尽管没有抛出异常，但PrintWriter的输出文件不存在

Question

I have just started learning Java and I have got following problem I have been struggling for hours with. I want to use PrintWriter in order to produce a simple text file.

I do not get any runtime exception, still the file is not appearing in the specified directory.

public class Main {
    public static void main(String[] args) {
        try (final PrintWriter writer = new PrintWriter(
                new File("c:\test\new\notes.txt"))) {
            writer.write("Test note");
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

What am I doing wrong?

Answer 1

\\ represents an escape character so needs to be escaped itself for literal backslash characters. You can also use / and Java will resolve the correct separation character for the platform

try (final PrintWriter writer = new PrintWriter("c:\\test\new\\notes.txt")) {

Answer 2

在writer.write("Test note") writer.flush()之后添加writer.flush() ， writer.write("Test note") Windows路径使用双反斜杠（如其他答案所示）。

Answer 3

As Reimeus already said, \\ is an escape character in java. That means that a string containing "\\n" or "\\t" does not represent the stringliteral \\n or \\t!

'\\n' represents the newline character and '\\t' represents the TAB character!

For the better understanding, the following code:

System.out.println("c:\test\new\notes.txt");

would not print c:\\test\\new\\notes.txt to the console, it would print

c:    est
ew
otes.txt

to the console!

To be able to write the backslash in a string you'll need to use '\\\\' !

Answer 4

I see your question as having 2 parts:

1. Why doesn't the code work?
2. Why was no exception thrown?

The first question has already been answered, but I think the answer to the second question is at least as important because your current code will still fail silently if there is any problem writing to the file.

From the documentation of PrintWriter ( http://docs.oracle.com/javase/7/docs/api/java/io/PrintWriter.html ):

Methods in this class never throw I/O exceptions, although some of its constructors may. The client may inquire as to whether any errors have occurred by invoking checkError().

Therefore it is essential that you call checkerror() after every call to a PrintWriter method or your code will not be reliable.