Using FileReader causes a compiler error “unhandle

问题:

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.

回答1:

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 {

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".

回答2:

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); 
}

回答3:

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);
    }
}

回答4:

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).

回答5:

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.

回答6:

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);
    }