new FileWriter(f);
writer.write(lineConverted);
writer.close();
} else {
System.out.println("File already exists.");
FileWriter writer = new FileWriter(f);
writer.write(lineConverted);
writer.close();
}
}
}
I need the same logic, without throwing exception. Could someone tell me how to do this?
You could handle your exception with a try{} catch(IOException e){}
But it's important to handle the exception, because otherwise your program will do something, but not what you want.
import java.io.*;
public class FileTest {
public static void main(String[] args)
{
writeLinesToFile("miss.txt", "This is a special file");
}
public static void writeLinesToFile(String outputFileName, String lineConverted){
File f = new File(outputFileName);
try {
if (f.createNewFile()) {
System.out.println("File is created!");
FileWriter writer = new FileWriter(f);
writer.write(lineConverted);
writer.close();
} else {
System.out.println("File already exists.");
FileWriter writer = new FileWriter(f);
writer.write(lineConverted);
writer.close();
}
}
catch(IOException e){
//Handle your error
}
}}
But you can't cut out the exceptions at all, because handling files in java throws always exceptions (For example if the file could not be found).
In the output file "CMFTSwitchesnew.txt" only has the last line of the input file. I've tested a few different methods such as changing write.println(input.nextLine()) but I'm not sure now where the issue is.
package WorkingWithFiles;
import java.io.*;
import java.util.Scanner;
public class FileIO
{
public static void main(String[] args)
{
File output = new File("CMFTSwitchesNew.txt");
File source = new File("src/CMFTSwitches.txt");
try {
Scanner input = new Scanner(source);
while (input.hasNextLine()) {
try {
PrintWriter write = new PrintWriter(output);
String text = input.nextLine();
write.println(text) // also tried
// write.println(input.nextLine());
write.close();
} catch (Exception e) {
System.out.println("Exception found");
}
}
} catch (FileNotFoundException e) {
System.out.println("The file was not found");
}
}
}
try {
PrintWriter write = new PrintWriter(output);
String text = input.nextLine();
write.println(text) // also tried
// write.println(input.nextLine());
write.close();
} catch (Exception e) {
System.out.println("Exception found");
}
You're creating a PrintWriter in each iteration without using the constructor that allows you to tell the PrintWriter to append data at the end of an already existing file. That way you only see the output of the last time the file was written. Either change that to
PrintWriter write = new PrintWriter(output, true);
or instantiate the PrintWriter outside the while-loop and close it after it.
These are the contents of the constructor of a class which is called by the main method.
File f = null;
Scanner s;
try {
f = new File(getClass().getResource("/LOL.txt").toURI());
} catch (URISyntaxException e) {
e.printStackTrace();
}
try {
s = new Scanner(f);
while(s.hasNextLine()) System.out.println(s.nextLine());
} catch (FileNotFoundException e) {
e.printStackTrace();
}
try {
FileWriter fw = new FileWriter(f.getAbsoluteFile(), false);
BufferedWriter bw = new BufferedWriter(fw);
bw.write("LOL");
bw.close();
} catch (IOException e) {
e.printStackTrace();
}
Output in the console:
LOL
The contents of the file remain unchanged even after repeated runs. My IDE is eclipse
You parametrize your FileWriter with boolean append set as false.
Therefore, the same file will be written over every time that given constructor is executed, and "LOL" will be printed in it.
Before printing "LOL", a Scanner reads each line and prints it, hence the LOL printed in our system out.
Also note, you probably want to declare your FileWriter and BufferedWriter out of the try block, so you can flush and close them in a finally block.
This post only contains the initial question, as-is with everything corrected to avoid several resource-related bugs. It assumes Java 6 or lower.
I shouldn't get any upvote so please don't ;)
package so39452286;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.Writer;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
new Main().run();
}
public void run() {
try {
File file = new File(getClass().getResource("/LOL.txt").toURI());
Scanner scanner = null;
try {
scanner = new Scanner(file);
while (scanner.hasNextLine()) {
System.out.println(scanner.nextLine());
}
} finally {
if (scanner != null) {
scanner.close();
}
}
Writer writer = null; // Holds the main resource, not the wrapping ones.
try {
writer = new FileWriter(file.getAbsolutePath(), false);
BufferedWriter bw = new BufferedWriter(writer);
bw.write("LOL");
bw.flush(); // You forgot to flush. Ok, close() does it, but it's always better to be explicit about it.
} finally {
if (writer != null) {
writer.close();
}
}
} catch (Exception e) {
// Do something with e.
e.printStackTrace(System.err);
}
}
}
course.txt file is not read by my code. It allows me to enter the file name, but doesn't open the file.
package javaexam;
import java.io.*;
import java.util.ArrayList;
import java.util.HashMap;
import java.io.BufferedReader;
import java.util.Scanner;
public class BufferReader {
public static void main(String[] args) {
Scanner scanner=new Scanner(System.in);
BufferedReader bf = null; // shows warning that assigned but never used
String line;
System.out.println("Please enter the file name");
try {
bf = new BufferedReader(new FileReader("C:\\Users\\MohammedArfa\\Desktop\\New folder\\" + scanner.next()));
} catch(FileNotFoundException fnfex) {
//shows warning that the buffer assignment is declared but never used
System.out.println(fnfex.getMessage()+"The file was not found");
}
System.exit(0);
try {
while((line=bf.readLine()) != null) {
System.out.println(line);
}
} catch(IOException ex) {
System.out.println(ex.getMessage()+"Error reading file");
} finally {
System.out.println(0);
}
}
}
Move the system.exit(0) into the catch statement above...
try {
bf = new BufferedReader(new FileReader("C:\\Users\\MohammedArfa\\Desktop\\New folder\\" + scanner.next()));
} catch(FileNotFoundException fnfex) {
//shows warning that the buffer assignment is declared but never used
System.out.println(fnfex.getMessage()+"The file was not found");
System.exit(0);
}
If the system.exit(0) is not inside the catch then it is always being executed which terminates your program before you reach the print out loop.
How do I use FileWriter to actually write into a file and then open it on notepad and see what I wrote? This is what I tried so far:
package Experimental;
import java.io.*;
public class IO {
public static void main (String args[]) {
File f = new File("testFile.txt");
//Outputting into a file
try {
PrintWriter filePrint = new PrintWriter(
new BufferedWriter(new FileWriter(f,true))
);
filePrint.println("testing, testing, printing into a file (apparently)");
} catch (IOException e) {
System.out.println(e.getMessage());
}
}
}
Don't forget to close your FileWriter once you are done writing to it.
You should flush and close the PrintWriter like this:
File file = new File("testFile.txt");
PrintWriter filePrint = new PrintWriter(new BufferedWriter(new FileWriter(file, true)));
try
{
try
{
filePrint.println("testing, testing, printing into a file (apparently)");
filePrint.flush();
}
finally
{
filePrint.close();
}
}
catch (IOException e)
{
e.printStackTrace();
}