Develop Reference

Unhandled exception type FileNotFoundException when trying to get a text file [duplicate]

Ive read a few threads here that relate the same problem, but the solutions arent working. :/
I use Eclipse, here is my program.
package mypackage;
import java.io.*;
public class myclass {
public static void main(String[] args) {
//String myfile = "/home/jason/workspace/myproject/src/mypackage/myscript.abc";
String myfile = "src/mypackage/myscript.abc";
File file1 = new File(myfile);
if(file1.exists()) {
log(myfile + " exists. length : " + myfile.length());
}
else{
log(myfile + " does not exist");
//System.exit(1);
}
//FileReader fr = new FileReader("myscript.abc");//I uncomment this and die inside
System.out.println("\nAbsPath : " + new File(".").getAbsolutePath());
System.out.println("\nuser.dir : " + System.getProperty("user.dir"));
}
public static void log(String s){
System.out.println(s);
}
}
The error I get, no matter what I try, or where I put myscript.abc (its peppered throughout the projects directory now) is this :
Unhandled exception type
FileNotFoundException myclass.java /myproject/src/mypackage
Wits end, pulling hairs.

Unhandled exception type FileNotFoundException myclass.java /myproject/src/mypackage
This is a compiler error. Eclipse is telling you that your program does not compile to java byte code (so of course you can't run it). For now, you can fix it by simply declaring that your program may throw this exception. Like so:
public static void main(String[] args) throws FileNotFoundException {
FileNotFoundException is a "checked exception" (google this) which means that the code has to state what the JVM should do if it is encountered. In code, a try-catch block or a throws declaration indicate to the JVM how to handle the exception.
For future reference, please note that the red squiggly underline in Eclipse means there is a compiler error. If you hover the mouse over the problem, Eclipse will usually suggest some very good solutions. In this case, one suggestion would be to "add a throws clause to main".

Use the file descriptor that you created and verified before creating the file reader. Also, you will probably run into problems using relative paths. Why is the line with the full path commented out? In any case, here is the code:
if(file1.exists()) {
log(myfile + " exists. length : " + myfile.length());
FileReader fr = new FileReader(file1);
}

I see that you tried to specify the full path to your file, but failed because of the following mistake:
you haven't declared or tried to catch java.io.FileNotFoundException.
To fix it, you can replace the line
FileReader fr = new FileReader("myscript.abc");
with the code:
try {
FileReader fr =
new FileReader("/home/jason/workspace/myproject/src/mypackage/myscript.abc");
} catch (FileNotFoundException ex) {
Logger.getLogger(myclass.class.getName()).log(Level.SEVERE, null, ex);
}
The following code is successfully compiled, and it should work:
package mypackage;
import java.io.*;
// It's better to use Camel style name for class name, for example: MyClass.
// In such a way it'll be easier to distinguish class name from variable name.
// This is common practice in Java.
public class myclass {
public static void main(String[] args) {
String myfile =
"/home/jason/workspace/myproject/src/mypackage/myscript.abc";
File file1 = new File(myfile);
if (file1.exists()) {
log("File " + myfile + " exists. length : " + myfile.length());
} else {
log("File " + myfile + " does not exist!");
}
try {
FileReader fr = new FileReader(myfile);
} catch (FileNotFoundException ex) {
// Do something with mistake or ignore
ex.printStackTrace();
}
log("\nAbsPath : " + new File(".").getAbsolutePath());
log("\nuser.dir : " + System.getProperty("user.dir"));
}
public static void log(String s) {
System.out.println(s);
}
}

This is a compiler error. Eclipse is telling you that your program does not compile to java byte code (so of course you can't run it). For now, you can fix it by simply declaring that your program may throw this exception. Like so:
public static void main(String[] args) throws IOException{
}

You are expecting Eclipse to run the program in the project root directory. Unless you did something special with your "Run" configuration, I'd be suprised if it really starts there.
Try printing out your current working directory to make sure this is the right path.
Then try verifying that the bin / build directory contains your "*.abc" files, as they are not Java source files and may have not been copied into the compilation output directory.
Assuming that they are in the compliation directory, rewrite your file loader to use a relative path based on the class laoder's path. This will work well in exanded collections of .class files in directories (and later in packed JAR files).

Instead of trying to figure out what's going on, why not print what's going on...
Make this change to your code:
log(myfile.getName() + "(full path=" + myfile.getAbsolutePath() + ") does not exist");
You might find it either isn't using the directory you think, or (depending on your filesystem) it might be trying to create a file whose name is literally "src/mypackage/myscript.abc" - ie a filename with embedded slashes.

you can fix it simply declaring that throw this exception. Like this:
public static void main(String args[]) throws FileNotFoundException{
FileReader reader=new FileReader("db.properties");
Properties p=new Properties();
p.load(reader);
}

Java reflection - Android classes not found

I am trying to run reflection to check if some android class exists in Java ( such as Toast ). I am running it from my Command line using this code:
String [] packages = new String[] {"java.lang.",
"android.widget.",
"android.util.",
"android.app.",
"android.view.",
"android.content."};
for (int i = 0; i < packages.length; i++){
String package_name = packages[i];
try {
Class<?> clazz = Class.forName(package_name + "Toast");
System.out.println("class Exists");
return clazz;
}
catch (ClassNotFoundException e){
System.out.println("class " + package_name + "Toast doesnt exists");
}
}
However, I get the output:
class android.widget.Toast doesn't exists ( but I know it does this is where the class is at)
any ideas?
EDIT : I am trying to write a Java class that is not running from Android Studios, but compiles and runs using javac from cmd line.

Because you are executing this on the command line there is no reason the Android packages/classes should be available to the runtime unless it is explicitly included. The output of your program makes sense - unless you provide the correct Android libraries to the program then there is not going to be a match when you try to resolve a particular Android class such as Toast.
The answer is essentially using Java's classpath effectively. By default, without stating an argument, it is the working directory '.'.
Add to it using -classpath as an argument. Compile naively:
javac YourReflectionTest.java
as you know the program finds no matches.
If you do this javac will also succeed
javac -classpath ".;/opt/android-sdk/platforms/android-21/android.jar" YourReflectionTest.java
If you run the program, and try
java YourReflectionTest
It will still produce the same result. Why? At run-time, there are still no Android classes loaded. You are by default only going to get the java system libraries included in your installation of JDK.
But, if you provide an appropriate path at runtime, then suddenly all the magic happens:
java -classpath ".;/opt/android-sdk/platforms/android-21/android.jar" YourReflectionTest
Note, Android API level 21 is just an example here and any could be used depending on which features you're trying to test.

When I execute your code, I get get this output:
class java.lang.Toast doesnt exists
class Exists
Since you iterate over all packages, you get an output for every package, no matter if your class exists or not, and you only stop when you find a match.
I think what you are trying to achieve is to always get only 1 output: either the class exists, or it doesn't. You could do that by creating a method classExists() and then using the java stream API to find if any of your packages contains your class Toast:
public void myMethod() {
List<String> packages = Arrays.asList(
"java.lang.",
"android.widget.",
"android.util.",
"android.app.",
"android.view.",
"android.content."
);
String className = "Toast";
if (packages.stream().anyMatch(pkg -> classExists(pkg + className))) {
System.out.println("class exists");
} else {
System.out.println("class doesnt exist");
}
}
boolean classExists(String fullClassName) {
try {
Class.forName(fullClassName);
return true;
} catch (ClassNotFoundException e) {
return false;
}
}

A simple method using reflection to check if a class exists or not:
private boolean doesClassExist(String name) {
try {
Class c = Class.forName(name);
if (c != null) {
return true;
}
} catch (ClassNotFoundException e) {
// Class not found
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
return false;
}
Use Case:
boolean classExists = doesClassExist("android.widget.Toast");

Execute Jar file in IDE and get the output (String)? [duplicate]

This question already has answers here:
Execute .jar file from a Java program
(10 answers)
Closed 6 years ago.
Is it possible to execute a Jar file on my IDE (IntelliJ) to get the output string for my own purpose on the project that I have?
I know that we can make system calls, but in this case I want to add a Jar file on my project and execute it whenever I want it.
For example: I have a project on IntelliJ, one of my classes (on this project) needs to get the output by running the Jar file (which is on my project).
On my terminal, I would do something like java -jar <jar_file>.jar <file>.asm and this would output a result to my terminal.
And I want to get that output from this command on my Java Class.

Your Jar file returns an output string, so I assume, it's main-method could look like:
public static void main(String[] args) {
System.out.println("output string");
}
And now, if you want to use this "output string" string in your own class, you could do it like this:
public class YourClass {
...
public String getOutputStringFromJar() {
String s = ""; // or = null;
try {
Process p = Runtime.getRuntime().exec("java -jar full/path/to/your/Jar.jar full/path/to/fibonacci.asm");// just like you would do it on your terminal
p.waitFor();
InputStream is = p.getInputStream();
byte b[] = new byte[is.available()];
is.read(b, 0, b.length); // probably try b.length-1 or -2 to remove "new-line(s)"
s = new String(b);
} catch (Exception ex) {
ex.printStackTrace();
}
return s;
}
...
}
Now you have the method, that returns the output string, and you can use it however you want, and you know how to execute a Jar file from your project whenever you want

Your ask is not precise, but if i understand what you're doing, you run the Mars.jar with .asm file in param, and you got an output like in the this link with Fibonacci numbers
and now you want to get the Fibonacci numbers in your program? if that is what you need, i would suggest you to decompile the jar to understand his content
When you do so, you'll see that the main class in the jar is like this
public class Mars {
public static void main(String[] args) {
new mars.MarsLaunch(args);
}
}
so simply when you add the jar to your class path, you need to do somthing like this
public static void main(String[] args) throws FileNotFoundException {
// this will redirect your system output to a file named output.txt
PrintStream out = new PrintStream(new FileOutputStream("output.txt"));
System.setOut(out);
String [] myAsmFile = {"C:/produits/Fibonacci.asm"};
new mars.MarsLaunch(myAsmFile);
// and then you can read the output.txt file
}
hope this help you

input from file in java

I am java beginner learner and i am trying to output the data on file which i call a.txt. need help i have no idea y i am getting exception error file not open . i put a.txt in the same directory in which i have main and readfile.
- main path : C:\Users\Navdeep\Desktop\java\assign1\src\assign1
- readfile : C:\Users\Navdeep\Desktop\java\assign1\src\assign1
- a.txt : C:\Users\Navdeep\Desktop\java\assign1\src\assign1
Thanks in advance .
main.java
package assign1;
public class main {
public static void main(String[] args) {
readfile r = new readfile();
r.openFile();
r.readFile();
r.closeFile();
}
}
readile.java
package assign1;
import java.io.*;
import java.util.*;
public class readfile {
private Scanner x;
public void openFile() {
try {
x = new Scanner(new File("a.txt"));
} catch (Exception e) {
System.out.println("file not open \n");
}
}
public void readFile() {
while (x.hasNext()) {
String Agent = x.next();
String request_type = x.next();
String classtype = x.next();
String numberofseat = x.next();
String arrivaltime = x.next();
System.out.printf("%s %s %s %s %s \n", Agent,
request_type, classtype, numberofseat, arrivaltime);
}
}
public void closeFile() {
x.close();
}
}
a.txt
1 r e 1 0
2 r e 1 1

If you use a File with a relative path, it is assumed relative to the "current user directory". What's the "current user directory"? See the doc:
A relative pathname, in contrast, must be interpreted in terms of information taken from some other pathname. By default the classes in the java.io package always resolve relative pathnames against the current user directory. This directory is named by the system property user.dir, and is typically the directory in which the Java virtual machine was invoked.
Also from the doc:
On UNIX systems, a relative pathname is made absolute by resolving it against the current user directory. On Microsoft Windows systems, a relative pathname is made absolute by resolving it against the current directory of the drive named by the pathname, if any; if not, it is resolved against the current user directory.
So one way to get the File to be found using a relative path would be to start the JVM in the directory with the file.
However, this approach can be kind of limiting since it constrains you to always start the JVM in a certain directory.
As an alternative, you might consider using ClassLoader#getResourceAsStream. This allows you to load any resource that is on the JVM's "classpath". The classpath can be configured in a number of different ways, including at launch time using arguments to the JVM. So I would suggest using that, rather than initializing your Scanner with a File. This would look like:
InputStream is = StackOverflow.class.getClassLoader().getResourceAsStream("a.txt");
Scanner scanner = new Scanner(is);
Now, when using getResourceAsStream, you have to make sure that the file referenced is on the classpath of the Java Virtual Machine process which holds your program.
You've said in comments that you're using Eclipse.
In Eclipse, you can set the classpath for an execution by doing the following:
1) After running the program at least once, click on the little dropdown arrow next to the bug or the play sign.
2) Click on "Debug configurations" or "Run Configurations".
3) In the left sidebar, select the run configuration named after the program you're running
4) Click on the "Classpath" tab
5) Click on "User Entries"
6) Click on "Advanced"
7) Select "Add Folders"
8) Select the folder where a.txt resides.
Once you have done this, you can run the program using the run configuration you have just set up, and a.txt will be found.
Basic idea of classpath
The classpath represents the resources that the JVM (Java Virtual Machine) holding your program knows about while it's running. If you are familiar with working from a command line, you can think of it as analogous to your OS's "PATH" environment variable.
You can read about it in depth here.

Instead of putting the file in src folder put the txt file in the project ie outside the src.

Here is one using BufferedReader.
public static void main(String[] args) {
// check for arguments. this expects only one argument #index [0]
if (args.length < 1) {
System.out.println("Please Specify your file");
System.exit(0);
}
// Found atleast one argument
FileReader reader = null;
BufferedReader bufferedReader = null;
// Prefer using a buffered reader depending on size of your file
try {
reader = new FileReader(new File(args[0]));
bufferedReader = new BufferedReader(reader);
StringBuilder content = new StringBuilder();
String line;
while ((line = bufferedReader.readLine()) != null)
content.append(line);
System.out.println(content.toString());
} catch (IOException e) {
e.printStackTrace();
} finally {
// dont forget to close your streams
try {
if (bufferedReader != null)
bufferedReader.close();
if (reader != null)
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
Let me know if you have any isues.
Good_luck_programming!

How to run compilr.com java .jar executable on windows when its not just java.lang* package

I'm starting to code in Java in spare work time. Problem is everything is locked down and I'm kinda new to ask IT department to install ide or javac at least to me(im not in IT) so Im using Compilr.com which is quite awesome. Yet I tried to save and run the Hello world code already precoded there:
public class ReadFile
{
public static void main(String args[])
{
System.out.println("Hello World from Compilr!");
System.out.println("Press any key to continue.");
try {
System.in.read();
} catch (Throwable t) {}
}
}
Then open windows cmd and run java -jar HelloWorld.jar Which Works.
Then I tried to build and run this code which throws the typical error that I havent properly setup classpath or some manifest made:
import java.io.*;
public class ReadFile{
public static void main(String[] args){
try {
FileReader input = new FileReader(args[0]);
BufferedReader bufRead = new BufferedReader(input);
String line;
int count = 0;
line = bufRead.readLine();
count++;
// Read through file one line at time. Print line # and line
while (line != null){
System.out.println(count+": "+line);
line = bufRead.readLine();
count++;
}
bufRead.close();
}catch (ArrayIndexOutOfBoundsException e){
System.out.println("Usage: java ReadFile filename\n");
}catch (IOException e){
// If another exception is generated, print a stack trace
e.printStackTrace();
}
}// end main
}
The thing it only generates a jar file so I dont have much of choice for compiling. How do I please make working code with all the available non-core java clasess?
/At home I get error even on the helloworld program: Error:Could not find or load main class Program.

You should be able to install both JDK with Netbeans and Eclipse in a local directory without admin rights. While it will be interesting to find out why compilr.com generated jar does not work for you for any serious work you will need a development environment.