/** 1500 bis 1551 */

Filesort.java

import java.io.*;

class Filesort {
  
  static void show (String showfile){
  System.out.println("==== showing "+showfile+" ==========");
    try{
      BufferedReader brin=new BufferedReader(new FileReader(showfile));
      String s1="";
      while ((s1=brin.readLine())!=null)   System.out.println(s1);
      brin.close();
    } catch (Exception e){System.out.println(e);}
    System.out.println("==== showed  "+showfile+" ==========");
  }

  static void copy (String in, String out){
    try{
      BufferedReader brin=new BufferedReader(new FileReader(in));
      BufferedWriter bout=new BufferedWriter(new FileWriter(out));
      String s1="";
      while ((s1=brin.readLine())!=null)   bout.write(s1+"\n");
      bout.close();
      brin.close();
    } catch (Exception e){}
  }

  static boolean sorty (String in, String out){
    boolean result=false;             // true if swapping occured
    try{
      BufferedReader brin=new BufferedReader(new FileReader(in));
      BufferedWriter bout=new BufferedWriter(new FileWriter(out));
      String s1="";
      String s2="";
      String last="";
      while ((s1=brin.readLine())!=null) {
        if (s2.equals("")) s2=brin.readLine();
        int i1=Integer.parseInt(s1.split(";")[0].trim());
        int i2=Integer.parseInt(s2.split(";")[0].trim());
        if (i1<=i2) {
          bout.write(s1+"\n");
          last=s2;
        } else {
          bout.write(s2+"\n");
          s2=s1;
          last=s1;
          result=true;
//          System.out.println("aerks ich musste was tauschen wegen "+i1+" und "+i2);
        }
      }
      bout.write(last+"\n");
      bout.close();
      brin.close();
    } catch (Exception e){}
    return result;
  }

  public static void main (String[]args) {
    Q.p ("Filesort by worgtsone");
    copy ("file01.txt", "file02.txt");
    int coun=0;
    while ( sorty ("file02.txt", "file03.txt") && coun++<999) {
      copy  ("file03.txt", "file02.txt");
      System.out.println(coun);
    }
    show  ("file02.txt");
}}

file01.txt

file02.txt