在输入文本文件上写行号

Question

I need to write a program that will produce a new file where each line of text has a line number, given an input file with no line numbers. For example:

Given line: "sixteen"

Output line: " 1 | sixteen",

Line numbers are formatted right-aligned in 3 spaces, followed by a | character (with one space before
and after), and followed by the text in that line.

public class LineNumbers {
public static void process(File input, File output) {
    Scanner scanner;
    PrintWriter writer;
    try {
        scanner = new Scanner(input);
    } catch (FileNotFoundException e) {
        return;
    }
    try {
        writer = new PrintWriter(output);
    } catch (FileNotFoundException e) {
        return;
    }

    for (int i = 1; scanner.hasNextLine(); i++) {
        String s1 = scanner.nextLine();
        String s2 = "   " + i + " | " + s1;
        writer.print(s2);
    }
    scanner.close();
    writer.close();
}
}

This is the code I have, where the string s2 == the output I need, but how do I transition this into an output file?

*****EDIT*****

This is one of the tests that needs to be run, where only one line is input in the file. However, in the tester, it only has two spaces in front of the line number, and when I change my code to match, the test passes. All the other testers are written similarly and I think that may be causing the issue

    @Test
public void testOneLine() {
    try {
        // create file
        File        input  = folder.newFile( "input.txt" );
        File        output = folder.newFile( "output.txt" );

        PrintWriter write  = new PrintWriter( input );
        write.println( "Lorem ipsum dolor sit amet, consectetur adipiscing elit." );
        write.close();

        // invoke program
        LineNumbers.process( input, output );

        // verify file results
        assertTrue  ( "Output file does not exist", output.exists() );
        Scanner scan     = new Scanner( output );
        String[] result = new String[] { 
                "  1 | Lorem ipsum dolor sit amet, consectetur adipiscing elit."
        };
        for (String expected : result) {
            if (scan.hasNext()) {
                String actual = scan.nextLine();
                assertEquals( "Incorrect result", expected, actual );
            }
            else {
                fail( String.format( "Unexpected end of file: expected \"%s\"", expected ));
                break;
            }
        }
        assertFalse ( "File contains more data than expected", scan.hasNext() );
        scan.close();
    } 
    catch (IOException e) {
        fail( "No exception should be thrown" );
    }
}

Answer 1

You have too many spaces preceding your line number. When you are told to provide the line number in three spaces, it should be formatted as in one of these examples:

__1

_22

333

So that there are three characters total, including any spaces.