I've not been able to resolve the following exception in the code below. What is the problem with the way I use BufferedReader? I'm using BufferedReader inside the main method
OUTPUT :-
ParseFileName.java:56: unreported exception java.io.FileNotFoundException; must be caught or declared to be thrown
BufferedReader buffread = new BufferedReader (new FileReader("file.txt"));
// ParseFileName is used to get the file name from a file path
// For eg: get - crc.v from "$ROOT/rtl/..path/crc.v"
import java.util.regex.Pattern;
import java.io.*;
public class ParseFileName {
//Split along /'s , and collect the last term.
public String getName (String longName) {
String splitAt = "/";
Pattern pattern1 = Pattern.compile(splitAt);
String[] parts = pattern1.split(longName);
System.out.println("\nparts.length = " + parts.length);
//Return the last element in the array of strings
return parts[parts.length -1];
}
public static void main(String[] args) {
ParseFileName superParse = new ParseFileName();
BufferedReader buffread = new BufferedReader (new FileReader("file.txt"));
String line;
while ((line = buffread.readLine())!= null) {
String fileName = superParse.getName(line);
System.out.println("\n" + line + " => " + fileName);
}
buffread.close();
}
}
UPDATE :
The following works:
public static void main(String[] args) throws FileNotFoundException, IOException {
However try.. catch still has some nagging issues for me:
try {
BufferedReader buffread = new BufferedReader (new FileReader("file.txt"));
} catch (FileNotFoundException ex) {
ex.printStackTrace();
} catch (IOException ex2) {
ex2.printStackTrace();
}
buffread dosent seem to get the file name. I get this error:
javac ParseFileName.java ParseFileName.java:67: cannot resolve symbol
symbol : variable buffread
location: class ParseFileName
while ((line = buffread.readLine())!= null) {
Add throws FileNotFoundException, IOException in the header of your method. It looks like just throwing the IOException will solve your problem, but incorporating both will allow you to tell if there was a problem with the file's existence or if something else went wrong (see catch statements below).
i.e.
public static void main(String[] args) throws FileNotFoundException, IOException {
Alternately, if you'd like to catch a specific exception and do something with it:
try {
BufferedReader buffread = new BufferedReader (new FileReader("file.txt"));
} catch (FileNotFoundException ex) {
// Do something with 'ex'
} catch (IOException ex2) {
// Do something with 'ex2'
}
Update to resolve the updated issue: This is just a simple scope problem which can be solved by declaring the BufferedReader outside of the try statement.
BufferedReader buffread = null;
try {
buffread = new BufferedReader (new FileReader("file.txt"));
} catch (FileNotFoundException ex) {
...
You have to add throws statement into the signature of method main or wrap code in
try {
...
} catch (FileNotFoundException e) {
...
}
Your code can throw FileNotFoundException or IOException which is Checked Exception. You need to surround your code in a try-catch block or add a throws declaration in your main function.
The BufferReader can throw an exception if the file cannot be found or opened correctly.
This error message is telling you that you need to handle this exception. You can wrap the line where you create the BufferReader in a try/catch block. This will handle the case an IOException is thrown and print out the stack trace.
public static void main(String[] args) {
ParseFileName superParse = new ParseFileName();
BufferedReader buffread;
try
{
buffread= new BufferedReader (new FileReader("file.txt"));
}
catch(FileNotFoundException e)
{
e.printStackTrace();
}
String line;
while ((line = buffread.readLine())!= null) {
String fileName = superParse.getName(line);
System.out.println("\n" + line + " => " + fileName);
}
buffread.close();
}
Another option is to add "throws IOException" to your method header.
public static void main(String[] args) throws IOException {
//...
}
This tells the compiler and callers of your method that you are choosing to not handle this exception and there is a chance it will be thrown.
Related
Would this be problematic and run into issues?
Example:
try {
File Reader fileReader = new FileReader(blah);
BufferedReader bufferedReader = new BufferedReader(fileReader);
// while-statement -- extract information from blah
try {
File Reader fileReader2 = new FileReader(blah2);
BufferedReader bufferedReader2 = new BufferedReader(fileReader2);
// while-statement -- extract information from blah2
} catch (FileNotFoundException ex) {
// Display FileNotFound stuff
} catch (IOException ex) {
// Display IOException stuff
}
} catch (FileNotFoundExcpetion ex) {
// Display FileNotFound stuff
} catch (IOException ex) {
// Display IOException stuff
}
}
If it is problematic, what other approach should I look to?
Too many try-catch would complicate code and reduce the code readability which will lead to swallowing an exception and its much more worse than performance issues as it can crash your system unexpectedly.
Here is an example of swallowing an exception and its side effects (multiple point of failures like NPE etc.).
public static void main(String[] args) {
String dataFromFile = null, dataFromDataBase = null;
try {
try {
dataFromFile = readFile();
} catch (IOException e) {
// ignore exception
// String dataFromFile will be set to null
// as there was an exception
}
// imagine many lines of code here
dataFromDataBase = readDatabase(dataFromFile.getKey());
} catch (IOException e) {
// ignore exception
}
// imagine many lines of code here
System.out.println(dataFromFile.replace(" ", ""));
//imagine many lines of code here
System.out.println(dataFromDataBase.getKey());
}
private static String readFile() throws IOException {
// throws ioexception
}
private static String readDatabase(String key) throws IOException {
// throws ioexception
}
If you are expecting multiple points in a single method that can throw exceptions then club them into one try-catch and handle them appropriately. Again there can be exception to this specific question but you should always try to reduce multiple try-catch in single method.
Unless you are doing something specific with an exception, use single Exception clause to handle all exception and log details or throw it to the caller to handle it in its own specific ways.
try {
File Reader fileReader = new FileReader(blah);
BufferedReader bufferedReader = new BufferedReader(fileReader);
// while-statement -- extract information from blah
File Reader fileReader2 = new FileReader(blah2);
BufferedReader bufferedReader2 = new BufferedReader(fileReader2);
// while-statement -- extract information from blah2
} catch (Exception ex) {
// Display Exception stuff details
}
}
In this example I see no reason to start a new try statement. why not do this?
try {
File Reader fileReader = new FileReader(blah);
BufferedReader bufferedReader = new BufferedReader(fileReader);
File Reader fileReader2 = new FileReader(blah2);
BufferedReader bufferedReader2 = new BufferedReader(fileReader2);
} catch (FileNotFoundExcpetion ex) {
// Display FileNotFound stuff
} catch (IOException ex) {
// Display IOException stuff
}
But no, there would be no problem. it just looks bad. but sometimes needed I guess.
I need to read a txt file and store my data to a treeSet.
public class UrbanPopulationStatistics {
private Set<UrbanPopulation> popSet;
private File file;
private BufferedReader br;
public UrbanPopulationStatistics(String fileName) throws IOException {
this.popSet = new TreeSet<>();
readFile("population.txt");
}
private void readFile(String fileName) throws IOException {
try {
br = new BufferedReader(new FileReader(fileName));
String line;
while ((line=br.readLine()) != null) {
String[] array = line.split("/");
popSet.add(new UrbanPopulation(array[0], Integer.parseInt(array[1]), Integer.parseInt(array[4])));
}
} catch (IOException e) {
e.printStackTrace();
}
br.close();
}
#Override
public String toString() {
String s = popSet.toString().replaceAll(", ", "");
return "UrbanPopulationStatistics:\n" + s.substring(1, s.length() - 1) + "\n";
}
public static void main(String[] args) throws IOException {
UrbanPopulationStatistics stats = new UrbanPopulationStatistics("population.txt");
System.out.println(stats);
}
}
I have tried to turn what the buffered reader reads into an array and then add it into my treeSet, but I get the error: Exception in thread "main" java.lang.UnsupportedOperationException: Not supported yet.
You have an extra period after parseInt at Integer.parseInt.(array[4])));.
Be careful when writing code. Syntax errors don't show up "nicely", i.e. the error message is not very helpful in most cases. It does show you the approximate location of the error though.
The problem with your code is you are not storing what you read from the buffer (and hence reading twice from the buffer). You need to assign what you read in a variable to check for null as below:
private void readFile(String fileName) throws IOException {
try {
br = new BufferedReader(new FileReader(fileName));
String line = null;
while ((line = br.readLine()) != null) {
String[] array = line.split("/");
popSet.add(new UrbanPopulation(array[0], Integer.parseInt(array[1]), Integer.parseInt(array[4])));
}
} catch (IOException e) {
e.printStackTrace();
} finally {
br.close();
}
}
Also I would close the BufferedReader in the finally block to avoid resource leaks.
I tried to reproduce the error using your code, but it doesn't happened. Your code is ok.
UnsupportedOperationException are exceptions that can happen when you try to add an element in a collection.
But TreeSet implements the add method.
I work in BlueJ in Windows. I tried to read a character in Java using the following method:
import java.util.Scanner;
import java.io.*;
public class Test{
public static void main(String args[]) {
InputStreamReader instream = new InputStreamReader (System.in);
BufferedReader stdin = new BufferedReader(instream);
char c = (char) stdin.read();
}
}
When I compiled it, the compiler gave an error:
Unreported exception java.io.IOException; must be caught or declared
I did not understand the problem. Can anyone suggest me a way to do it properly.
The line stdin.read() could throw an IOException which is what the error message is telling you. You need to handle this by either declaring that your main method will throw it:
public static void main(String args[]) throws IOException {
// ...
}
or by handling the IOException inside main by using a try/catch like this:
public static void main(String args[]) {
try {
InputStreamReader instream = new InputStreamReader (System.in);
BufferedReader stdin = new BufferedReader(instream);
char c = (char) stdin.read();
} catch (IOException ex) {
// handle error in some way
ex.printStackTrace();
}
}
Use try catch block to handle IOException in your code. you can do this.
import java.util.Scanner;
import java.io.*;
public class Test {
public static void main(String args[]) {
try {
InputStreamReader instream = new InputStreamReader(System.in);
BufferedReader stdin = new BufferedReader(instream);
char c = (char) stdin.read();
} catch (IOException ex) {
System.out.println("Error : " + ex.getMessage());
}
}
}
Catch the exception.
public static void main(String args[]) {
try{
InputStreamReader instream = new InputStreamReader (System.in);
BufferedReader stdin = new BufferedReader(instream);
char c = (char) stdin.read();
}catch(IOException ioe){
ioe.printStackTrace();
// write your handling
}catch(Exception err){
err.printStackTrace();
}
}
// You can catch relevant multiple exceptions using catch block. If you are not sure of specific exception, catch generic Exception. All sub classes of Exception should be handled first and generic Exception should be caught in the last.
Could you help me understand where should I throw exceptions and catch them.
Please, have a look at my code. I thought that in Thrd class I have already thrown and caught the exception. But when I wrote in the main class FirstThread.readFile("ParallelProgramming.txt");, I faced a runtime error - unhandled exception. So, I had to use try and catch. So, I somehow can't understand why in the Thd class my try and catch blocks didn't work.
package parallelprogramming;
import java.lang.Thread;
import java.io.*;
public class Thrd extends Thread {
public void readFile(String File) throws FileNotFoundException {
FileReader fr = new FileReader(File);
BufferedReader br = new BufferedReader(fr);
String s;
try {
while ((s = br.readLine()) != null) {
System.out.println(s);
}
fr.close();
}
catch (FileNotFoundException FNFD) {
System.out.println("File not found!");
}
catch (IOException IOE){
System.out.println("IOException caught!");
}
}
}
package parallelprogramming;
import java.io.FileNotFoundException;
public class ParallelProgramming {
public static void main(String[] args) throws FileNotFoundException {
Thrd FirstThread = new Thrd();
try {
FirstThread.readFile("ParallelProgramming.txt");
} catch (FileNotFoundException FNFD) {
System.out.println("File not found!");
}
}
}
The rules with checked exceptions (and this includes IOException, which FileNotFoundException is a child of), are as follows:
if you cannot, or do not want, to handle it in your current method, declare that the method throws it;
if you want to handle it in your current method, then catch it; note that even in this case you can rethrow that exception;
if main() throws any exception, and this exception triggers, the program terminates.
Now, we suppose that you are using Java 7. In this case, do that:
public void readFile(final String file)
throws IOException
{
final Path path = Paths.get(file);
for (final String line: Files.readAllLines(path, StandardCharsets.UTF_8))
System.out.println(line);
}
Why bother? ;)
If you don't want to do that but read line by line, then:
public void readFile(final String file)
throws IOException
{
final Path path = Paths.get(file);
try (
final BufferedReader reader = Files.newBufferedReader(path,
StandardCharsets.UTF_8);
) {
String line;
while ((line = reader.readLine()) != null)
System.out.println(line);
}
}
The second form is preferred if you wish to treat exceptions specifically. Note that with Java 7, you have meaningful exceptions as to why you cannot access the file vs IOException: NoSuchFileException, AccessDeniedException, etc etc. All these inherit FileSystemException. The old file API can't do that for you.
This means that if you want to deal with filesystem level errors you can do:
catch (FileSystemException e) { /* ... */ }
where before that you did:
catch (FileNotFoundException e) { /* ... */ }
Translated to the code above, if you want to catch exceptions you'll then do:
// All exceptions handled within the method -- except if you rethrow it
public void readFile(final String file)
{
final Path path = Paths.get(file);
try (
final BufferedReader reader = Files.newBufferedReader(path,
StandardCharsets.UTF_8);
) {
String line;
while ((line = reader.readLine()) != null)
System.out.println(line);
} catch (FileSystemException e) {
// deal with a filesystem-level error
// Note that you MUSt catch it before IOException
// since FileSystemException inherits IOException
} catch (IOException e) {
// deal with a low-level I/O error
}
}
Remove 'throws FileNotFoundException' from the readFile method of class Thrd then you dont need to handle this exception in main method of class ParallelProgramming.
As you throw FileNotFoundException from readFile method then exception will pass to the method will called this i.e. then main method need to handle this exception.
There are two ways to handle an exception either you need to catch it or throw it again.
In the readFile method you have done both. you caught the exceptions using catch blocks then you have mentioned that readFile method throws FileNotFoundException, so when ever you use readFile method you need to catch the exception again.
This program is compiling though not working. It just handling the opening file exception. Please help me.Thanks for your time.
import java.io.*;
import java.util.Scanner;
public class ReadingFile {
/**
* #param args
*/
public static void main(String[] args) {
ReadingFile rf = new ReadingFile();
rf.printOnScr();
}
private BufferedReader openFile(String meString){
Scanner sc = new Scanner(System.in);
BufferedReader bf = null;
while (bf == null) {
try {
System.out.println("Enter a file name");
String fileName = sc.nextLine();
FileReader b = new FileReader(fileName);
bf = new BufferedReader(b);
} catch (IOException e) {
System.out.println("The file you are trying to open dose not exist.");
}
}
return bf;
}
private void printOnScr() {
BufferedReader br = openFile("Please enter a file");
try {
while(true){
String line = br.readLine();
if(line == null) break;
System.out.println(line);
}
br.close();
} catch (IOException e) {
System.out.println("The line you are trying to access have problem/s");
}
}
}
Very probably you're not specifying the correct path to the file when you type it. It should either be an absolute path or a relative path based at your current working directory. To see exactly what's happening, though, you'll need to look at the exception that's thrown. Either print it out with
e.printStackTrace()
or wrap it in an unchecked exception:
throw new IllegalStateException(e);
or let IOException be thrown from openFile(), through printOnScr(), and out of main()