I am in a Linux Envirnomnet. I am also using Netbeans. Here is my code below:
import java.io.*;
public class myFirstJavaProgram {
public static void main(String[] args) {
File file = new File("home/gk/Hello1.txt");
// creates the file
file.createNewFile();
// creates a FileWriter Object
}
}
You forgot a slash before home. It is looking for a folder that most likely does not exist inside the classpath.
EDIT
After you pointed out the exception you were receiving I realized that a checked exception is not being handled. You need to catch the possible IOException or include the exception in the method signature.
import java.io.*;
/**
*
* #author Ashwin Parmar
*/
public class myFirstJavaProgram {
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
try {
File file = new File("/home/gk/Hello1.txt");
file.createNewFile();
} catch(IOException e) {
System.out.println(e.getMessage());
}
// creates a FileWriter Object
}
}
When dealing with any File IO action in Java, it is always best to use a try/catch loop
Error in your path.
This home/gk/Hello1.txt should be /home/gk/Hello1.txt
Related
I'm using Java to create a program that takes in a CSV file and outputs an Arff file. Whenever the program runs it comes up catching the exception that No source has been specified. When I delete the try catch it comes with the following error and I am not sure why,
Exception in thread "main" java.io.IOException: No source has been specified
at weka.core.converters.CSVLoader.getDataSet(CSVLoader.java:867)
at CSVtoArff.Convert(CSVtoArff.java:10)
at CSVtoArff.main(CSVtoArff.java:23)
Below is the code for the program
import weka.core.Instances;
import weka.core.converters.CSVLoader;
import weka.core.converters.ArffSaver;
import java.io.File;
public class CSVtoArff {
public static void Convert(String input, String output) throws Exception {
try {
CSVLoader load = new CSVLoader();
load.setSource(new File(input));
Instances data = load.getDataSet();
ArffSaver save = new ArffSaver();
save.setInstances(data);
save.setFile(new File(output));
save.writeBatch();
System.out.println("File successfully converted");
}
catch (Exception e) {
System.out.println("Does not meet arff standards: " + e.getMessage());
}
}
public static void main(String[] args) throws Exception{
String input = "C:\\Users\\jason\\Desktop\\example.csv";
String output =" C:\\Users\\jason\\Desktop\\example.arff";
Convert(input, output);
}
}
Please try putting the files in C:\temp folder and change it to below and try.
Sometime windows security my be denying access to protected system folders.
Also there is an extra leading space in output file path. I have removed that.
public static void main(String[] args) throws Exception{
String input = "C:/temp/example.csv";
String output ="C:/temp/example.arff";
Convert(input, output);
}
I have two classes in a Maven project, which contain the same code (except for their name). The code shall later create a new class with Javassist based on a csv-file.
The first one CsvParser is placed in the src/main/java/csvParser package. The second one TestCsvParser is placed in the src/test/java/csvParser package. In both packages the same file assistant.csv is placed.
When I run the one from the main directory (CsvParser) I get a java.lang.NullPointerException but when I run TestCsvParser, placed in the testdirectory the same code works fine.
Why is it like that? (Or do I just not see something? ;) )
CsvParser:
package csvParser;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class CsvParser {
public static void main(String[] args) throws IOException
{
createClass("/assistant.csv");
}
/**
* Create a class from a csv-file.
*/
private static void createClass(String input) throws IOException {
try(BufferedReader stream = new BufferedReader(new InputStreamReader(
CsvParser.class.getResourceAsStream(input))))
{
// Create class based on csv-file.
}
}
}
TestCsvParser:
package csvParser;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class TestCsvParser {
public static void main(String[] args) throws IOException
{
createClass("/assistant.csv");
}
/**
* Create a class from a csv-file.
*/
private static void createClass(String input) throws IOException {
try(BufferedReader stream = new BufferedReader(new InputStreamReader(
TestCsvParser.class.getResourceAsStream(input))))
{
// Create class based on csv-file.
}
}
}
The exception
Exception in thread "main" java.lang.NullPointerException
at java.io.Reader.<init>(Reader.java:78)
at java.io.InputStreamReader.<init>(InputStreamReader.java:72)
at csvParser.CsvParser.createClass(CsvParser.java:19)
at csvParser.CsvParser.main(CsvParser.java:11)
I believe this question is not a duplicate of a question like What is a NullPointerException because:
The NullPointerException occurs based on the location of the class and the resource referred to. So it's more about directory structures and Mavens targetdirectory.
Thanks for your time!
Finally I found the error. I added the assistant.csv beside the two classes (CsvParser and TestCsvParser). But in both cases this file is not added to the target directory.
The reason why it was working in TestCsvParser is an additional assistant.csv in the ../test/resource/ directory. In fact the two conditions which I described missed this fact and therefore you could not reconstruct my error fully. I'm sorry for that.
To have a working example the resource files both for main and test have to placed within the resource folder instead of beside the class.
Thanks for your help, especially Kalaiselvan A.
It will depend on location of "/assistant.csv" file and if it's not found, you will get NPE. The path will be dependent on your class location since you are calling CsvParser.class.getResourceAsStream..
I ran the below code and created a file. Where can I find it in my filesystem?
import java.io.*;
public class FileReaderDemo {
public static void main(String args[]) throws Exception {
File f = new File ("wayback.txt");
f.createNewFile();
System.out.println(f.exists());
}
}
Add the following to your program, run it and it'll show you the expected location:
System.out.println(f.getCanonicalFile());
Lets say I'm working in a very large project, and have noticed an empty print line, so I'm assuming there is a System.out.println(""); located somewhere in the code. How would I go about trying to figure out where it is, short of just searching the entire project for all occurrences of System.out.println?
If you're using Java 8+, Durian has a StackDumper class which makes it easy to find where a given line is being printed:
StackDumper.dumpWhenSysOutContains("SomeTrigger")
When "SomeTrigger" is printed, this will get dumped to System.err:
+----------\
| Triggered by SomeTrigger
| at package.MyClass.myMethod(MyClass.java:62)
| (the rest of the stacktrace)
+----------/
For your case (looking for an empty string), it's a little more complicated:
PrintStream sysOutClean = System.out;
StringPrinter sysOutReplacement = new StringPrinter(StringPrinter.stringsToLines(line -> {
if (line.isEmpty()) {
StackDumper.dump("Found empty line");
}
sysOutClean.println(line);
}));
System.setOut(sysOutReplacement.toPrintStream());
Now if there's something like this:
System.out.println("ABC");
System.out.println("123");
System.out.println("");
System.out.println("DEF");
Then your console will look like this:
ABC
123
+----------\
| Found empty line
| at package.MyClass.myMethod(MyClass.java:62)
| (the rest of the stacktrace)
+----------/
DEF
You could implement your own PrintStream and use System.setOut to replace the default stdout. Then either put a debugging marker inside the class (if an empty string is printed), or print out the method name through the call stack (throw and catch an exception and get the stack information).
Example:
/** Control sysout prints */
public static void main(String[] arg) throws Exception {
System.out.println("Default"); //print normally
SysOutController.setSysOutLocationAddressor();
System.out.println("With Address"); //prints with calling location, and on click location cursor directly focus when System.out.**() called
SysOutController.ignoreSysout();
System.out.println("Ignored"); //this line will never prints
SysOutController.resetSysOut();
System.out.println("Default"); //print normally as it is (reset)
}
Just call methods of following class, which helps developers to controll sysout
import java.io.FileDescriptor;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintStream;
/**
* Class which controls System.out prints in console <br/>
* this class will helps developers to control prints in console
* #implSpec
* <pre><code>
* System.out.println("Default"); //print normally
*
* SysOutController.setSysOutLocationAddressor();
* System.out.println("With Address"); //prints with calling location
*
* SysOutController.ignoreSysout();
* System.out.println("Ignored"); //this line will never prints
*
* SysOutController.resetSysOut();
* System.out.println("Default"); //print normally as it is (reset)
* </code></pre>
* #author Dharmendrasinh Chudasama
*/
public class SysOutController {
private static void setOut(OutputStream out){
System.setOut(new PrintStream(out));
}
private static final OutputStream CONSOLE = new FileOutputStream(FileDescriptor.out);
/**
* Reset System.out.print* method
* #author Dharmendrasinh Chudasama
*/
public static void resetSysOut() { setOut(CONSOLE); }
/**
* System.out.print* will not print anything in console
* #author Dharmendrasinh Chudasama
*/
public static void ignoreSysout() {
setOut(new OutputStream() {
#Override public void write(int b) throws IOException {}
});
}
/**
* Address/location of calling System.out.* method will append in console
* #author Dharmendrasinh Chudasama
*/
public static void setSysOutLocationAddressor() {
setOut(new OutputStream() {
#Override
public void write(int b) throws IOException {
if(b=='\n'){ //if newLine
final StackTraceElement callerStEl = new Throwable().getStackTrace()[9];
String pathData =
"\u001B[37m" //low-visibality
+ "\t :: ("+callerStEl.getFileName()+":"+callerStEl.getLineNumber()+") ["+callerStEl+"]" //code path
+ "\u001B[0m "; //reset
CONSOLE.write(pathData.getBytes());
}
CONSOLE.write(b);
}
});
}
}
This can be due to some of the library also,if you feel that it is because of only System.out.println then,
Solution 1 :
Below code snippet should help you to find out the place where it is getting executed.
import java.io.FileNotFoundException;
import java.io.PrintStream;
public class CustomPrintStream extends PrintStream {
public CustomPrintStream(String fileName) throws FileNotFoundException {
super(fileName);
}
#Override
public void print(String s) {
try{
if(s == null || s.equals("")){
throw new Exception("Invalid print message");
}
super.print(s);
}catch(Exception e){
//TODO Change to your logger framework and leave it as same
e.printStackTrace();
}
}
public static void main(String[] args) {
try {
//TODO : Change to your favorite path and make sure mentioned
//file is available
CustomPrintStream customPrintStream = new CustomPrintStream
("/home/prem/Desktop/test.log");
System.setOut(customPrintStream);
System.out.println("");
} catch (FileNotFoundException e) {
//TODO Change to your logger framework and leave it as same
e.printStackTrace();
}
}
}
Solution 2 :
Since IDE's are available,please get the help from them.If you are using eclipse
Menu -> Search - > File Search-> Place System.out.println(""); in containing search and search for it.
I would rather say not to use the System.out.println in any of the code,for which you can make use of checkstyle and be confident that hence forth no developers use them.
Define a class NewPrintStream extends PrintStream
import java.io.FileNotFoundException;
import java.io.PrintStream;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class NewPrintStream extends PrintStream {
private static final Logger LOGGER = LoggerFactory.getLogger(NewPrintStream.class);
public NewPrintStream(String fileName) throws FileNotFoundException {
super(fileName);
}
#Override
public void println(String x) {
LOGGER.info("xxxxxxx", new Exception("xxxx"));
}
}
Then in main class set stdout/stderr print stream
System.setOut(new NewPrintStream("aaa"));
System.setErr(new NewPrintStream("aaa"));
Put a conditional breakpoint in PrintStream.println(String x) with the condition set to x.equals("") or whatever your string may be.
When I run the code below I get the following error.
C:\Documents and Settings\BOS\Desktop\test>java -jar test.jar
Exception in thread "main" java.lang.NullPointerException
at sun.launcher.LauncherHelper.getMainClassFromJar(Unknown Source)
at sun.launcher.LauncherHelper.checkAndLoadMain(Unknown Source)
I've got these files in \test directory = crimson.jar robosuite-api.jar and test.jar.
Here is the example they give to launch a robot?
import com.kapowtech.robosuite.api.java.rql.*;
public class SimpleRunRobot {
public static void main(String[] args) {
if (args.length < 1) {
System.out.println("Usage: RunRobot <robotURL>");
System.exit(1);
}
try {
// Run the robot
RQLResult result =
RobotExecutor.getRobotExecutor().execute(args[0]);
// Output the results
System.out.println(result);
}
catch (RQLException e) {
System.out.println("An error occurred: " + e);
}
}
}
Why is this giving me that Unknown Source error?
package robosuite.robots;
import com.kapowtech.robosuite.api.java.rql.RQLException;
import com.kapowtech.robosuite.api.java.rql.RQLResult;
import com.kapowtech.robosuite.api.java.rql.RobotExecutor;
import com.kapowtech.robosuite.api.java.rql.construct.RQLObjects;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
/**
*
* <p>
* This is an autogenerated class. It has been generated from the
* <code>library:/test.robot</code> file.
*
* #author RoboSuite
*/
public class Test {
// ----------------------------------------------------------------------
// Class fields
// ----------------------------------------------------------------------
private static final String ROBOT_URL = "library:/test.robot";
private static final RobotExecutor ROBOT_EXECUTOR = RobotExecutor.getRobotExecutor(SingletonRQLEngine.getInstance());
private static final Converter CONVERTER = Converter.getInstance();
// ----------------------------------------------------------------------
// Constructors
// ----------------------------------------------------------------------
/**
* Creates a new Test instance that can be used to execute the
* <code>library:/test.robot</code>.
*/
public Test() {
}
// ----------------------------------------------------------------------
// Instance methods
// ----------------------------------------------------------------------
/**
* Executes this robot.
*
* #param test an input object to the robot.
* #return an array of output objects.
* #throws java.io.IOException if the execution fails for some reason.
*/
public Testst[] run(Test0 test) throws java.io.IOException {
try {
// Prepare input objects
List parameters = new ArrayList();
parameters.add(test);
RQLObjects inputObjects = CONVERTER.convertBeansToRQLObjects(parameters);
// Run robot
RQLResult rqlResult = ROBOT_EXECUTOR.execute(ROBOT_URL, inputObjects);
// Extract output objects
RQLObjects outputObjects = rqlResult.getOutputObjects();
List result = CONVERTER.convertRQLObjectsToBeans(outputObjects);
return (Testst[]) result.toArray(new Testst[result.size()]);
} catch (RQLException e) {
throw new IOException(e.toString());
}
}
/* ------------------------------------------------------------------- */
}
If your using Java 7, Read this.
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7067922
Try
java -cp test.jar
include your other .jar files also
If you are using a manifest file make sure you have defined your main class.
for e.g.
Main-Class: test.MyApp
You have to add the name of the class having main() method in META-INF/manifest file.
Here is the link with more information :
http://java.sun.com/developer/Books/javaprogramming/JAR/basics/manifest.html
Thanks.
Why is this giving me that Unknown Source error?
The "unknown source" messages are not an error. It is the JVM telling you that the code that you are executing was compiled without any debug information; e.g. with the -gLnone option. As a result, the source file names and line numbers that would normally be included in the stacktrace are not available.
In this case, the code is some platform specific stuff that is internal to the JVM. Don't worry about it ...