I am a new java student currently working on File I/O. My professor has asked us to create a very simple "DC universe" game using interfaces and classes and has asked us in the current lab I am working on, to create an instance of an object and then save the file to a directory in our C drive. My problem, is that even after all my constant 2 hours of digging through past topics I still cannot find a proper explanation as to how I create a directory and THEN create a file and write to a file in that directory because it appears whenever I run my code to not be able to do both tasks simultaneously. The code below also contains an error at the "Print Writer" line and asks to add a throw clause for "file not found exception"
Any and all help is vastly appreciated
package runtime;
import java.io.*;
import java.util.*;
import model.hero.*;
public class Gameplay {
public static void main(String[] args) {
File x = new File("C://prog24178//dcheroes.dat");
if(!x.exists()){
x.mkdir();
}
PrintWriter output = new PrintWriter(x);
// 1. Create a save file called dcheroes.dat in {$root}\prog24178
// 2. Create a hero
// 3. Save hero to file
}
}
Two errors I see:
x.mkdir() will try to create C:\prog24178\dcheroes.dat as a directory. Use x.getParent().mkdir() to create C:\prog24178.
the PrintWriter error is Java complaining about you not catching a potential error. Your code is fine, it's just Java being demanding. Surround your code with a try { ... } catch (FileNotFoundException ex) { ... } block. Every function call that could potentionally throw an Exception needs to have that exception caught, or the containing function needs to be marked to also be a potential source of the exception (and you can't do the latter on main).
Related
I'm trying to write a parser to a file called "x". I want to use scanner. I tryied to follow actions from a tutorial: https://www.youtube.com/watch?v=3RNYUKxAgmw.
package q;
import java.io.File;
import java.util.Scanner;
public class Parser {
public static void main(String [] args) {
Scanner x = new Scanner(new File("/home/x/eclipse-workspace/q/src/q/x.txt"));
String s=x.nextLine();
System.out.print(s);
}
}
The file that I want to open is called "x", its text file. We can see it in Package Explorer on left side. I clicked right on its properties. There is visible file locatization.
There appears FileNotFoundException as on the picture. I doesn't understand why this file cannot be opened.
[update] But I'm not sure if this is what
There appears FileNotFoundException as on the picture. I doesn't
understand why this file cannot be opened.
That's not what's happening. The error is in compilation time (the program has not executed, it doesn't know if the file -will- exist). The compiler is telling you "this method/constructor, according to its declaration, can throw an Exception (in this case: a FileNotFoundException ) at run time; you have not told me what to do in that case".
You really need to read about how Exceptions are treated in Java.
For a quick remedy, add a throws Exception to your main declaration. (Bear in mind: that is an awful thing to do if you don't really understand what are you doing)
Before I start, I'd like to say that I've spent 4 hours today, 6 hours yesterday and 3 hours before that researching this issue. I've read every post I can find, followed every instruction to the letter, restarted my project, reinstalled my IDE (Netbeans) and even fresh installed my OS, and I haven't found a single piece of helpful advice, so I figured I needed to ask for help.
AND YES, I HAVE PUT THE FILE IN THE RIGHT LOCATION
... As a matter of fact, I've put the file in EVERY location. There's a copy in every folder inside my project and also a copy in the overall Projects folder, and also in My Documents. I've checked and changed and defaulted the root directory many times. PLEASE don't tell me to just use an exception handler. The file the program reads in is guaranteed to exist and contain something.
So here's my question:
I'm trying to input and read from a file, however, the result is always that the file can't be found. Here's an example of my code (and it really is down to this atm):
package project2;
import java.io.FileReader;
import java.io.*;
import java.util.Scanner;
public class Project2 {
public static void main(String[] args) {
FileReader inputFile = new FileReader(args[0]);
}
}
Here are two of the errors I get (I also get Filenotfound errors, but I don't think I need to add that):
Exception in thread "main" java.lang.RuntimeException: Uncompilable source
code - unreported exception java.io.FileNotFoundException; must be caught or
declared to be thrown
at project2.Project2.main(Project2.java:14)
C:\Users\jarre\AppData\Local\NetBeans\Cache\8.2\executor-snippets\run.xml:53:
Java returned: 1
BUILD FAILED (total time: 1 second)
Exception in thread "main" java.util.NoSuchElementException: No line found
at java.util.Scanner.nextLine(Scanner.java:1540)
at project2.Project2.main(Project2.java:24)
C:\Users\jarre\AppData\Local\NetBeans\Cache\8.2\executor-snippets\run.xml:53:
Java returned: 1
BUILD FAILED (total time: 0 seconds)
That's it. The file name comes from the arguments, and I have tried every possible variation of the name. I have tried naming the file outside of the arguments, as just the file name itself and also with an explicit file path.
Using a scanner won't let me read anything in. FileReader won't even run.
The text file has no special formatting or characters, and I've used the one I was supplied with and multiple that I hand typed just in case there was an issue with the one I was given. I have also made sure that ".txt" is never read or used twice (I keep my extensions on, anyway).
I have checked attributes and permissions of all files and the Netbeans program itself. I've also made sure that the text files were included in the project build.
I am not using any additional code right now, as I can't do anything until I'm sure that I can read in a file, and then output one as well. I also know that the text files aren't corrupt because I can read them in Python just fine, however, I have to use Java and I have to use Netbeans.
This is a new problem for me, I've always been able to read in files fine, and I've exhausted my options. I really need some help if anyone has any ideas.
The first exception (java.lang.RuntimeException: Uncompilable source
code) is thrown because the code that you have shown us is not valid java source code.
new FileReader(args[0]) is declared as throwing FileNotFoundException and according to the rules of the java language you either have to catch this exception or declare your main method as throwing this exception.
One way to fix this problem is to write your main method like this:
public static void main(String[] args) throws FileNotFoundException {
FileReader inputFile = new FileReader(args[0]);
}
It seems that you have solved this issue because the second exception (java.util.NoSuchElementException: No line found) is thrown by the Scanner.nextLine() method if you try to read past the end of the file.
Since you have not shown any code using the Scanner class it's hard to tell where to problem is in this case.
As a matter of fact, I've put the file in EVERY location. There's a copy in every folder inside my project and also a copy in the overall Projects folder, and also in My Documents.
Don't do that. You are creating a mess with files that will be hard to cleanup. If you want to know which file your program is reading then adding the following simple line tells you the exact path and filename:
System.out.println(new File(args[0]).getAbsolutePath());
Have you ever tried with a simple, minimal example like this:
package project2;
import java.io.FileReader;
import java.io.*;
import java.util.Scanner;
public class Project2 {
public static void main(String[] args) {
System.out.println(new File(args[0]).getAbsolutePath());
FileReader inputFile = new FileReader(args[0]);
try (Scanner s = new Scanner(inputFile)) {
while (s.hasNextLine()) {
System.out.println(s.nextLine());
}
}
}
}
It should print out the name of your file with the complete path and then the contents of the file line by line.
I don't think Java is messing around with you a not found file is a not found file, please elaborate more in this issue by screens of files and directories you are working on.
I would like you to consider take a look at the following:
FileReader
Path of projects on Netbeans
I hope this helps may the code be with you.
This reads a file with no problem. I'll assume you're running JDK 8.
/**
* Read a file example
* User: mduffy
* Date: 4/21/2017
* Time: 7:48 AM
* #link http://stackoverflow.com/questions/43529600/java-nothing-will-read-in-this-file
*/
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
public class Project2 {
public static void main(String[] args) {
if (args.length > 0) {
BufferedReader reader = null;
try (BufferedReader bufferedReader = new BufferedReader(new FileReader(args[0]))) {
bufferedReader.lines().forEach(System.out::println);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
} else {
System.out.println("Usage: Project2 <file>");
}
}
}
Here's the input file I used:
line1
line2
hello, michael
line 4
Here's the output I got:
java Project2 .\src\main\resources\test.txt
line1
line2
hello, michael
line 4
Process finished with exit code 0
When I run the below code, I get the error that Could not find or load main class. I have removed the package and created it again. But the error is still exist. I did some methods to fix it such as right clicking on package name -> properties -> run option to change the main method but there is nothing. But if I create another package name and write this code in it, the program work.
package craps;
public class Craps {
public static void main(String[] args) {
int number = 10;
System.out.println(number);
}
}
Your code is not having any errors
I don't know what is happening in Netbeans .I have been using this for years and living with this kind of errors.
perhaps you get this when netbeans running out of memory and that particular moment you are editing this file.
My workaround for this kind of errors are
1.Do some dummy editing in that file like commenting some empty line // and save All and recompile it
2.Close and open this project (Sometimes work)
Following code opens status very fine in notepad:
import java.util.*;
class test
{
public static void main(String args[])
{
try{
ProcessBuilder pb=new ProcessBuilder("notepad","F:/status");
pb.start();
}catch(Exception e)
{
System.out.println(e);
}
}
}
Following code does'not play the song:
import java.util.*;
class test
{
public static void main(String args[])
{
try{
ProcessBuilder pb=new ProcessBuilder("C:/Program Files (x86)/VideoLAN/VLC/vlc","D:/02 Tu Jaane Na");
pb.start();
}catch(Exception e)
{
System.out.println(e);
}
}
}
I think that the problem is that you're ignoring the fact that the files you're trying to open have filename extensions.
Windows Explorer doesn't display file extensions by default - that is probably why you are not aware of their existence.
The reason why notepad worked in your first example is that notepad automatically adds .txt extension to its filename parameter in case you didn't provide one yourself. So in reality the file that is being open is not status but status.txt.
VLC doesn't have this "advanced" functionality because there's no specific filename extension it is designed to work with.
So you will need to look up the dir command output and add the full file name as a parameter.
If that was the real issue - you might want to modify your Windows Explorer settings for it to display file extensions:
or, which is better, switch to a more programmer-friendly OS :)
For 1.6+ code, use Desktop.open(File) instead.
Of course, the sensible thing to do immediately before calling that is to check File.exists().
OTOH, Desktop.open(File) throws a slew of handy exceptions, including:
NullPointerException - if file is null
IllegalArgumentException - if the specified file doesn't exist
UnsupportedOperationException - if the current platform does not support the Desktop.Action.OPEN action
IOException - if the specified file has no associated application or the associated application fails to be launched
Properly handled, the exception would indicate the immediate problem.
As an aside, the Desktop class is designed to be cross-platform, and will handle any file type for which an association is defined. In that sense it is a lot more useful for something like this, than trying to use a Process.
I am currently putting a program into a .jar, and have difficulties telling it where to get its data from. The data was inside of a file in the project, and I am sure that it is located in the jar as well. But I have no clue on how to get a path into a jar.
I found the getClass().getClassLoader().getResourceAsStream() method online to get an input stream into the jar, but since I used FileReaders all the time, I dont know what to do with it as well..
I`d be very thankful for any help.
Edit:
Here is a picture of how the directory is organized:
My command window shows what happens if I run the .jar. Nullpointer in line 30. I tried it with and without .getClassLoader(), it just wont find it.
Here is the inside of the jar:
again, app is where the class files are in. Hence, via class.getResource.. I should be able to search in DataPackeg. Man, this is wearing me out.
A key concept to understand is that files don't exist inside of jars. You must instead get your data as a read-only resource, and you will need to use a path that is relative to path of your class files.
If you're still stuck, you may need to tell us more specifics about your current program, its structure, what type of data you're trying to get, where it's located in the jar file, and how you're trying to use it.
For instance, say your package structure looked like this:
So the class file is located in the codePackage package (this is Eclipse so the class files live in a universe parallel to the java files), and the resource's location is in the codePackage.images package, but relative to the class file it is the images directory, you could use the resource like so:
package codePackage;
import java.awt.image.*;
import java.io.*;
import javax.imageio.*;
import javax.swing.*;
public class ClassUsesResources {
private JLabel label = new JLabel();
public ClassUsesResources() {
try {
BufferedImage img = ImageIO.read(getClass().getResourceAsStream(
"images/img001s.jpg"));
ImageIcon icon = new ImageIcon(img);
label.setIcon(icon);
JOptionPane.showMessageDialog(null, label);
} catch (IOException e) {
e.printStackTrace();
System.exit(-1);
}
}
public static void main(String[] args) {
new ClassUsesResources();
}
}