Exception handling for createReader("notexisting.txt");

Programming Questions

gonras

Exception handling for createReader("notexisting.txt");

in Programming Questions • 1 year ago

Hello,

I want to use try and catch for the situations where is no text file to be found.

Sadly I can not get it to work. It is is not catching at all. can someone tell me how this works?

thank you very much :)

BufferedReader reader;
String line;

void setup() {
// Open the file from the createWriter() example
try {
reader = createReader("not_there.txt");
}
catch (Exception e) {
e.printStackTrace();
println("No file found"); // this should be displayed
}
}

void draw() {
if (dok) {
try {
line = reader.readLine();
}
catch (Exception e) {
println("bla"); // works well...
e.printStackTrace();
line = null;
}
if (line == null) {
// Stop reading because of an error or file is empty
noLoop();
}
else {
String[] pieces = split(line, TAB);
int x = int(pieces[0]);
int y = int(pieces[1]);
point(x, y);
}
}
}

Replies(3)

calsign

Re: Exception handling for createReader("notexisting.txt");

1 year ago

The function will return null, but will not cause an error...
The try / catch() statement should go around where the error actually occurs, or you should try to do something with the object. For example:

try {
reader = createReader("not_there.txt");
if(reader.equals("null")) println("No file found"); //Ironically, this causes the error we're looking for
} catch (NullPointerException e) {
e.printStackTrace();
println("No file found");
}

Also, if you know what kind of exception you're going to get, it makes for cleaner code, and more precision, to narrow it down to just filter for that exception. In this case, for example, it's a NullPointerException...

gonras

Re: Exception handling for createReader("notexisting.txt");

1 year ago

I is a little weird, but it works.

Thank you very much !

PhiLho

Re: Exception handling for createReader("notexisting.txt");

1 year ago

Don't use try / catch for a NullPointerException! It is much easier and faster to just check the variable for being null...
Try / catch should be used only for exceptions that are mandatory to catch or those you have no control over (I/O exceptions).

And indeed, Processing functions doesn't throw exceptions, they are caught and Processing tries to do a sane default behavior. If you want exceptions, use the Java I/O API directly.
Note: you can also check the existence of a file:
File f = dataFile("someFile.txt");
if (f.exists()) { ... }