Bad practice in JDK's try-with-resources example? [duplicate]

Question

I found this example in the try-with-resources documentation for Java:

static String readFirstLineFromFile(String path) throws IOException {
    try (BufferedReader br = new BufferedReader(new FileReader(path))) {
        return br.readLine();
    }
}

If the constructor for BufferedReader throws an exception, then the resources held by the FileReader won't be released. So isn't this a bad practice to write it like that instead of:

static String readFirstLineFromFile(String path) throws IOException {
    try (FileReader fr = new FileReader(path);
         BufferedReader br = new BufferedReader(fr)) {
        return br.readLine();
    }
}

Answer 1

Indeed, just gave it a quick try:

public class MyFileReader extends FileReader {

    public MyFileReader(String fileName) throws FileNotFoundException {
        super(fileName);
    }

    @Override
    public void close() throws IOException {
        System.out.println("Closing MyFileReader");
        super.close();
    }

}

public class MyBufferedReader extends BufferedReader {

    public MyBufferedReader(Reader in) {
        super(in);
        throw new RuntimeException();
    }

    @Override
    public void close() throws IOException {
        System.out.println("Closing MyBufferedReader");
        super.close();
    }

}

public String test(String path) throws IOException {
    try (BufferedReader br = new MyBufferedReader(new MyFileReader(path))) {
        return br.readLine();
    }
}

None of MyFileReader nor MyBufferedReader is closed... Good catch!

While with:

public String test(String path) throws IOException {
    try (FileReader fr = new MyFileReader(path); BufferedReader br = new MyBufferedReader(fr)) {
        return br.readLine();
    }
}

MyFileReader is closed.

BufferedReader constructor can indeed throw exceptions, see BufferedReader(Reader in, int sz) constructor (although not when coming from BufferedReader(Reader in) constructor, but the doc you linked should still alert on this possible issue IMHO).

Looks like you won the right to raise an issue :)