Difference between java.io.PrintWriter and java.io

问题:

Please look through code below:

// A.class
File file = new File("blah.txt");
FileWriter fileWriter = new FileWriter(file);
PrintWriter printWriter = new PrintWriter(fileWriter);

// B.class
File file = new File("blah.txt");
FileWriter fileWriter = new FileWriter(file);
BufferedWriter bWriter = new BufferedWriter(fileWriter);

What is the difference between these two methods?

When should we use PrintWriter over BufferedWriter?

回答1:

The API reference for BufferedWriter and PrintWriter detail the differences.

The main reason to use the PrintWriter is to get access to the printXXX methods like println(). You can essentially use a PrintWriter to write to a file just like you would use System.out to write to the console.

A BufferedWriter is an efficient way to write to a file (or anything else), as it will buffer the characters in Java memory before (probably, depending on the implementation) dropping to C to do the writing to the file.

There is no such concept as a "PrintReader"; the closest you will get is probably java.util.Scanner.

回答2:

PrintWriter gives more methods (println), but the most important (and worrying) difference to be aware of is that it swallows exceptions.

You can call checkError later on to see whether any errors have occurred, but typically you'd use PrintWriter for things like writing to the console - or in "quick 'n dirty" apps where you don't want to be bothered by exceptions (and where long-term reliability isn't an issue).

I'm not sure why the "extra formatting abilities" and "don't swallow exceptions" aspects are bundled into the same class - formatting is obviously useful in many places where you don't want exceptions to be swallowed. It would be nice to see BufferedWriter get the same abilities at some point...

回答3:

As said in TofuBeer's answer both have their specialties. To take the full advantage of PrintWriter (or any other writer) but also use buffered writing you can wrap the BufferedWriter with the needed one like this:

PrintWriter writer = new PrintWriter(
                         new BufferedWriter (
                             new FileWriter("somFile.txt")));

回答4:

PrintWriter just exposes the print methods on any Writer in character mode.

BufferedWriter is more efficient than , according to its buffered methods. And it comes with a newLine() method, depending of your system platform, to manipulate text files correctly.

The BufferedReader permits to read a text from file, with bytes converted in characters. It allows to read line by line.

There is no PrintReader, you have to choose another Reader implementation according to the format of your input.

回答5:

In general, a Writer sends its output immediately to the underlying character or byte stream. Unless prompt output is required, it is advisable to wrap a BufferedWriter around any Writer whose write() operations may be costly, such as FileWriters and OutputStreamWriters. For example,

Note: Text content in the code blocks is automatically word-wrapped

PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("foo.out")));

will buffer the PrintWriter's output to the file. Without buffering, each invocation of a print() method would cause characters to be converted into bytes that would then be written immediately to the file, which can be very inefficient.

回答6:

BufferedWriter - Writes text to an output character stream, buffering characters from a character stream. PrintWriter - Prints formatted representations of objects to a text output stream.

回答7:

PrintWriter is the most enhanced Writer to write Character data to a file.

The main advantage of PrintWriter over FileWriter and BufferedWriter is:

1. PrintWriter can communicate directly with the file, and can communicate via some Writer object also.

PrintWriter printwriter = new PrintWriter("blah.txt");

(or)

FileWriter filewriter = new FileWriter("blah.txt");
PrintWriter printwiter = new PrintWriter(filewriter);

2. We can write any type of Primitive data directly to the file (because we have additional overloaded versions of PrintWriter methods i.e., print() and println()).

   printwriter.print(65); //65
bufferedwriter.write(65); //A
printwriter.println(true); //true

回答8:

I think that the reason behind using PrintWriter is already mentioned above but one of the important reason is you an pass a file object directly to the PrintWriter constructor which makes it easy to use it.

File file=new File(“newfile.txt”);
PrintWriter pw=new PrintWriter(file);