java - 文件输出时遇到问题

Question

我希望能够从文件中读取 20 个随机名称并将它们放入一个新文件中。我该怎么办？

public class Assignment2 {

    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();
        }

        // Choose a random one from the list
        Random r = new Random();

        for (int i = 0; i < 20; i++) 
        {
           int rowNum = r.nextInt(lines.size ());
           System.out.println(lines.get(rowNum));
        }

    }
}

Answer 1

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

    Random random = new Random();

    for (int i = 0; i < 20; i++) {
       int rowNum = random.nextInt(lines.size());
       writer.write(lines.get(rowNum));
       writer.newLine();
    }
}

如果您需要检查某个号码是否已被使用，请将其添加到集合中:

try (BufferedWriter writer = new BufferedWriter(new FileWriter("randomNames.txt"))) {
    Set<Integer> usedNumbers = new HashSet<Integer>(20);
    Random random = new Random();
    int addedCount = 0;

    while (addedCount < 20) {
        int rowNum = random.nextInt(lines.size());
        if (usedNumbers.add(rowNum)) {
            writer.write(lines.get(rowNum));
            writer.newLine();
            addedCount++;
        }
    }
}

检查是否有另一个名称具有相同的第一个字符:

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

然后你就可以:

    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();
        }
    }