Question

I cannot figure out why the following simple program doesn’t (create) and then write to a file? Can you spot where the problem is?

public class RandomSeq
{
    public static void main( String[] args)
    {
        // command-line argument
        int N = Integer.parseInt( args[0] );

        // generate and print N numbers between 0 and 1
        for ( int i = 0 ; i < N; i++ )
        {
            // System.out.println( Math.random() );
            StdOut.println( Math.random() );
        }
    }
}

When I type the following at the Interactions prompt:

java RandomSeq 5

0.9959531649155268
0.5010055704125982
0.4444779637605908
0.4205901267129799
0.09968268057133955

I obviously get the correct output, but when I use piping, it doesn’t do what (I think) it should do:

> java RandomSeq 5 > f1.txt

Answer 1

The “normal” Java way to write to a file is by using a Writer class. I denoted a small example below. Alternatively you can change the PrintStream that you write to which then sends the output to a file instead of the console (essentially the same as below)

PrintWriter out;
File myfile = new File(folder,"output.txt");
myfile.createNewFile();
fos = new FileOutputStream(myfile);
out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(fos, "UTF-8")));
out.println("some text to go in the output file");

Edit:
On my machine the code works fine using System.out.println(). I can only imagine that there might be a problem with the write permissions, else wise maybe StdOut object has some bugs…

~/scratch $ java RandomSeq 5 > out.txt
~/scratch $ cat out.txt 
0.5674462012296635
0.05189786036638799
0.1290205079541452
0.22015961731674394
0.6503198654182695
~/scratch $