java - Do I have to close FileOutputStream which is wrapped by PrintStream?

Question

I'm using FileOutputStream with PrintStream like this:

class PrintStreamDemo {  
    public static void main(String args[]) { 
        FileOutputStream out; 
        PrintStream ps; // declare a print stream object
        try {
            // Create a new file output stream
            out = new FileOutputStream("myfile.txt");

            // Connect print stream to the output stream
            ps = new PrintStream(out);

            ps.println ("This data is written to a file:");
            System.err.println ("Write successfully");
            ps.close();
        }
        catch (Exception e) {
            System.err.println ("Error in writing to file");
        }
    }
}

I'm closing only the PrintStream. Do I need to also close the FileOutputStream (out.close();)?

Answer 1

No, you only need to close the outermost stream. It will delegate all the way to the wrapped streams.

However, your code contains one conceptual failure, the close should happen in finally, otherwise it's never closed when the code throws an exception between opening and closing.

E.g.

public static void main(String args[]) throws IOException { 
    PrintStream ps = null;

    try {
        ps = new PrintStream(new FileOutputStream("myfile.txt"));
        ps.println("This data is written to a file:");
        System.out.println("Write successfully");
    } catch (IOException e) {
        System.err.println("Error in writing to file");
        throw e;
    } finally {
        if (ps != null) ps.close();
    }
}

(note that I changed the code to throw the exception so that you understand the reason of the problem, the exception namely contains detailed information about the cause of the problem)

Or, when you're already on Java 7, then you can also make use of ARM (Automatic Resource Management; also known as try-with-resources) so that you don't need to close anything yourself:

public static void main(String args[]) throws IOException { 
    try (PrintStream ps = new PrintStream(new FileOutputStream("myfile.txt"))) {
        ps.println("This data is written to a file:");
        System.out.println("Write successfully");
    } catch (IOException e) {
        System.err.println("Error in writing to file");
        throw e;
    }
}