Java error: Default constructor cannot handle exce

问题:

I'm trying to read input from a file to be taken into a Java applet to be displayed as a Pac-man level, but I need to use something similar to getLine()... So I searched for something similar, and this is the code I found:

File inFile = new File("textfile.txt");
FileInputStream fstream = new FileInputStream(inFile);//ERROR
// Get the object of DataInputStream
DataInputStream in = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(in));

The line I marked "ERROR" gives me an error that says "Default constructor cannot handle exception type FileNotFoundException thrown by implicit super constructor. Must define an explicit constructor."

I've searched for this error message, but everything I find seems to be unrelated to my situation.

回答1:

Either declare a explicit constructor at your subclass that throws FileNotFoundException:

public MySubClass() throws FileNotFoundException {
} 

Or surround the code in your base class with a try-catch block instead of throwing a FileNotFoundException exception:

public MyBaseClass()  {
    FileInputStream fstream = null;
    try {
        File inFile = new File("textfile.txt");
        fstream = new FileInputStream(inFile);
        // Get the object of DataInputStream
        DataInputStream in = new DataInputStream(fstream);
        BufferedReader br = new BufferedReader(new InputStreamReader(in));
        // Do something with the stream
    } catch (FileNotFoundException ex) {
        Logger.getLogger(this.getClass().getName()).log(Level.SEVERE, null, ex);
    } finally {
        try {
            // If you don't need the stream open after the constructor
            // else, remove that block but don't forget to close the 
            // stream after you are done with it
            fstream.close();
        } catch (IOException ex) {
            Logger.getLogger(this.getClass().getName()).log(Level.SEVERE, null, ex);
        }
    }  
} 

Unrelated, but since you are coding a Java applet, remember that you will need to sign it in order to perform IO operations.

回答2:

You need to surround your code with try and catch as follows:

try {
    File inFile = new File("textfile.txt");
    FileInputStream fstream = new FileInputStream(inFile);//ERROR
} catch (FileNotFoundException fe){
    fe.printStackTrace();
}
// Get the object of DataInputStream
DataInputStream in = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(in));

回答3:

This is guesswork as we don't have the complete code.

From the Javadoc:

public FileInputStream(File file) throws FileNotFoundException

It means that when you do a new FileInputStream() like you do, it can come back with a FileNotFoundException. This is a checked exception, that you need to either rethrow (i.e. add 'throws FileNotFoundException' in the method where you do the new) or catch (see other try/catch responses).