如何从一个文本文件中读取整数，将它们从最小到最大排序，然后将它们写入另一个文本文件

Question

I am attempting to write 100 random integers to one text file, sort them from least to greatest, and then write those numbers, sorted, to a separate text file. I understand how to write the numbers to one file, and how to sort them. Both files must be created by the program if they do not already exist. For instance if the "Numbers.txt" that I write the original 100 random integers on does not exist, the program will create the file for me, as same goes for the text file I am attempting to write the sorted numbers on. I am struggling to understand how to write the sorted numbers from one file to another.

I have attempted to take the same numbers from the integer array that the numbers are originally stored in, and sort it with the Arrays.sort command, and then write that information to the separate file which I wish to be called "Sorted.txt". I run into a problem there where I get an incompatible type error, stating void cannot be converted to int, but do not know how to fix this error in logic.

import java.util.*;
import java.io.*;

public class Numbers {
   public static void main(String[] args) throws Exception {
      //check if source file exists
      File number = new File("Numbers.txt");
      File sorted = new File("Sorted.txt");
      if (!number.exists()) {
         try ( // create the file
         PrintWriter output = new PrintWriter(number);
         ) {
            for (int i = 0; i <= 100; i++) {
               output.print(((int)(Math.random() * 999) + 1) + " ");
            }
         }
      }
      try (
      Scanner input = new Scanner(number);
      ) {
         int[] numbers = new int[100];
         for (int i = 0; i < 100; i++)
            System.out.print(numbers[i] + " ");

            System.out.println();

            if (!sorted.exists()) {
               try (
               PrintWriter output = new PrintWriter(sorted)
               ) {
                  for (int i = 0; i < 100; i ++) {
                     output.print((int)Arrays.sort(numbers));
                  }
            }
         }
      }
   }
}

The expected result is that the first text file shows the numbers as they were when they were randomly created, while the second text file shows them after they are sorted. As of current, I can get the first file to show the numbers in a random order, but cannot even get the second text file to be created, let alone the numbers sorted and wrote on it.

Answer 1

Arrays.sort returns void ( see doc ).

What you could do is sort the array. Arrays.sort(numbers);

And after write the result to a file.

for (int i = 0; i < 100; i ++) {
    output.print(numbers[i] + " ");
}

Complete Example:

import java.io.File;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Scanner;


public class Numbers {
   public static void main(String[] args) throws Exception {
      //check if source file exists
      File number = new File("Numbers.txt");
      File sorted = new File("Sorted.txt");
      if (!number.exists()) {
         try ( // create the file
         PrintWriter output = new PrintWriter(number);
         ) {
            for (int i = 0; i <= 100; i++) {
               output.print(((int)(Math.random() * 999) + 1) + " ");
            }
         }
      }
      try (
      Scanner input = new Scanner(number);
      ) {
         int[] numbers = new int[100];
         for (int i = 0; i < 100; i++) {

             numbers[i] = input.nextInt();           
         }
        if (!sorted.exists()) {
           try (
           PrintWriter output = new PrintWriter(sorted)
           ) {
              Arrays.sort(numbers);
              for (int i = 0; i < 100; i ++) {
                 output.print(numbers[i] + " ");
              }
        }
     }
  }
} }

Answer 2

I would suggest extracting to a method the code that writes to the file. Since it would only need a path and content it can be reused for both files and it will make your life way easier.

It is also very helpful if you include the line number where you get the error since it's not always clear where the exception is thrown.

From what I understood from your question the problem is about generating some numbers, write them to a file and lastly sort them and write them to another file. I wrote some code using the same approach but a bit more restructured. I hope it helps.

public static void main(String[] args) {
    int[] randomData = new Random().ints(100).toArray();//just a short way to generate numbers. Use your own.

    File numbers = writteArray("Numbers.txt", randomData);
    Arrays.sort(randomData);
    File sorted = writteArray("Sorted.txt", randomData);
}

public static File writteArray(String Path, int[] randomNumbers){
    File numbers = new File(Path);
    //if the file does not exist it will be created automatically
    try(PrintWriter fileWritter = new PrintWriter(numbers)) {
        //just an example of how to write them. Use your prefered format
        //also you can use the append function to not lose the previous content
        for (int e : randomNumbers)
            fileWritter.printf(" %d", e);
        fileWritter.println();
    }
    catch (FileNotFoundException e){
        e.printStackTrace(); 
    }
    return numbers;
}

As an edit you can make the writeArray() function return void if you don't need the files after.