System.out.printf(“%4d”) in BufferedWriter / FileWriter

Question

I made a multiplication table. The problem is that the table is not ordered as it should.

If I want just to print it on the screen, then I use this System.out.printf(“%4d”). How can I resolve this problem with BufferedWriter?

Instead of this:

Irj be egy szamot:
5
1 2 3 4 5 
2 4 6 8 10 
3 6 9 12 15 
4 8 12 16 20 
5 10 15 20 25 `

I want this:

Irj be egy szamot: 
5
1  2  3  4  5 
2  4  6  8 10 
3  6  9 12 15 
4  8 12 16 20 
5 10 15 20 25 `

Here is my code:

public class EgyszerEgy {
    public static void main(String[] args) {

        int a;
        int b;

        try {
            FileWriter writer = new FileWriter("EgyszerEgy.txt");
            BufferedWriter bf = new BufferedWriter(writer);

            Scanner tastatur = new Scanner(System.in);
            System.out.println("Irj be egy szamot: ");
            int szam = tastatur.nextInt();

            for (a = 1; a <= szam; ++a) {
                for (b = 1; b <= szam; ++b) {
                    int eredmeny = a * b;
                    String eredmenyString = String.valueOf(eredmeny);
                    bf.write(eredmenyString);
                    bf.write(" ");
                }
                bf.newLine();
            }
            bf.flush();
            bf.close();
        } catch (Exception e) {

        }

        // Kiolvasas
        //String result;
        try {
            FileReader fr = new FileReader("EgyszerEgy.txt");
            BufferedReader br = new BufferedReader(fr);
            String result;
            while ((result = br.readLine()) != null) {
                System.out.println(result);
            }
            br.close();
        } catch (Exception e) {

        }
    }
}

Replace `System.out.println(result);` with `System.out.printf("%4d", result);`. — Arvind Kumar Avinash, Apr 15 '20 at 11:06
Also: https://stackoverflow.com/questions/38416078/buffered-writer-vs-sys-out-print — Marvin, Apr 15 '20 at 11:07
@MaartenBodewes So Marvin did better than Marvin *(same person)*? — Andreas, Apr 15 '20 at 11:17
I think I'm faster in spotting my errors than you are, too late **again** :P — Maarten Bodewes, Apr 15 '20 at 11:25
Note that although both Marvin's suggestions have good answers, the questions themselves are very unwieldy and badly formatted. **Both are about streams as well instead of writers.** — Maarten Bodewes, Apr 15 '20 at 11:28

score 4 · Accepted Answer · answered Apr 15 '20 at 11:12

You already know how to wrap a FileWriter with a BufferedWriter. Now wrap it again with a PrintWriter, which has the printf() methods.

You should also use try-with-resources. It was added in Java 7, so there is absolutely no good reason not to use it, unless you're stuck on Java 6 or earlier.

Same for using NIO.2 API instead of the old File I/O API.

Scanner tastatur = new Scanner(System.in);
System.out.println("Irj be egy szamot: ");
int szam = tastatur.nextInt();

try (PrintWriter fout = new PrintWriter(Files.newBufferedWriter(Paths.get("EgyszerEgy.txt")))) {
    for (int a = 1; a <= szam; ++a) {
        for (int b = 1; b <= szam; ++b) {
            int eredmeny = a * b;
            fout.printf("%3d ", eredmenyString);
        }
        fout.println();
    }
}

Maarten Bodewes · Answer 2 · 2020-04-15T11:13:24.467

1

You can create the exact same formatting as printf by using String.format and writing the result to the BufferedWriter.

edited Apr 15 '20 at 11:13

answered Apr 15 '20 at 11:06

Maarten Bodewes

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Why would you need to use `String.format` explicitly? Why not just use a `PrintStream`? – Andy Turner Apr 15 '20 at 11:11
To get the spacing that the question asks for without doing anything differently. It wants `"%4d"` after all. – Maarten Bodewes Apr 15 '20 at 11:12
Either use `String.format` *or* use `PrintWriter.printf`. Doing both is redundant! – Andreas Apr 15 '20 at 11:13

System.out.printf(“%4d”) in BufferedWriter / FileWriter

2 Answers2