1. /*
2.  * To change this license header, choose License Headers in Project Properties.
3.  * To change this template file, choose Tools | Templates
4.  * and open the template in the editor.
5.  */
6. package javaapplication5;
7.  
8. import java.io.*;
9.  
10. /**
11.  * @author Daxo
12.  */
13. public class KopiujDane {
14.  
15.   public void copy(File source, File output, int linesToCopy) throws IOException {
16.     validateLineNumber(source, linesToCopy);
17.     validateFile(source);
18.  
19.     if (!output.exists()) {
20.       System.out.println("Plik nie istnieje. Tworzę nowy.");
21.       output.createNewFile();
22.     }
23.  
24.     //Try with resources - używając tego nie trzeba zadeklarowanych streamów zamykać czyli omijamy 'finaly'
25.     try(BufferedReader in = new BufferedReader(new InputStreamReader(new FileInputStream(source)));
26.         FileOutputStream out = new FileOutputStream(output)) {
27.  
28.       for(int i = 0; i < linesToCopy; i++) {
29.         out.write((in.readLine() + "\n").getBytes());
30.       }
31.  
32.     }
33.   }
34.  
35.   private void validateFile(final File source) {
36.     if(!source.exists()) {
37.       throw new IllegalArgumentException("Plik " + source.getAbsolutePath() + " nie istnieje.");
38.     }
39.   }
40.  
41.   private void validateLineNumber(final File source, final int linesToCopy) throws IOException {
42.     if(linesToCopy > countLinesNumber(source)) {
43.       throw new IllegalArgumentException("Liczba linii do skopiowania jest większa niż " +
44.           "rzeczywista liczba linii w pliku");
45.     }
46.   }
47.  
48.   private int countLinesNumber(File file) throws IOException {
49.     int lines = 0;
50.     try(BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(file)))) {
51.       while (reader.readLine() != null) {
52.         lines++;
53.       }
54.     }
55.     return lines;
56.   }
57. }
58.  
59.