Java：如何在单个文本文件中打印升序列，然后在该列的旁边打印同一组整数，除了按降序排列

Question

I need some help in how to do a certain step as I can not seem to figure it out. I was given a text file with 100 numbers in it all random, I am supposed to sort them either in ascending order, descending order, or both depending on the user input. Then which ever the user inputs the set of integers will be sorted and printed in a text file. I am having trouble printing the both file. Here is my code up until the both statement.

public static void print(ArrayList<Integer> output, String destination){
    try {
        PrintWriter print = new PrintWriter(destination);
        for(int i = 0; i < output.size(); i++){
            print.print(output.get(i) + " ");
        }
        print.close();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}


public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    BufferedReader br = null;
    ArrayList<Integer> words = new ArrayList<>();
    BufferedReader reader;
    String numbers;

    try {
        reader = new BufferedReader(new FileReader("input.txt"));

        while((numbers = reader.readLine()) != null)
        {
            words.add(Integer.parseInt(numbers));
        }

        System.out.println("How would you like to sort?");
        System.out.println("Please enter asc(For Ascending), desc(For Decending), or both");
        String answer = input.next();

        Collections.sort(words);

        if(answer.equals("asc")){
            Collections.sort(words);
            System.out.println(words);
            print(words,"asc.txt");
        }
        else if(answer.equals("desc")){
            Collections.reverse(words);
            System.out.println(words);
            print(words,"desc.txt");

When I type in "both" the text file that is created only has one column set of integers that is going in descending order, not both and I have no idea how to print both sets. If someone could shed some light I would really appreciate it.

else if(answer.equals("both")){
            System.out.println(words);
            print(words,"both.txt");
            Collections.reverse(words);
            System.out.println(words);
            print(words,"both.txt");

Answer 1

You need to use FileOutputStreams#Constructor where you can pass a boolean value to tell whether to append to my file or not.

So use like this:

PrintWriter print = new PrintWriter(new FileOutputStream(destination, true)); 
                                                                      /\
                                                                      ||
                                                                      ||
                                                             To append to the file

From JavaDocs

public FileOutputStream(File file,
                boolean append)
                 throws FileNotFoundException

Parameters:

file - the file to be opened for writing.

append - if true, then bytes will be written to the end of the file rather than the beginning