如何从两个不同的文件中读取文件，并将每个文件中的10个随机名称放到同一输出文件中，总共20个

Question

I am trying to read names in from a second file but only pick 10 randomly from each file for a total of 20 in the same output file. But can't figure out how to read from a second file and put into the same output.

public class example2 {

    public static void main(String[] args) throws IOException
    {
// Read in the file into a list of strings
        BufferedReader reader = new BufferedReader(new FileReader("textfile.txt"));
//BufferedWriter bw = new BufferedWriter(new FileWriter("out.txt"));
        List<String> lines = new ArrayList<String>();

        String line = reader.readLine();

        while( line != null ) {
            lines.add(line);
            line = reader.readLine();
        }

        try (BufferedWriter writer = new BufferedWriter(new FileWriter("randomNames.txt"))) {


            Random random = new Random();
            Set<String> usedNames = new HashSet<String>(20);

            while (usedNames.size() < 20) {
                int rowNum = random.nextInt(lines.size());
                String name = lines.get(rowNum);
                if (!containsNameWithSameFirstCharacter(usedNames, name)) {
                    usedNames.add(name);
                    writer.write(name);
                    writer.newLine();
                }
            }
            writer.flush();
        }

    }
    private static boolean containsNameWithSameFirstCharacter(Collection<String> names, String name) {
        for (String anotherName: names) {
            if (anotherName.charAt(0) == name.charAt(0)) {
                return true;
            }
        }
        return false;
    }
}

Answer 1

It seems to me that you'd be better off reading all of both files into two lists and then taking items from each until you have your output list.

Something like:

List<String> list1 = Files.readAllLines(path1);
List<String> list2 = Files.readAllLines(path2);
List<String> output = new ArrayList<>();
Collections.shuffle(list1);
Collections.shuffle(list2);
while (output.size() < 20) {
    addFromList(list1, output);
    addFromList(list2, output);
}

private void addFromList(List<String> from, List<String> to) {
    String name = from.remove(0);
    while (containsNameWithSameFirstCharacter(to, next))
        name = from.remove(0);
    to.add(name);
}

This needs some error checking for empty lists but hopefully you get the idea.

Answer 2

public static void main(String[] args){
    try {
        BufferedWriter writer = new BufferedWriter(new FileWriter(new File("outputfile.txt")));
        List<String> a = readFile(new File("textfile1.txt"));
        List<String> b = readFile(new File("textfile2.txt"));
        List<String> all = a;
        all.addAll(b);
        Random random = new Random();
        for(int i= 0; i < 10;){
            int l = random.nextInt(all.size() - 1);
            i++;
            String n = all.get(l);
            writer.newLine();
            writer.write(n);
        }
        writer.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

private static List<String> readFile(File file) throws IOException {
    Path p = Paths.get(file.toURI());
    List<String> ls = Files.readAllLines(p);
    return ls;
}

This will read the two files, get its contents, add them to a list, pick 10 of them, and write them to a file. One name = one line.

Of course this is not all your code for your purpose. This is just a starter that does the trick for you.