打印到系统和PrintWriter

Question

I have just over 100 lines of data and statistics that I need to print. I'm using:

PrintWriter p = new PrintWriter(fileName);

The reason why it's about 100 lines is because I need to print to both the System and the file (about 50 lines each). Is there any shorter way to print and "prettify" up my code?

System.out.println("Prints Stats"); //To System
p.println("Prints Stats"); //To File
etc

For every line printed to the System, there is an exact same line that is printed to the file. Is there a way to combine the two or to make it shorter? Or am I just stuck with this "ugly", long pile of prints?

Answer 1

There are several ways to do this.

Using a StringBuilder

If you are not writing tons of text, you could use a StringBuilder to create your output by appending to it, inserting stuff inside it etc., and once it's ready, print it to both p and System.out .

StringBuilder b = new StringBuilder();
b.append("Name: ").append("Susan").append("\n");
// Append more stuff to b, also insert and delete from it if you want.
System.out.print(b);
p.print(b);

Writing your own println()

If you're using just the println() method, you could write your own method that calls it for both writers:

private void println( String s ) {
    System.out.println(s);
    p.out.println(s);
}

That is, assuming p is a field and not a local variable.

Using format

Instead of using println() you could use the printf() or format() methods. The first parameter is a formatting string, and you can format several lines within one print using a format string. For example:

System.out.printf( "Name: %s%nSurname: %s%nAge: %d%n", "Susan", "Carter", 30 );

Would print

Name: Susan
Surname: Carter
Age: 30

And by using the same format string you can use two printf s to save on many println s:

String formatString = "Name: %s%nSurname: %s%nAge: %d%n";
Object[] arguments = { "Susan", "Carter", 30 );

p.printf( formatString, arguments );
System.out.printf( formatString, arguments );

This would print the above three-line output to your file and then to your System output.